// 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 'framework.dart'; import 'navigator.dart'; import 'routes.dart'; /// Registers a callback to veto attempts by the user to dismiss the enclosing /// [ModalRoute]. /// /// {@tool dartpad} /// Whenever the back button is pressed, you will get a callback at [onWillPop], /// which returns a [Future]. If the [Future] returns true, the screen is /// popped. /// /// ** See code in examples/api/lib/widgets/will_pop_scope/will_pop_scope.0.dart ** /// {@end-tool} /// /// See also: /// /// * [ModalRoute.addScopedWillPopCallback] and [ModalRoute.removeScopedWillPopCallback], /// which this widget uses to register and unregister [onWillPop]. /// * [Form], which provides an `onWillPop` callback that enables the form /// to veto a `pop` initiated by the app's back button. /// class WillPopScope extends StatefulWidget { /// Creates a widget that registers a callback to veto attempts by the user to /// dismiss the enclosing [ModalRoute]. /// /// The [child] argument must not be null. const WillPopScope({ super.key, required this.child, required this.onWillPop, }) : assert(child != null); /// The widget below this widget in the tree. /// /// {@macro flutter.widgets.ProxyWidget.child} final Widget child; /// Called to veto attempts by the user to dismiss the enclosing [ModalRoute]. /// /// If the callback returns a Future that resolves to false, the enclosing /// route will not be popped. final WillPopCallback? onWillPop; @override State<WillPopScope> createState() => _WillPopScopeState(); } class _WillPopScopeState extends State<WillPopScope> { ModalRoute<dynamic>? _route; @override void didChangeDependencies() { super.didChangeDependencies(); if (widget.onWillPop != null) { _route?.removeScopedWillPopCallback(widget.onWillPop!); } _route = ModalRoute.of(context); if (widget.onWillPop != null) { _route?.addScopedWillPopCallback(widget.onWillPop!); } } @override void didUpdateWidget(WillPopScope oldWidget) { super.didUpdateWidget(oldWidget); if (widget.onWillPop != oldWidget.onWillPop && _route != null) { if (oldWidget.onWillPop != null) { _route!.removeScopedWillPopCallback(oldWidget.onWillPop!); } if (widget.onWillPop != null) { _route!.addScopedWillPopCallback(widget.onWillPop!); } } } @override void dispose() { if (widget.onWillPop != null) { _route?.removeScopedWillPopCallback(widget.onWillPop!); } super.dispose(); } @override Widget build(BuildContext context) => widget.child; }