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<!doctype html><html lang="en"><head><meta charset="utf-8"><title>Optimistic State | Flutter</title><link rel="icon" href="/assets/images/branding/flutter/icon/64.png" eleventy:ignore><link rel="apple-touch-icon" href="/assets/images/branding/flutter/logo/flutter-logomark-320px.png" eleventy:ignore><meta name="viewport" content="width=device-width,initial-scale=1"><meta name="theme-color" content="#ffffff"><link rel="preconnect" href="https://fonts.googleapis.com"><link rel="preconnect" href="https://fonts.gstatic.com" crossorigin><meta name="google-site-verification" content="HFqxhSbf9YA_0rBglNLzDiWnrHiK_w4cqDh2YD2GEY4"><script>!function(e,t,a,n){e[n]=e[n]||[],e[n].push({"gtm.start":(new Date).getTime(),event:"gtm.js"});var 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class="nav-item"><a class="nav-link" href="https://developers.google.com/maps/flutter-package" target="_blank" rel="noopener">Google Maps package</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-5-6" href="#header-sidenav-5-6" role="button" aria-expanded="false" aria-controls="header-sidenav-5-6">News</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-5-6"><li class="nav-item"><a class="nav-link" href="/resources/news-toolkit">Build a news app</a></li></ul></li></ul></li><li aria-hidden="true"><div class="sidebar-primary-divider"></div></li><li class="nav-header">User interface</li><li class="nav-item"><a class="nav-link" href="/ui">Introduction</a></li><li class="nav-item"><a class="nav-link" href="/ui/widgets">Widget catalog</a></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#header-sidenav-10" role="button" aria-expanded="false" aria-controls="header-sidenav-10">Layout</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-10"><li class="nav-item"><a class="nav-link" href="/ui/layout">Introduction</a></li><li class="nav-item"><a class="nav-link" href="/ui/layout/tutorial">Build a layout</a></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-10-3" href="/ui/layout/lists" role="button" aria-expanded="false" aria-controls="header-sidenav-10-3">Lists & grids</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-10-3"><li class="nav-item"><a class="nav-link" href="/cookbook/lists/basic-list">Create and use lists</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/lists/horizontal-list">Create a horizontal list</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/lists/grid-lists">Create a grid view</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/lists/mixed-list">Create lists with different types of items</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/lists/spaced-items">Create lists with spaced items</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/lists/long-lists">Work with long lists</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-10-4" href="/ui/layout/scrolling" role="button" aria-expanded="false" aria-controls="header-sidenav-10-4">Scrolling</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-10-4"><li class="nav-item"><a class="nav-link" href="/ui/layout/scrolling">Overview</a></li><li class="nav-item"><a class="nav-link" href="/ui/layout/scrolling/slivers">Use slivers to achieve fancy scrolling</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/lists/floating-app-bar">Place a floating app bar above a list</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/effects/parallax-scrolling">Create a scrolling parallax effect</a></li></ul></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#header-sidenav-11" role="button" aria-expanded="false" aria-controls="header-sidenav-11">Adaptive & responsive design</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-11"><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive">Overview</a></li><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive/general">General approach</a></li><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive/safearea-mediaquery">SafeArea & MediaQuery</a></li><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive/large-screens">Large screens & foldables</a></li><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive/input">User input & accessibility</a></li><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive/capabilities">Capabilities & policies</a></li><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive/best-practices">Best practices</a></li><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive/more-info">Additional resources</a></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#header-sidenav-12" role="button" aria-expanded="false" aria-controls="header-sidenav-12">Design & theming</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-12"><li class="nav-item"><a class="nav-link" href="/cookbook/design/themes">Share styles with themes</a></li><li class="nav-item"><a class="nav-link" href="/ui/design/material">Material design</a></li><li class="nav-item"><a class="nav-link" href="/release/breaking-changes/material-3-migration">Migrate to Material 3</a></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-12-4" href="/ui/design/text" role="button" aria-expanded="false" aria-controls="header-sidenav-12-4">Text</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-12-4"><li class="nav-item"><a class="nav-link" href="/ui/design/text/typography">Fonts & typography</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/design/fonts">Use a custom font</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/design/package-fonts">Export fonts from a package</a></li><li class="nav-item"><a class="nav-link" href="https://pub.dev/packages/google_fonts" target="_blank" rel="noopener">Google Fonts package</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-12-5" href="/ui/design/graphics" role="button" aria-expanded="false" aria-controls="header-sidenav-12-5">Custom graphics</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-12-5"><li class="nav-item"><a class="nav-link" href="/ui/design/graphics/fragment-shaders">Use custom fragment shaders</a></li></ul></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#header-sidenav-13" role="button" aria-expanded="false" aria-controls="header-sidenav-13">Interactivity</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-13"><li class="nav-item"><a class="nav-link" href="/ui/interactivity">Add interactivity to your app</a></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-13-2" href="/ui/interactivity/gestures" role="button" aria-expanded="false" aria-controls="header-sidenav-13-2">Gestures</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-13-2"><li class="nav-item"><a class="nav-link" href="/ui/interactivity/gestures">Introduction</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/gestures/handling-taps">Handle taps</a></li><li class="nav-item"><a class="nav-link" href="/ui/interactivity/gestures/drag-outside">Drag an object outside an app</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/effects/drag-a-widget">Drag a UI element within an app</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/gestures/ripples">Add Material touch ripples</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/gestures/dismissible">Implement swipe to dismiss</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-13-3" href="/ui/interactivity/input" role="button" aria-expanded="false" aria-controls="header-sidenav-13-3">Input & forms</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-13-3"><li class="nav-item"><a class="nav-link" href="/cookbook/forms/text-input">Create and style a text field</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/forms/retrieve-input">Retrieve the value of a text field</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/forms/text-field-changes">Handle changes to a text field</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/forms/focus">Manage focus in text fields</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/forms/validation">Build a form with validation</a></li></ul></li><li class="nav-item"><a class="nav-link" href="/cookbook/design/snackbars">Display a snackbar</a></li><li class="nav-item"><a class="nav-link" href="/ui/interactivity/actions-and-shortcuts">Implement actions & shortcuts</a></li><li class="nav-item"><a class="nav-link" href="/ui/interactivity/focus">Manage keyboard focus</a></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#header-sidenav-14" role="button" aria-expanded="false" aria-controls="header-sidenav-14">Assets & media</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-14"><li class="nav-item"><a class="nav-link" href="/ui/assets/assets-and-images">Add assets and images</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/images/network-image">Display images from the internet</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/images/fading-in-images">Fade in images with a placeholder</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/plugins/play-video">Play and pause a video</a></li><li class="nav-item"><a class="nav-link" href="/ui/assets/asset-transformation">Transform