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Migration guide for predictive back #8952

Merged

justinmc merged 7 commits into flutter:main from justinmc:predictive-back

Aug 7, 2023

Contributor

justinmc commented Jun 27, 2023 •

edited

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Migration guide for Android 14's Predictive Back feature, which deprecates and replaces several navigation APIs.

Related PRs:
flutter/flutter#120385
flutter/engine#39208

TODOs

~~Insert the "landed in" version number.~~
Leave a comment on these blog posts
- https://blog.logrocket.com/using-willpopscope-flutter-android-navigation/
- https://www.flutterant.com/working-with-willpopscope-widget/

Presubmit checklist

This PR doesn’t contain automatically generated corrections (Grammarly or similar).
This PR follows the Google Developer Documentation Style Guidelines — for example, it doesn’t use i.e. or e.g., and it avoids I and we (first person).
This PR uses semantic line breaks of 80 characters or fewer.


          Start of a migration guide for predictive back

0aafccc

justinmc self-assigned this

justinmc mentioned this pull request

Predictive back support for root routes flutter/flutter#120385

Merged


          Final sections and technical details in Background section

5f19de4

sfshaza2 approved these changes

View reviewed changes

Contributor

sfshaza2 left a comment

LGTM with some edits. Once it's certain that it's going into the release, it can be merged into the 3.13 branch. I'm also adding the appropriate label.

src/release/breaking-changes/android-predictive-back.md Outdated

+              With predictive back, the back animation begins immediately when the
+              user initiates the gesture and before it has been committed. There is no
+              opportunity for the Flutter app to decide whether or not it is allowed to happen

Contributor

sfshaza2 Jul 31, 2023

Suggested change

      
            opportunity for the Flutter app to decide whether or not it is allowed to happen
          
            opportunity for the Flutter app to decide whether it's allowed to happen

src/release/breaking-changes/android-predictive-back.md Outdated

Comment on lines 53 to 54

		These replace parameters that corresponded with `WillPopScope` and now are used
		with `PopScope` in the same was as above.

Contributor

sfshaza2 Jul 31, 2023

Fields? Properties? Methods? It seems like one is a property and the other is a method?

Suggested change

      
            These replace parameters that corresponded with `WillPopScope` and now are used
          
            with `PopScope` in the same was as above.
          
            These fields replace parameters that corresponded with `WillPopScope`
          
            and are now used with `PopScope` in the same way as above.

src/release/breaking-changes/android-predictive-back.md Outdated

Comment on lines 76 to 78

+              These are used internally to register `PopScope` widgets, so that they are taken
+              into consideration when the route decides whether or not it can pop. This may be
+              used if implementing a custom `PopScope` widget.

Contributor

sfshaza2 Jul 31, 2023

Suggested change

      
            These are used internally to register `PopScope` widgets, so that they are taken
          
            into consideration when the route decides whether or not it can pop. This may be
          
            used if implementing a custom `PopScope` widget.
          
            Use these methods to register `PopScope` widgets,
          
            to be evaluated when the route decides
          
            whether it can pop. This functionality might be
          
            used when implementing a custom `PopScope` widget.

src/release/breaking-changes/android-predictive-back.md Outdated

Comment on lines 38 to 41

+              `PopScope` is a direct replacement for `WillPopScope`. Instead of deciding
+              whether or not a pop is possible at the time it occurs, this is set ahead of
+              time with the `canPop` boolean. It's also still possible to listen to pops by
+              using `onPopInvoked`.

Contributor

sfshaza2 Jul 31, 2023

Suggested change

      
            `PopScope` is a direct replacement for `WillPopScope`. Instead of deciding
          
            whether or not a pop is possible at the time it occurs, this is set ahead of
          
            time with the `canPop` boolean. It's also still possible to listen to pops by
          
            using `onPopInvoked`.
          
            The `PopScope` class directly replaces `WillPopScope`.
          
            Instead of deciding whether a pop is possible at the time it occurs,
          
            this is set ahead of time with the `canPop` boolean.
          
            You can still listen to pops by using `onPopInvoked`.

src/release/breaking-changes/android-predictive-back.md Outdated

Comment on lines 11 to 13

+              Flutter's just-in-time navigation APIs, like `WillPopScope` and
+              `Navigator.willPop`, are being replaced with a set of ahead-of-time APIs in
+              order to support Android 14's Predictive Back feature.

