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// 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;
}