assets at build time</a></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#header-sidenav-15" role="button" aria-expanded="false" aria-controls="header-sidenav-15">Navigation & routing</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-15"><li class="nav-item"><a class="nav-link" href="/ui/navigation">Overview</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/design/tabs">Add tabs to your app</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/navigation/navigation-basics">Navigate to a new screen and back</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/navigation/passing-data">Send data to a new screen</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/navigation/returning-data">Return data from a screen</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/design/drawer">Add a drawer to a screen</a></li><li class="nav-item"><a class="nav-link" href="/ui/navigation/deep-linking">Set up deep linking</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/navigation/set-up-app-links">Set up app links for Android</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/navigation/set-up-universal-links">Set up universal links for iOS</a></li><li class="nav-item"><a class="nav-link" href="/ui/navigation/url-strategies">Configure web URL strategies</a></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#header-sidenav-16" role="button" aria-expanded="false" aria-controls="header-sidenav-16">Animations & transitions</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-16"><li class="nav-item"><a class="nav-link" href="/ui/animations">Introduction</a></li><li class="nav-item"><a class="nav-link" href="/ui/animations/tutorial">Tutorial</a></li><li class="nav-item"><a class="nav-link" href="/ui/animations/implicit-animations">Implicit animations</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/animation/animated-container">Animate the properties of a container</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/animation/opacity-animation">Fade a widget in and out</a></li><li class="nav-item"><a class="nav-link" href="/ui/animations/hero-animations">Hero animations</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/animation/page-route-animation">Animate a page route transition</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/animation/physics-simulation">Animate using a physics simulation</a></li><li class="nav-item"><a class="nav-link" href="/ui/animations/staggered-animations">Staggered animations</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/effects/staggered-menu-animation">Create a staggered menu animation</a></li><li class="nav-item"><a class="nav-link" href="/ui/animations/overview">API overview</a></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#header-sidenav-17" role="button" aria-expanded="false" aria-controls="header-sidenav-17">Accessibility & internationalization</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-17"><li class="nav-item"><a class="nav-link" href="/ui/accessibility-and-internationalization/accessibility">Accessibility</a></li><li class="nav-item"><a class="nav-link" href="/ui/accessibility-and-internationalization/internationalization">Internationalization</a></li></ul></li><li aria-hidden="true"><div class="sidebar-primary-divider"></div></li><li class="nav-header">Beyond UI</li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#header-sidenav-20" role="button" aria-expanded="false" aria-controls="header-sidenav-20">Data & backend</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-20"><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-20-1" href="/data-and-backend/state-mgmt" role="button" aria-expanded="false" aria-controls="header-sidenav-20-1">State management</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-20-1"><li class="nav-item"><a class="nav-link" href="/data-and-backend/state-mgmt/intro">Introduction</a></li><li class="nav-item"><a class="nav-link" href="/data-and-backend/state-mgmt/declarative">Think declaratively</a></li><li class="nav-item"><a class="nav-link" href="/data-and-backend/state-mgmt/ephemeral-vs-app">Ephemeral vs app state</a></li><li class="nav-item"><a class="nav-link" href="/data-and-backend/state-mgmt/simple">Simple app state management</a></li><li class="nav-item"><a class="nav-link" href="/data-and-backend/state-mgmt/options">Options</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-20-2" href="/data-and-backend/networking" role="button" aria-expanded="false" aria-controls="header-sidenav-20-2">Networking & http</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-20-2"><li class="nav-item"><a class="nav-link" href="/data-and-backend/networking">Overview</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/networking/fetch-data">Fetch data from the internet</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/networking/authenticated-requests">Make authenticated requests</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/networking/send-data">Send data to the internet</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/networking/update-data">Update data over the internet</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/networking/delete-data">Delete data on the internet</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/networking/web-sockets">Communicate with WebSockets</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-20-3" href="/data-and-backend/serialization" role="button" aria-expanded="false" aria-controls="header-sidenav-20-3">Serialization</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-20-3"><li class="nav-item"><a class="nav-link" href="/data-and-backend/serialization/json">JSON serialization</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/networking/background-parsing">Parse JSON in the background</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-20-4" href="/data-and-backend/persistence" role="button" aria-expanded="false" aria-controls="header-sidenav-20-4">Persistence</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-20-4"><li class="nav-item"><a class="nav-link" href="/cookbook/persistence/key-value">Store key-value data on disk</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/persistence/reading-writing-files">Read and write files</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/persistence/sqlite">Persist data with SQLite</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-20-5" href="/data-and-backend/firebase" role="button" aria-expanded="false" aria-controls="header-sidenav-20-5">Firebase</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-20-5"><li class="nav-item"><a class="nav-link" href="/data-and-backend/firebase">Overview</a></li><li class="nav-item"><a class="nav-link" href="https://firebase.google.com/docs/flutter/setup" target="_blank" rel="noopener">Add Firebase to your Flutter app</a></li></ul></li><li class="nav-item"><a class="nav-link" href="/data-and-backend/google-apis">Google APIs</a></li></ul></li><li class="nav-item"><a class="nav-link active collapsible" data-toggle="collapse" href="#header-sidenav-21" role="button" aria-expanded="true" aria-controls="header-sidenav-21">App architecture</a><ul class="nav flex-column flex-nowrap collapse show" id="header-sidenav-21"><li class="nav-item"><a class="nav-link" href="/app-architecture">Introduction</a></li><li class="nav-item"><a class="nav-link" href="/app-architecture/concepts">Architecture concepts</a></li><li class="nav-item"><a class="nav-link" href="/app-architecture/guide">Guide to app architecture</a></li><li class="nav-item"><a class="nav-link" href="/app-architecture/recommendations">Recommendations</a></li><li class="nav-item"><a class="nav-link active collapsible" data-toggle="collapse" data-target="#header-sidenav-21-5" href="/cookbook/architecture" role="button" aria-expanded="true" aria-controls="header-sidenav-21-5">Design patterns</a><ul class="nav flex-column flex-nowrap collapse show" id="header-sidenav-21-5"><li class="nav-item"><a class="nav-link active" href="/cookbook/architecture/optimistic-state">Optimistic state</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/architecture/key-value-data">Persistent storage architecture: Key-value data</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/architecture/sql">Persistent storage architecture: SQL</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/architecture/offline-first">Offline-first</a></li></ul></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#header-sidenav-22" role="button" aria-expanded="false" aria-controls="header-sidenav-22">Platform integration</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-22"><li class="nav-item"><a class="nav-link" href="/reference/supported-platforms">Supported platforms</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/desktop">Build desktop apps with Flutter</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/platform-channels">Write platform-specific code</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/platform-adaptations">Automatic