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This PR aims to support Android's predictive back gesture when popping the entire Flutter app. Predictive route transitions between routes inside of a Flutter app will come later. <img width="200" src="https://user-images.githubusercontent.com/389558/217918109-945febaa-9086-41cc-a476-1a189c7831d8.gif" /> ### Trying it out If you want to try this feature yourself, here are the necessary steps: 1. Run Android 33 or above. 1. Enable the feature flag for predictive back on the device under "Developer options". 1. Create a Flutter project, or clone [my example project](https://github.com/justinmc/flutter_predictive_back_examples). 1. Set `android:enableOnBackInvokedCallback="true"` in android/app/src/main/AndroidManifest.xml (already done in the example project). 1. Check out this branch. 1. Run the app. Perform a back gesture (swipe from the left side of the screen). You should see the predictive back animation like in the animation above and be able to commit or cancel it. ### go_router support go_router works with predictive back out of the box because it uses a Navigator internally that dispatches NavigationNotifications! ~~go_router can be supported by adding a listener to the router and updating SystemNavigator.setFrameworkHandlesBack.~~ Similar to with nested Navigators, nested go_routers is supported by using a PopScope widget. <details> <summary>Full example of nested go_routers</summary> ```dart // Copyright 2014 The Flutter Authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. import 'package:go_router/go_router.dart'; import 'package:flutter/material.dart'; import 'package:flutter/scheduler.dart'; void main() => runApp(_MyApp()); class _MyApp extends StatelessWidget { final GoRouter router = GoRouter( routes: <RouteBase>[ GoRoute( path: '/', builder: (BuildContext context, GoRouterState state) => _HomePage(), ), GoRoute( path: '/nested_navigators', builder: (BuildContext context, GoRouterState state) => _NestedGoRoutersPage(), ), ], ); @override Widget build(BuildContext context) { return MaterialApp.router( routerConfig: router, ); } } class _HomePage extends StatelessWidget { @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: const Text('Nested Navigators Example'), ), body: Center( child: Column( mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[ const Text('Home Page'), const Text('A system back gesture here will exit the app.'), const SizedBox(height: 20.0), ListTile( title: const Text('Nested go_router route'), subtitle: const Text('This route has another go_router in addition to the one used with MaterialApp above.'), onTap: () { context.push('/nested_navigators'); }, ), ], ), ), ); } } class _NestedGoRoutersPage extends StatefulWidget { @override State<_NestedGoRoutersPage> createState() => _NestedGoRoutersPageState(); } class _NestedGoRoutersPageState extends State<_NestedGoRoutersPage> { late final GoRouter _router; final GlobalKey<NavigatorState> _nestedNavigatorKey = GlobalKey<NavigatorState>(); // If the nested navigator has routes that can be popped, then we want to // block the root navigator from handling the pop so that the nested navigator // can handle it instead. bool get _popEnabled { // canPop will throw an error if called before build. Is this the best way // to avoid that? return _nestedNavigatorKey.currentState == null ? true : !_router.canPop(); } void _onRouterChanged() { // Here the _router reports the location correctly, but canPop is still out // of date. Hence the post frame callback. SchedulerBinding.instance.addPostFrameCallback((Duration duration) { setState(() {}); }); } @override void initState() { super.initState(); final BuildContext rootContext = context; _router = GoRouter( navigatorKey: _nestedNavigatorKey, routes: [ GoRoute( path: '/', builder: (BuildContext context, GoRouterState state) => _LinksPage( title: 'Nested once - home route', backgroundColor: Colors.indigo, onBack: () { rootContext.pop(); }, buttons: <Widget>[ TextButton( onPressed: () { context.push('/two'); }, child: const Text('Go to another route in this nested Navigator'), ), ], ), ), GoRoute( path: '/two', builder: (BuildContext context, GoRouterState state) => _LinksPage( backgroundColor: Colors.indigo.withBlue(255), title: 'Nested once - page two', ), ), ], ); _router.addListener(_onRouterChanged); } @override void dispose() { _router.removeListener(_onRouterChanged); super.dispose(); } @override Widget build(BuildContext context) { return PopScope( popEnabled: _popEnabled, onPopped: (bool success) { if (success) { return; } _router.pop(); }, child: Router<Object>.withConfig( restorationScopeId: 'router-2', config: _router, ), ); } } class _LinksPage extends StatelessWidget { const _LinksPage ({ required this.backgroundColor, this.buttons = const <Widget>[], this.onBack, required this.title, }); final Color backgroundColor; final List<Widget> buttons; final VoidCallback? onBack; final String title; @override Widget build(BuildContext context) { return Scaffold( backgroundColor: backgroundColor, body: Center( child: Column( mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[ Text(title), //const Text('A system back here will go back to Nested Navigators Page One'), ...buttons, TextButton( onPressed: onBack ?? () { context.pop(); }, child: const Text('Go back'), ), ], ), ), ); } } ``` </details> ### Resources Fixes https://github.com/flutter/flutter/issues/109513 Depends on engine PR https://github.com/flutter/engine/pull/39208 ✔️ Design doc: https://docs.google.com/document/d/1BGCWy1_LRrXEB6qeqTAKlk-U2CZlKJ5xI97g45U7azk/edit# Migration guide: https://github.com/flutter/website/pull/8952 |
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| hello_world | ||
| image_list | ||
| layers | ||
| platform_channel | ||
| platform_channel_swift | ||
| platform_view | ||
| splash | ||
| texture | ||
| .clang-format | ||
| flutter_gallery.readme | ||
| README.md | ||
Flutter Examples
This directory contains several examples of using Flutter. To run an example,
use flutter run inside that example's directory. See the getting started
guide to install the flutter tool.
For additional samples, see the
flutter/samples repo.
Available examples include:
-
Hello, world The hello world app is a minimal Flutter app that shows the text "Hello, world!"
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Flutter gallery The flutter gallery app no longer lives in this repo. Please see the gallery repo.
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Layers The layers vignettes show how to use the various layers in the Flutter framework. For details, see the layers README.
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Platform Channel The platform channel app demonstrates how to connect a Flutter app to platform-specific APIs. For documentation, see https://flutter.dev/platform-channels/.
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Platform Channel Swift The platform channel swift app is the same as platform channel but the iOS version is in Swift and there is no Android version.
Notes
Note on Gradle wrapper files in .gitignore:
Gradle wrapper files should normally be checked into source control. The example projects don't do that to avoid having several copies of the wrapper binary in the Flutter repo. Instead, the Gradle wrapper is injected by Flutter tooling, and the wrapper files are .gitignore'd to avoid making the Flutter repository dirty as a side effect of running the examples.