Contributor

sfshaza2 Jul 31, 2023

Suggested change

      
            Flutter's just-in-time navigation APIs, like `WillPopScope` and
          
            `Navigator.willPop`, are being replaced with a set of ahead-of-time APIs in
          
            order to support Android 14's Predictive Back feature.
          
            To support Android 14's Predictive Back feature,
          
            a set of ahead-of-time APIs have replaced just-in-time
          
            navigation APIs, like `WillPopScope` and `Navigator.willPop`.

src/release/breaking-changes/android-predictive-back.md Outdated

+              Android 14 introduced the
+              [Predictive Back feature](https://developer.android.com/guide/navigation/predictive-back-gesture),
+              which allows the user to peek behind the current route during a valid back
+              gesture and decide whether or not to continue back or to cancel the gesture.

Contributor

sfshaza2 Jul 31, 2023

Suggested change

      
            gesture and decide whether or not to continue back or to cancel the gesture.
          
            gesture and decide whether to continue back or to cancel the gesture.

src/release/breaking-changes/android-predictive-back.md Outdated

Comment on lines 177 to 180

+              `Form` used to use a `WillPopScope` under the hood and expose its `onWillPop`
+              method. It has been replaced with a `PopScope` and has exposed its `canPop` and
+              `onPopInvoked` methods. Migrating is identical to migrating from `WillPopScope`
+              to `PopScope`, detailed above.

Contributor

sfshaza2 Jul 31, 2023

Suggested change

      
            `Form` used to use a `WillPopScope` under the hood and expose its `onWillPop`
          
            method. It has been replaced with a `PopScope` and has exposed its `canPop` and
          
            `onPopInvoked` methods. Migrating is identical to migrating from `WillPopScope`
          
            to `PopScope`, detailed above.
          
            Previously, `Form` used a `WillPopScope` instance under the hood
          
            and exposed its `onWillPop` method. This has been replaced with a
          
            `PopScope` that exposes its `canPop` and `onPopInvoked` methods.
          
            Migrating is identical to migrating from `WillPopScope`
          
            to `PopScope`, detailed above.

src/release/breaking-changes/android-predictive-back.md Outdated

Comment on lines 206 to 207

		`removeScopedWillPopCallback`. Since `WillPopScope` has been replaced by
		`PopScope`, these methods have been replaced by `registerPopInterface` and

Contributor

sfshaza2 Jul 31, 2023

Suggested change

      
            `removeScopedWillPopCallback`. Since `WillPopScope` has been replaced by
          
            `PopScope`, these methods have been replaced by `registerPopInterface` and
          
            `removeScopedWillPopCallback`. Since `PopScope` replaces `WillPopScope`,
          
            these methods have been replaced by `registerPopInterface` and

sfshaza2 added the act.merge-to-next label

justinmc added 4 commits

August 1, 2023 15:46


          Version number and fix for PopEntry registration made in PR too

e90c97c


          it's, and reworded a paragraph

ec56e96


          Last review rewording

a8aa178


          Merge remote-tracking branch 'upstream/main' into predictive-back

bc2f56e

Contributor Author

justinmc commented Aug 1, 2023

Thanks! Changes made. I'll plan to merge this after the flutter/flutter PR goes in.

auto-submit bot pushed a commit to flutter/flutter that referenced this pull request


          Predictive back support for root routes (#120385)

dedd100

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 #109513
Depends on engine PR flutter/engine#39208 ✔️ 
Design doc: https://docs.google.com/document/d/1BGCWy1_LRrXEB6qeqTAKlk-U2CZlKJ5xI97g45U7azk/edit#
Migration guide: flutter/website#8952


          Merge remote-tracking branch 'upstream/main' into predictive-back

f16aeb6

justinmc marked this pull request as ready for review

August 4, 2023 22:16

justinmc requested review from atsansone and parlough as code owners

August 4, 2023 22:16

Contributor Author

justinmc commented Aug 4, 2023

The related PRs have merged so this can be merged too now if the checks pass.

justinmc merged commit 80151fc into flutter:main

9 checks passed

justinmc deleted the predictive-back branch

August 7, 2023 22:21

justinmc mentioned this pull request

Predictive back migration guide confirmation dialog example #9244

Merged

parlough added a commit that referenced this pull request


          Predictive back migration guide confirmation dialog example (#9244)

c42ad96

A user requested this example be added to the migration guide [on
Discord](https://discord.com/channels/608014603317936148/969301283825659914/1140422179511603290).
I think it's a reasonable request.

Follow up on: #8952
Framework PR: flutter/flutter#132249

---------

Co-authored-by: Parker Lougheed <parlough@gmail.com>

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