platform adaptations</a></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-22-5" href="/platform-integration/android" role="button" aria-expanded="false" aria-controls="header-sidenav-22-5">Android</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-22-5"><li class="nav-item"><a class="nav-link" href="/platform-integration/android/install-android">Add Android as build target</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/android/splash-screen">Add a splash screen</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/android/predictive-back">Add predictive back</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/android/c-interop">Bind to native code</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/android/platform-views">Host a native Android view</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/android/compose-activity">Launch a Jetpack Compose activity</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/android/restore-state-android">Restore state on Android</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/android/chromeos">Target ChromeOS with Android</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-22-6" href="/platform-integration/ios" role="button" aria-expanded="false" aria-controls="header-sidenav-22-6">iOS</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-22-6"><li class="nav-item"><a class="nav-link" href="/platform-integration/ios/install-ios">Add iOS as build target</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/ios/ios-latest">Flutter on latest iOS</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/ios/apple-frameworks">Leverage Apple's system libraries</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/ios/launch-screen">Add a launch screen</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/ios/ios-app-clip">Add iOS App Clip support</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/ios/app-extensions">Add iOS app extensions</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/ios/c-interop">Bind to native code</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/ios/platform-views">Host a native iOS view</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/ios/ios-debugging">Enable debugging on iOS</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/ios/restore-state-ios">Restore state on iOS</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-22-7" href="/platform-integration/linux" role="button" aria-expanded="false" aria-controls="header-sidenav-22-7">Linux</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-22-7"><li class="nav-item"><a class="nav-link" href="/platform-integration/linux/install-linux">Add Linux as build target</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/linux/building">Build a Linux app</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-22-8" href="/platform-integration/macos" role="button" aria-expanded="false" aria-controls="header-sidenav-22-8">macOS</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-22-8"><li class="nav-item"><a class="nav-link" href="/platform-integration/macos/install-macos">Add macOS as build target</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/macos/building">Build a macOS app</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/macos/c-interop">Bind to native code</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/macos/platform-views">Host a native macOS view</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-22-9" href="/platform-integration/web" role="button" aria-expanded="false" aria-controls="header-sidenav-22-9">Web</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-22-9"><li class="nav-item"><a class="nav-link" href="/platform-integration/web/">Web support in Flutter</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/web/install-web">Add web as build target</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/web/building">Build a web app</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/web/wasm">Compile to WebAssembly</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/web/initialization">Customize app initialization</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/web/embedding-flutter-web">Add Flutter to any web app</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/web/web-content-in-flutter">Web content in Flutter</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/web/renderers">Web renderers</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/web/web-images">Display images on the web</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/web/faq">Web FAQ</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-22-10" href="/platform-integration/windows" role="button" aria-expanded="false" aria-controls="header-sidenav-22-10">Windows</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-22-10"><li class="nav-item"><a class="nav-link" href="/platform-integration/windows/install-windows">Add Windows as build target</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/windows/building">Build a Windows app</a></li></ul></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#header-sidenav-23" role="button" aria-expanded="false" aria-controls="header-sidenav-23">Packages & plugins</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-23"><li class="nav-item"><a class="nav-link" href="/packages-and-plugins/using-packages">Use packages & plugins</a></li><li class="nav-item"><a class="nav-link" href="/packages-and-plugins/developing-packages">Develop packages & plugins</a></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-23-3" href="/packages-and-plugins/swift-package-manager" role="button" aria-expanded="false" aria-controls="header-sidenav-23-3">Swift Package Manager</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-23-3"><li class="nav-item"><a class="nav-link" href="/packages-and-plugins/swift-package-manager/for-app-developers">For app developers</a></li><li class="nav-item"><a class="nav-link" href="/packages-and-plugins/swift-package-manager/for-plugin-authors">For plugin authors</a></li></ul></li><div class="dropdown-divider"></div><li class="nav-item"><a class="nav-link" href="/packages-and-plugins/favorites">Flutter Favorites</a></li><li class="nav-item"><a class="nav-link" href="https://pub.dev/flutter" target="_blank" rel="noopener">Package repository</a></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#header-sidenav-24" role="button" aria-expanded="false" aria-controls="header-sidenav-24">Testing & debugging</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-24"><li class="nav-header">Testing</li><li class="nav-item"><a class="nav-link" href="/testing/overview">Overview</a></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-24-3" href="#header-sidenav-24-3" role="button" aria-expanded="false" aria-controls="header-sidenav-24-3">Unit testing</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-24-3"><li class="nav-item"><a class="nav-link" href="/cookbook/testing/unit/introduction">Introduction</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/testing/unit/mocking">Mock dependencies</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-24-4" href="#header-sidenav-24-4" role="button" aria-expanded="false" aria-controls="header-sidenav-24-4">Widget testing</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-24-4"><li class="nav-item"><a class="nav-link" href="/cookbook/testing/widget/introduction">Introduction</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/testing/widget/finders">Find widgets</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/testing/widget/scrolling">Simulate scrolling</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/testing/widget/tap-drag">Simulate user interaction</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#header-sidenav-24-5" href="#header-sidenav-24-5" role="button" aria-expanded="false" aria-controls="header-sidenav-24-5">Integration testing</a><ul class="nav flex-column flex-nowrap collapse" id="header-sidenav-24-5"><li class="nav-item"><a class="nav-link" href="/cookbook/testing/integration/introduction">Introduction</a></li><li class="nav-item"><a class="nav-link" href="/testing/integration-tests">Write and run an integration test</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/testing/integration/profiling">Profile an integration test</a></li></ul></li><li class="nav-item"><a class="nav-link" href="/testing/testing-plugins">Test a plugin</a></li><li class="nav-item"><a class="nav-link" href="/testing/plugins-in-tests">Handle plugin code in tests</a></li><li class="nav-header">Debugging</li><li class="nav-item"><a class="nav-link" href="/testing/debugging">Debugging tools</a></li><li class="nav-item"><a class="nav-link" href="/testing/code-debugging">Debug your app programmatically</a></li><li class="nav-item"><a class="nav-link" href="/testing/native-debugging">Use a native language debugger</a></li><li class="nav-item"><a class="nav-link" href="/testing/build-modes">Flutter's build modes</a></li><li 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collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-5-3" href="#fixed-sidenav-5-3" role="button" aria-expanded="false" aria-controls="fixed-sidenav-5-3">Games</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-5-3"><li class="nav-item"><a class="nav-link" href="/resources/games-toolkit">Overview</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/games/achievements-leaderboard">Add achievements and leaderboards</a></li><li class="nav-item"><a class="nav-link" href="https://firebase.google.com/codelabs/build-leaderboards-with-firestore#0" target="_blank" rel="noopener">Build leaderboards with Firestore</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/plugins/google-mobile-ads">Add advertising</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/games/firestore-multiplayer">Add multiplayer support</a></li><li class="nav-item"><a class="nav-link" href="https://codelabs.developers.google.com/codelabs/flutter-in-app-purchases" target="_blank" rel="noopener">Add in-app purchases</a></li><li class="nav-item"><a class="nav-link" href="https://firebase.google.com/codelabs/firebase-auth-in-flutter-apps" target="_blank" rel="noopener">Add user authentication</a></li><li class="nav-item"><a class="nav-link" href="https://firebase.google.com/docs/crashlytics/get-started?platform=flutter" target="_blank" rel="noopener">Debug using Crashlytics</a></li><li class="nav-item"><a class="nav-link" href="https://codelabs.developers.google.com/codelabs/flutter-flame-brick-breaker" target="_blank" rel="noopener">Intro to Flame with Flutter</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-5-4" href="#fixed-sidenav-5-4" role="button" aria-expanded="false" aria-controls="fixed-sidenav-5-4">Monetization</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-5-4"><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-5-4-1" href="#fixed-sidenav-5-4-1" role="button" aria-expanded="false" aria-controls="fixed-sidenav-5-4-1">Advertising</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-5-4-1"><li class="nav-item"><a class="nav-link" href="/resources/ads-overview">Ads overview</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/plugins/google-mobile-ads">Add advertising</a></li><li class="nav-item"><a class="nav-link" href="https://codelabs.developers.google.com/codelabs/admob-ads-in-flutter" target="_blank" rel="noopener">Add AdMob ads to your Flutter app</a></li><li class="nav-item"><a class="nav-link" href="https://codelabs.developers.google.com/codelabs/admob-inline-ads-in-flutter" target="_blank" rel="noopener">Add an AdMob banner and native inline ads</a></li><li class="nav-item"><a class="nav-link" href="https://developers.google.com/admob/flutter/mediation" target="_blank" rel="noopener">Google AdMob mediation</a></li><li class="nav-item"><a class="nav-link" href="https://pub.dev/packages/interactive_media_ads" target="_blank" rel="noopener">Interactive Media Ads SDK</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-5-4-2" href="#fixed-sidenav-5-4-2" role="button" aria-expanded="false" aria-controls="fixed-sidenav-5-4-2">In-app purchases</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-5-4-2"><li class="nav-item"><a class="nav-link" href="/resources/in-app-purchases-overview">In-app purchases overview</a></li><li class="nav-item"><a class="nav-link" href="https://codelabs.developers.google.com/codelabs/flutter-in-app-purchases" target="_blank" rel="noopener">Add in-app purchases</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-5-4-3" href="#fixed-sidenav-5-4-3" role="button" aria-expanded="false" aria-controls="fixed-sidenav-5-4-3">Payments</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-5-4-3"><li class="nav-item"><a class="nav-link" href="/resources/payments-overview">Payments overview</a></li><li class="nav-item"><a class="nav-link" href="https://pub.dev/packages/pay" target="_blank" rel="noopener">Google pay package</a></li></ul></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-5-5" href="#fixed-sidenav-5-5" role="button" aria-expanded="false" aria-controls="fixed-sidenav-5-5">Maps</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-5-5"><li class="nav-item"><a class="nav-link" href="https://codelabs.developers.google.com/codelabs/google-maps-in-flutter" target="_blank" rel="noopener">Add Google maps to a Flutter app</a></li><li class="nav-item"><a class="nav-link" href="https://developers.google.com/maps/flutter-package" target="_blank" rel="noopener">Google Maps package</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-5-6" href="#fixed-sidenav-5-6" role="button" aria-expanded="false" aria-controls="fixed-sidenav-5-6">News</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-5-6"><li class="nav-item"><a class="nav-link" href="/resources/news-toolkit">Build a news app</a></li></ul></li></ul></li><li aria-hidden="true"><div class="sidebar-primary-divider"></div></li><li class="nav-header">User interface</li><li class="nav-item"><a class="nav-link" href="/ui">Introduction</a></li><li class="nav-item"><a class="nav-link" href="/ui/widgets">Widget catalog</a></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#fixed-sidenav-10" role="button" aria-expanded="false" aria-controls="fixed-sidenav-10">Layout</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-10"><li class="nav-item"><a class="nav-link" href="/ui/layout">Introduction</a></li><li class="nav-item"><a class="nav-link" href="/ui/layout/tutorial">Build a layout</a></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-10-3" href="/ui/layout/lists" role="button" aria-expanded="false" aria-controls="fixed-sidenav-10-3">Lists & grids</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-10-3"><li class="nav-item"><a class="nav-link" href="/cookbook/lists/basic-list">Create and use lists</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/lists/horizontal-list">Create a horizontal list</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/lists/grid-lists">Create a grid view</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/lists/mixed-list">Create lists with different types of items</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/lists/spaced-items">Create lists with spaced items</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/lists/long-lists">Work with long lists</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-10-4" href="/ui/layout/scrolling" role="button" aria-expanded="false" aria-controls="fixed-sidenav-10-4">Scrolling</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-10-4"><li class="nav-item"><a class="nav-link" href="/ui/layout/scrolling">Overview</a></li><li class="nav-item"><a class="nav-link" href="/ui/layout/scrolling/slivers">Use slivers to achieve fancy scrolling</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/lists/floating-app-bar">Place a floating app bar above a list</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/effects/parallax-scrolling">Create a scrolling parallax effect</a></li></ul></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#fixed-sidenav-11" role="button" aria-expanded="false" aria-controls="fixed-sidenav-11">Adaptive & responsive design</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-11"><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive">Overview</a></li><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive/general">General approach</a></li><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive/safearea-mediaquery">SafeArea & MediaQuery</a></li><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive/large-screens">Large screens & foldables</a></li><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive/input">User input & accessibility</a></li><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive/capabilities">Capabilities & policies</a></li><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive/best-practices">Best practices</a></li><li class="nav-item"><a class="nav-link" href="/ui/adaptive-responsive/more-info">Additional resources</a></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#fixed-sidenav-12" role="button" aria-expanded="false" aria-controls="fixed-sidenav-12">Design & theming</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-12"><li class="nav-item"><a class="nav-link" href="/cookbook/design/themes">Share styles with themes</a></li><li class="nav-item"><a class="nav-link" href="/ui/design/material">Material design</a></li><li class="nav-item"><a class="nav-link" href="/release/breaking-changes/material-3-migration">Migrate to Material 3</a></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-12-4" href="/ui/design/text" role="button" aria-expanded="false" aria-controls="fixed-sidenav-12-4">Text</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-12-4"><li class="nav-item"><a class="nav-link" href="/ui/design/text/typography">Fonts & typography</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/design/fonts">Use a custom font</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/design/package-fonts">Export fonts from a package</a></li><li class="nav-item"><a class="nav-link" href="https://pub.dev/packages/google_fonts" target="_blank" rel="noopener">Google Fonts package</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-12-5" href="/ui/design/graphics" role="button" aria-expanded="false" aria-controls="fixed-sidenav-12-5">Custom graphics</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-12-5"><li class="nav-item"><a class="nav-link" href="/ui/design/graphics/fragment-shaders">Use custom fragment shaders</a></li></ul></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#fixed-sidenav-13" role="button" aria-expanded="false" aria-controls="fixed-sidenav-13">Interactivity</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-13"><li class="nav-item"><a class="nav-link" href="/ui/interactivity">Add interactivity to your app</a></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-13-2" href="/ui/interactivity/gestures" role="button" aria-expanded="false" aria-controls="fixed-sidenav-13-2">Gestures</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-13-2"><li class="nav-item"><a class="nav-link" href="/ui/interactivity/gestures">Introduction</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/gestures/handling-taps">Handle taps</a></li><li class="nav-item"><a class="nav-link" href="/ui/interactivity/gestures/drag-outside">Drag an object outside an app</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/effects/drag-a-widget">Drag a UI element within an app</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/gestures/ripples">Add Material touch ripples</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/gestures/dismissible">Implement swipe to dismiss</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-13-3" href="/ui/interactivity/input" role="button" aria-expanded="false" aria-controls="fixed-sidenav-13-3">Input & forms</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-13-3"><li class="nav-item"><a class="nav-link" href="/cookbook/forms/text-input">Create and style a text field</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/forms/retrieve-input">Retrieve the value of a text field</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/forms/text-field-changes">Handle changes to a text field</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/forms/focus">Manage focus in text fields</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/forms/validation">Build a form with validation</a></li></ul></li><li class="nav-item"><a class="nav-link" href="/cookbook/design/snackbars">Display a snackbar</a></li><li class="nav-item"><a class="nav-link" href="/ui/interactivity/actions-and-shortcuts">Implement actions & shortcuts</a></li><li class="nav-item"><a class="nav-link" href="/ui/interactivity/focus">Manage keyboard focus</a></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#fixed-sidenav-14" role="button" aria-expanded="false" aria-controls="fixed-sidenav-14">Assets & media</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-14"><li class="nav-item"><a class="nav-link" href="/ui/assets/assets-and-images">Add assets and images</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/images/network-image">Display images from the internet</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/images/fading-in-images">Fade in images with a placeholder</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/plugins/play-video">Play and pause a video</a></li><li class="nav-item"><a class="nav-link" href="/ui/assets/asset-transformation">Transform assets at build time</a></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#fixed-sidenav-15" role="button" aria-expanded="false" aria-controls="fixed-sidenav-15">Navigation & routing</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-15"><li class="nav-item"><a class="nav-link" href="/ui/navigation">Overview</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/design/tabs">Add tabs to your app</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/navigation/navigation-basics">Navigate to a new screen and back</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/navigation/passing-data">Send data to a new screen</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/navigation/returning-data">Return data from a screen</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/design/drawer">Add a drawer to a screen</a></li><li class="nav-item"><a class="nav-link" href="/ui/navigation/deep-linking">Set up deep linking</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/navigation/set-up-app-links">Set up app links for Android</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/navigation/set-up-universal-links">Set up universal links for iOS</a></li><li class="nav-item"><a class="nav-link" href="/ui/navigation/url-strategies">Configure web URL strategies</a></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#fixed-sidenav-16" role="button" aria-expanded="false" aria-controls="fixed-sidenav-16">Animations & transitions</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-16"><li class="nav-item"><a class="nav-link" href="/ui/animations">Introduction</a></li><li class="nav-item"><a class="nav-link" href="/ui/animations/tutorial">Tutorial</a></li><li class="nav-item"><a class="nav-link" href="/ui/animations/implicit-animations">Implicit animations</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/animation/animated-container">Animate the properties of a container</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/animation/opacity-animation">Fade a widget in and out</a></li><li class="nav-item"><a class="nav-link" href="/ui/animations/hero-animations">Hero animations</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/animation/page-route-animation">Animate a page route transition</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/animation/physics-simulation">Animate using a physics simulation</a></li><li class="nav-item"><a class="nav-link" href="/ui/animations/staggered-animations">Staggered animations</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/effects/staggered-menu-animation">Create a staggered menu animation</a></li><li class="nav-item"><a class="nav-link" href="/ui/animations/overview">API overview</a></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#fixed-sidenav-17" role="button" aria-expanded="false" aria-controls="fixed-sidenav-17">Accessibility & internationalization</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-17"><li class="nav-item"><a class="nav-link" href="/ui/accessibility-and-internationalization/accessibility">Accessibility</a></li><li class="nav-item"><a class="nav-link" href="/ui/accessibility-and-internationalization/internationalization">Internationalization</a></li></ul></li><li aria-hidden="true"><div class="sidebar-primary-divider"></div></li><li class="nav-header">Beyond UI</li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#fixed-sidenav-20" role="button" aria-expanded="false" aria-controls="fixed-sidenav-20">Data & backend</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-20"><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-20-1" href="/data-and-backend/state-mgmt" role="button" aria-expanded="false" aria-controls="fixed-sidenav-20-1">State management</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-20-1"><li class="nav-item"><a class="nav-link" href="/data-and-backend/state-mgmt/intro">Introduction</a></li><li class="nav-item"><a class="nav-link" href="/data-and-backend/state-mgmt/declarative">Think declaratively</a></li><li class="nav-item"><a class="nav-link" href="/data-and-backend/state-mgmt/ephemeral-vs-app">Ephemeral vs app state</a></li><li class="nav-item"><a class="nav-link" href="/data-and-backend/state-mgmt/simple">Simple app state management</a></li><li class="nav-item"><a class="nav-link" href="/data-and-backend/state-mgmt/options">Options</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-20-2" href="/data-and-backend/networking" role="button" aria-expanded="false" aria-controls="fixed-sidenav-20-2">Networking & http</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-20-2"><li class="nav-item"><a class="nav-link" href="/data-and-backend/networking">Overview</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/networking/fetch-data">Fetch data from the internet</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/networking/authenticated-requests">Make authenticated requests</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/networking/send-data">Send data to the internet</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/networking/update-data">Update data over the internet</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/networking/delete-data">Delete data on the internet</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/networking/web-sockets">Communicate with WebSockets</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-20-3" href="/data-and-backend/serialization" role="button" aria-expanded="false" aria-controls="fixed-sidenav-20-3">Serialization</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-20-3"><li class="nav-item"><a class="nav-link" href="/data-and-backend/serialization/json">JSON serialization</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/networking/background-parsing">Parse JSON in the background</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-20-4" href="/data-and-backend/persistence" role="button" aria-expanded="false" aria-controls="fixed-sidenav-20-4">Persistence</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-20-4"><li class="nav-item"><a class="nav-link" href="/cookbook/persistence/key-value">Store key-value data on disk</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/persistence/reading-writing-files">Read and write files</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/persistence/sqlite">Persist data with SQLite</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#fixed-sidenav-20-5" href="/data-and-backend/firebase" role="button" aria-expanded="false" aria-controls="fixed-sidenav-20-5">Firebase</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-20-5"><li class="nav-item"><a class="nav-link" href="/data-and-backend/firebase">Overview</a></li><li class="nav-item"><a class="nav-link" href="https://firebase.google.com/docs/flutter/setup" target="_blank" rel="noopener">Add Firebase to your Flutter app</a></li></ul></li><li class="nav-item"><a class="nav-link" href="/data-and-backend/google-apis">Google APIs</a></li></ul></li><li class="nav-item"><a class="nav-link active collapsible" data-toggle="collapse" href="#fixed-sidenav-21" role="button" aria-expanded="true" aria-controls="fixed-sidenav-21">App architecture</a><ul class="nav flex-column flex-nowrap collapse show" id="fixed-sidenav-21"><li class="nav-item"><a class="nav-link" href="/app-architecture">Introduction</a></li><li class="nav-item"><a class="nav-link" href="/app-architecture/concepts">Architecture concepts</a></li><li class="nav-item"><a class="nav-link" href="/app-architecture/guide">Guide to app architecture</a></li><li class="nav-item"><a class="nav-link" href="/app-architecture/recommendations">Recommendations</a></li><li class="nav-item"><a class="nav-link active collapsible" data-toggle="collapse" data-target="#fixed-sidenav-21-5" href="/cookbook/architecture" role="button" aria-expanded="true" aria-controls="fixed-sidenav-21-5">Design patterns</a><ul class="nav flex-column flex-nowrap collapse show" id="fixed-sidenav-21-5"><li class="nav-item"><a class="nav-link active" href="/cookbook/architecture/optimistic-state">Optimistic state</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/architecture/key-value-data">Persistent storage architecture: Key-value data</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/architecture/sql">Persistent storage architecture: SQL</a></li><li class="nav-item"><a class="nav-link" href="/cookbook/architecture/offline-first">Offline-first</a></li></ul></li></ul></li><li class="nav-item"><a class="nav-link collapsed collapsible" data-toggle="collapse" href="#fixed-sidenav-22" role="button" aria-expanded="false" aria-controls="fixed-sidenav-22">Platform integration</a><ul class="nav flex-column flex-nowrap collapse" id="fixed-sidenav-22"><li class="nav-item"><a class="nav-link" href="/reference/supported-platforms">Supported platforms</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/desktop">Build desktop apps with Flutter</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/platform-channels">Write platform-specific code</a></li><li class="nav-item"><a class="nav-link" href="/platform-integration/platform-adaptations">Automatic platform adaptations</a></li><li class="nav-item"><a class="nav-link collapsible collapsed" data-toggle="collapse" 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col-xl-8 offset-xl-2 col-xxl-8 offset-xxl-2"><div id="site-toc--side" class="site-toc fixed-col col-xl-2 order-3" data-fixed-column><header class="site-toc__title">Contents</header><ul class="section-nav"><li class="toc-entry nav-item toc-h2"><a class="nav-link" href="#example-feature-a-subscribe-button">Example feature: a subscribe button</a></li><li class="toc-entry nav-item toc-h2"><a class="nav-link" href="#feature-architecture">Feature architecture</a><ul class="nav"><li class="toc-entry nav-item toc-h3"><a class="nav-link" href="#implement-the-subscriptionrepository">Implement the SubscriptionRepository</a></li><li class="toc-entry nav-item toc-h3"><a class="nav-link" href="#implement-the-subscribebuttonviewmodel">Implement the SubscribeButtonViewModel</a></li><li class="toc-entry nav-item toc-h3"><a class="nav-link" href="#implement-the-subscribebutton">Implement the SubscribeButton</a></li><li class="toc-entry nav-item toc-h3"><a class="nav-link" href="#handling-errors">Handling errors</a></li></ul></li><li class="toc-entry nav-item toc-h2"><a class="nav-link" href="#advanced-optimistic-state">Advanced Optimistic State</a></li><li class="toc-entry nav-item toc-h2"><a class="nav-link" href="#interactive-example">Interactive example</a></li></ul></div><div class="container"><header class="site-content__title" id="site-content-title"><h1>Optimistic State</h1><nav class="breadcrumbs" aria-label="breadcrumb"><ol class="breadcrumb-list" vocab="https://schema.org/" typeof="BreadcrumbList"><li class="breadcrumb-item" property="itemListElement" typeof="ListItem"><a href="/cookbook" property="item" typeof="WebPage">Cookbook</a><meta property="position" content="0">chevron_right</li><li class="breadcrumb-item" property="itemListElement" typeof="ListItem"><a href="/cookbook/architecture" property="item" typeof="WebPage">Design patterns</a><meta property="position" content="1">chevron_right</li><li class="breadcrumb-item active" property="itemListElement" typeof="ListItem" aria-current="page"><a href="/cookbook/architecture/optimistic-state" property="item" typeof="WebPage">Optimistic State</a><meta property="position" content="2"></li></ol></nav></header><div id="site-toc--inline" class="site-toc"><header class="site-toc__title">Contents</header><ul class="section-nav"><li class="toc-entry toc-h2"><a href="#example-feature-a-subscribe-button">Example feature: a subscribe button</a></li><li class="toc-entry toc-h2"><a href="#feature-architecture">Feature architecture</a><ul><li class="toc-entry toc-h3"><a href="#implement-the-subscriptionrepository">Implement the SubscriptionRepository</a></li><li class="toc-entry toc-h3"><a href="#implement-the-subscribebuttonviewmodel">Implement the SubscribeButtonViewModel</a></li><li class="toc-entry toc-h3"><a href="#implement-the-subscribebutton">Implement the SubscribeButton</a></li><li class="toc-entry toc-h3"><a href="#handling-errors">Handling errors</a></li></ul></li><li class="toc-entry toc-h2"><a href="#advanced-optimistic-state">Advanced Optimistic State</a></li><li class="toc-entry toc-h2"><a href="#interactive-example">Interactive example</a></li></ul></div> <?code-excerpt path-base="cookbook/architecture/optimistic-state"?> When building user experiences, the perception of performance is sometimes just as important as the actual performance of the code. In general, users don’t like waiting for an action to finish to see the result, and anything that takes more than a few milliseconds could be considered “slow” or “unresponsive” from the user’s perspective.Developers can help mitigate this negative perception by presenting a successful UI state before the background task is fully completed. An example of this would be tapping a “Subscribe” button, and seeing it change to “Subscribed” instantly, even if the background call to the subscription API is still running.This technique is known as Optimistic State, Optimistic UI or Optimistic User Experience. In this recipe, you will implement an application feature using Optimistic State and following the <a href="/app-architecture">Flutter architecture guidelines</a>.<div class="header-wrapper"><h2 id="example-feature-a-subscribe-button">Example feature: a subscribe button</h2><a class="heading-link" href="#example-feature-a-subscribe-button" aria-label="Link to 'Example feature: a subscribe button' section">#</a></div>This example implements a subscribe button similar to the one you could find in a video streaming application or a newsletter.<img src="/assets/images/docs/cookbook/architecture/optimistic-state.png" class="site-mobile-screenshot" alt="Application with subscribe button">When the button is tapped, the application then calls an external API, performing a subscription action, for example recording in a database that the user is now in the subscription list. For demo purposes, you will not implement the actual backend code, instead you will replace this call with a fake action that will simulate a network request.In the case that the call is successful, the button text will change from “Subscribe” to “Subscribed”. The button background color will change as well.On the contrary, if the call fails, the button text should revert back to “Subscribe”, and the UI should show an error message to the user, for example using a Snackbar.Following the Optimistic State idea, the button should instantly change to “Subscribed” once it is tapped, and only change back to “Subscribe” if the request failed.<img src="/assets/images/docs/cookbook/architecture/optimistic-state.gif" class="site-mobile-screenshot" alt="Animation of application with subscribe button"><div class="header-wrapper"><h2 id="feature-architecture">Feature architecture</h2><a class="heading-link" href="#feature-architecture" aria-label="Link to 'Feature architecture' section">#</a></div>Start by defining the feature architecture. Following the architecture guidelines, create these Dart classes in a Flutter project:<ul><li>A <code>StatefulWidget</code> named <code>SubscribeButton</code></li><li>A class named <code>SubscribeButtonViewModel</code> extending <code>ChangeNotifier</code></li><li>A class named <code>SubscriptionRepository</code></li></ul> <?code-excerpt "lib/starter.dart (Starter)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body">dart<pre class="shiki dash-light" tabindex="0"><code>class SubscribeButton extends StatefulWidget { const SubscribeButton({ super.key, }); @override State<SubscribeButton> createState() => _SubscribeButtonState(); } class _SubscribeButtonState extends State<SubscribeButton> { @override Widget build(BuildContext context) { return const Placeholder(); } } class SubscribeButtonViewModel extends ChangeNotifier {} class SubscriptionRepository {}</code></pre></div></div>The <code>SubscribeButton</code> widget and the <code>SubscribeButtonViewModel</code> represent the presentation layer of this solution. The widget is going to display a button that will show the text “Subscribe” or “Subscribed” depending on the subscription state. The view model will contain the subscription state. When the button is tapped, the widget will call the view model to perform the action.The <code>SubscriptionRepository</code> will implement a subscribe method that will throw an exception when the action fails. The view model will call this method when performing the subscription action.Next, connect them together by adding the <code>SubscriptionRepository</code> to the <code>SubscribeButtonViewModel</code>: <?code-excerpt "lib/main.dart (ViewModelStart)" replace="/y;$/y;\n}/g"?> <div class="code-block-wrapper language-dart"><div class="code-block-body">dart<pre class="shiki dash-light" tabindex="0"><code>class SubscribeButtonViewModel extends ChangeNotifier { SubscribeButtonViewModel({ required this.subscriptionRepository, }); final SubscriptionRepository subscriptionRepository; }</code></pre></div></div>And add the <code>SubscribeButtonViewModel</code> to the <code>SubscribeButton</code> widget: <?code-excerpt "lib/main.dart (Widget)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body">dart<pre class="shiki dash-light" tabindex="0"><code>class SubscribeButton extends StatefulWidget { const SubscribeButton({ super.key, required this.viewModel, }); /// Subscribe button view model. final SubscribeButtonViewModel viewModel; @override State<SubscribeButton> createState() => _SubscribeButtonState(); }</code></pre></div></div>Now that you have created the basic solution architecture, you can create the <code>SubscribeButton</code> widget the following way: <?code-excerpt "lib/main.dart (SubscribeButton)" replace="/^child: //g;/^\),$/)/g"?> <div class="code-block-wrapper language-dart"><div class="code-block-body">dart<pre class="shiki dash-light" tabindex="0"><code>SubscribeButton( viewModel: SubscribeButtonViewModel( subscriptionRepository: SubscriptionRepository(), ), )</code></pre></div></div><div class="header-wrapper"><h3 id="implement-the-subscriptionrepository">Implement the <code>SubscriptionRepository</code></h3><a class="heading-link" href="#implement-the-subscriptionrepository" aria-label="Link to 'Implement the SubscriptionRepository' section">#</a></div>Add a new asynchronous method named <code>subscribe()</code> to the <code>SubscriptionRepository</code> with the following code: <?code-excerpt "lib/main.dart (SubscriptionRepository)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body">dart<pre class="shiki dash-light" tabindex="0"><code>class SubscriptionRepository { /// Simulates a network request and then fails. Future<void> subscribe() async { // Simulate a network request await Future.delayed(const Duration(seconds: 1)); // Fail after one second throw Exception('Failed to subscribe'); } }</code></pre></div></div>The call to <code>await Future.delayed()</code> with a duration of one second has been added to simulate a long running request. The method execution will pause for a second, and then it will continue running.In order to simulate a request failing, the subscribe method throws an exception at the end. This will be used later on to show how to recover from a failed request when implementing Optimistic State.<div class="header-wrapper"><h3 id="implement-the-subscribebuttonviewmodel">Implement the <code>SubscribeButtonViewModel</code></h3><a class="heading-link" href="#implement-the-subscribebuttonviewmodel" aria-label="Link to 'Implement the SubscribeButtonViewModel' section">#</a></div>To represented the subscription state, as well a possible error state, add the following public members to the <code>SubscribeButtonViewModel</code>: <?code-excerpt "lib/main.dart (States)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body">dart<pre class="shiki dash-light" tabindex="0"><code>// Whether the user is subscribed bool subscribed = false; // Whether the subscription action has failed bool error = false;</code></pre></div></div>Both are set to <code>false</code> on start.Following the ideas of Optimistic State, the <code>subscribed</code> state will change to <code>true</code> as soon as the user taps the subscribe button. And will only change back to <code>false</code> if the action fails.The <code>error</code> state will change to <code>true</code> when the action fails, indicating the <code>SubscribeButton</code> widget to show an error message to the user. The variable should go back to <code>false</code> once the error has been displayed.Next, implement an asynchronous <code>subscribe()</code> method: <?code-excerpt "lib/main.dart (subscribe)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body">dart<pre class="shiki dash-light" tabindex="0"><code>// Subscription action Future<void> subscribe() async { // Ignore taps when subscribed if (subscribed) { return; } // Optimistic state. // It will be reverted if the subscription fails. subscribed = true; // Notify listeners to update the UI notifyListeners(); try { await subscriptionRepository.subscribe(); } catch (e) { print('Failed to subscribe: $e'); // Revert to the previous state subscribed = false; // Set the error state error = true; } finally { notifyListeners(); } }</code></pre></div></div>As described previously, first the method sets the <code>subscribed</code> state to <code>true</code> and then calls to <code>notifyListeners()</code>. This forces the UI to update and the button changes its appearance, showing the text “Subscribed” to the user.Then the method performs the actual call to the repository. This call is wrapped by a <code>try-catch</code> in order to catch any exceptions it may throw. In case an exception is caught, the <code>subscribed</code> state is set back to <code>false</code>, and the <code>error</code> state is set to <code>true</code>. A final call to <code>notifyListeners()</code> is done to change the UI back to ‘Subscribe’.If there is no exception, the process is complete because the UI is already reflecting the success state.The complete <code>SubscribeButtonViewModel</code> should look like this: <?code-excerpt "lib/main.dart (ViewModelFull)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body">dart<pre class="shiki dash-light" tabindex="0"><code>/// Subscribe button View Model. /// Handles the subscribe action and exposes the state to the subscription. class SubscribeButtonViewModel extends ChangeNotifier { SubscribeButtonViewModel({ required this.subscriptionRepository, }); final SubscriptionRepository subscriptionRepository; // Whether the user is subscribed bool subscribed = false; // Whether the subscription action has failed bool error = false; // Subscription action Future<void> subscribe() async { // Ignore taps when subscribed if (subscribed) { return; } // Optimistic state. // It will be reverted if the subscription fails. subscribed = true; // Notify listeners to update the UI notifyListeners(); try { await subscriptionRepository.subscribe(); } catch (e) { print('Failed to subscribe: $e'); // Revert to the previous state subscribed = false; // Set the error state error = true; } finally { notifyListeners(); } } }</code></pre></div></div><div class="header-wrapper"><h3 id="implement-the-subscribebutton">Implement the <code>SubscribeButton</code></h3><a class="heading-link" href="#implement-the-subscribebutton" aria-label="Link to 'Implement the SubscribeButton' section">#</a></div>In this step, you will first implement the build method of the <code>SubscribeButton</code>, and then implement the feature’s error handling.Add the following code to the build method: <?code-excerpt "lib/main.dart (build)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body">dart<pre class="shiki dash-light" tabindex="0"><code>@override Widget build(BuildContext context) { return ListenableBuilder( listenable: widget.viewModel, builder: (context, _) { return FilledButton( onPressed: widget.viewModel.subscribe, style: widget.viewModel.subscribed ? SubscribeButtonStyle.subscribed : SubscribeButtonStyle.unsubscribed, child: widget.viewModel.subscribed ? const Text('Subscribed') : const Text('Subscribe'), ); }, ); }</code></pre></div></div>This build method contains a <code>ListenableBuilder</code> that listens to changes from the view model. The builder then creates a <code>FilledButton</code> that will display the text "Subscribed" or "Subscribe" depending on the view model state. The button style will also change depending on this state. As well, when the button is tapped, it runs the <code>subscribe()</code> method from the view model.The <code>SubscribeButtonStyle</code> can be found here. Add this class next to the <code>SubscribeButton</code>. Feel free to modify the <code>ButtonStyle</code>. <?code-excerpt "lib/main.dart (style)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body">dart<pre class="shiki dash-light" tabindex="0"><code>class SubscribeButtonStyle { static const unsubscribed = ButtonStyle( backgroundColor: WidgetStatePropertyAll(Colors.red), ); static const subscribed = ButtonStyle( backgroundColor: WidgetStatePropertyAll(Colors.green), ); }</code></pre></div></div>If you run the application now, you will see how the button changes when you press it, however it will change back to the original state without showing an error.<div class="header-wrapper"><h3 id="handling-errors">Handling errors</h3><a class="heading-link" href="#handling-errors" aria-label="Link to 'Handling errors' section">#</a></div>To handle errors, add the <code>initState()</code> and <code>dispose()</code> methods to the <code>SubscribeButtonState</code>, and then add the <code>_onViewModelChange()</code> method. <?code-excerpt "lib/main.dart (listener1)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body">dart<pre class="shiki dash-light" tabindex="0"><code>@override void initState() { super.initState(); widget.viewModel.addListener(_onViewModelChange); } @override void dispose() { widget.viewModel.removeListener(_onViewModelChange); super.dispose(); }</code></pre></div></div><?code-excerpt "lib/main.dart (listener2)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body">dart<pre class="shiki dash-light" tabindex="0"><code>/// Listen to ViewModel changes. void _onViewModelChange() { // If the subscription action has failed if (widget.viewModel.error) { // Reset the error state widget.viewModel.error = false; // Show an error message ScaffoldMessenger.of(context).showSnackBar( const SnackBar( content: Text('Failed to subscribe'), ), ); } }</code></pre></div></div>The <code>addListener()</code> call registers the <code>_onViewModelChange()</code> method to be called when the view model notifies listeners. It’s important to call <code>removeListener()</code> when the widget is disposed of, in order to avoid errors.The <code>_onViewModelChange()</code> method checks the <code>error</code> state, and if it is <code>true</code>, displays a <code>Snackbar</code> to the user showing an error message. As well, the <code>error</code> state is set back to <code>false</code>, to avoid displaying the error message multiple times if <code>notifyListeners()</code> is called again in the view model.<div class="header-wrapper"><h2 id="advanced-optimistic-state">Advanced Optimistic State</h2><a class="heading-link" href="#advanced-optimistic-state" aria-label="Link to 'Advanced Optimistic State' section">#</a></div>In this tutorial, you’ve learned how to implement an Optimistic State with a single binary state, but you can use this technique to create a more advanced solution by incorporating a third temporal state that indicates that the action is still running.For example, in a chat application when the user sends a new message, the application will display the new chat message in the chat window, but with an icon indicating that the message is still pending to be delivered. When the message is delivered, that icon would be removed.In the subscribe button example, you could add another flag in the view model indicating that the <code>subscribe()</code> method is still running, or use the Command pattern running state, then modify the button style slightly to show that the operation is running.<div class="header-wrapper"><h2 id="interactive-example">Interactive example</h2><a class="heading-link" href="#interactive-example" aria-label="Link to 'Interactive example' section">#</a></div>This example shows the <code>SubscribeButton</code> widget together with the <code>SubscribeButtonViewModel</code> and <code>SubscriptionRepository</code>, which implement a subscribe tap action with Optimistic State.When you tap the button, the button text changes from “Subscribe” to “Subscribed”. After a second, the repository throws an exception, which gets captured by the view model, and the button reverts back to showing “Subscribe”, while also displaying a Snackbar with an error message. <?code-excerpt "lib/main.dart"?> <pre><code data-dartpad="true" data-embed="true" data-theme="light" title="Flutter Optimistic State example in DartPad" data-run="true">// ignore_for_file: avoid_print import 'package:flutter/material.dart'; void main() { runApp(const MyApp()); } class MyApp extends StatelessWidget { const MyApp({super.key}); // This widget is the root of your application. @override Widget build(BuildContext context) { return MaterialApp( home: Scaffold( body: Center( child: SubscribeButton( viewModel: SubscribeButtonViewModel( subscriptionRepository: SubscriptionRepository(), ), ), ), ), ); } } /// A button that simulates a subscription action. /// For example, subscribing to a newsletter or a streaming channel. class SubscribeButton extends StatefulWidget { const SubscribeButton({ super.key, required this.viewModel, }); /// Subscribe button view model. final SubscribeButtonViewModel viewModel; @override State<SubscribeButton> createState() => _SubscribeButtonState(); } class _SubscribeButtonState extends State<SubscribeButton> { @override void initState() { super.initState(); widget.viewModel.addListener(_onViewModelChange); } @override void dispose() { widget.viewModel.removeListener(_onViewModelChange); super.dispose(); } @override Widget build(BuildContext context) { return ListenableBuilder( listenable: widget.viewModel, builder: (context, _) { return FilledButton( onPressed: widget.viewModel.subscribe, style: widget.viewModel.subscribed ? SubscribeButtonStyle.subscribed : SubscribeButtonStyle.unsubscribed, child: widget.viewModel.subscribed ? const Text('Subscribed') : const Text('Subscribe'), ); }, ); } /// Listen to ViewModel changes. void _onViewModelChange() { // If the subscription action has failed if (widget.viewModel.error) { // Reset the error state widget.viewModel.error = false; // Show an error message ScaffoldMessenger.of(context).showSnackBar( const SnackBar( content: Text('Failed to subscribe'), ), ); } } } class SubscribeButtonStyle { static const unsubscribed = ButtonStyle( backgroundColor: WidgetStatePropertyAll(Colors.red), ); static const subscribed = ButtonStyle( backgroundColor: WidgetStatePropertyAll(Colors.green), ); } /// Subscribe button View Model. /// Handles the subscribe action and exposes the state to the subscription. class SubscribeButtonViewModel extends ChangeNotifier { SubscribeButtonViewModel({ required this.subscriptionRepository, }); final SubscriptionRepository subscriptionRepository; // Whether the user is subscribed bool subscribed = false; // Whether the subscription action has failed bool error = false; // Subscription action Future<void> subscribe() async { // Ignore taps when subscribed if (subscribed) { return; } // Optimistic state. // It will be reverted if the subscription fails. subscribed = true; // Notify listeners to update the UI notifyListeners(); try { await subscriptionRepository.subscribe(); } catch (e) { print('Failed to subscribe: $e'); // Revert to the previous state subscribed = false; // Set the error state error = true; } finally { notifyListeners(); } } } /// Repository of subscriptions. class SubscriptionRepository { /// Simulates a network request and then fails. Future<void> subscribe() async { // Simulate a network request await Future.delayed(const Duration(seconds: 1)); // Fail after one second throw Exception('Failed to subscribe'); } } </code></pre>Unless stated otherwise, the documentation on this site reflects the latest stable version of Flutter. 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