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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 'package:flutter/material.dart';
import 'package:flutter/services.dart';
/// This sample demonstrates showing a confirmation dialog when the user
/// attempts to navigate away from a page with unsaved [Form] data.
void main() => runApp(const FormApp());
class FormApp extends StatelessWidget {
const FormApp({
super.key,
});
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
appBar: AppBar(
title: const Text('Confirmation Dialog Example'),
),
body: Center(
child: _SaveableForm(),
),
),
);
}
}
class _SaveableForm extends StatefulWidget {
@override
State<_SaveableForm> createState() => _SaveableFormState();
}
class _SaveableFormState extends State<_SaveableForm> {
final TextEditingController _controller = TextEditingController();
String _savedValue = '';
bool _isDirty = false;
@override
void initState() {
super.initState();
_controller.addListener(_onChanged);
}
@override
void dispose() {
_controller.removeListener(_onChanged);
super.dispose();
}
void _onChanged() {
final bool nextIsDirty = _savedValue != _controller.text;
if (nextIsDirty == _isDirty) {
return;
}
setState(() {
_isDirty = nextIsDirty;
});
}
Future<void> _showDialog() async {
final bool? shouldDiscard = await showDialog<bool>(
context: context,
builder: (BuildContext context) {
return AlertDialog(
title: const Text('Are you sure?'),
content: const Text('Any unsaved changes will be lost!'),
actions: <Widget>[
TextButton(
child: const Text('Yes, discard my changes'),
onPressed: () {
Navigator.pop(context, true);
},
),
TextButton(
child: const Text('No, continue editing'),
onPressed: () {
Navigator.pop(context, false);
},
),
],
);
},
);
if (shouldDiscard ?? false) {
// Since this is the root route, quit the app where possible by invoking
// the SystemNavigator. If this wasn't the root route, then
// Navigator.maybePop could be used instead.
// See https://github.com/flutter/flutter/issues/11490
SystemNavigator.pop();
}
}
void _save(String? value) {
setState(() {
_savedValue = value ?? '';
});
}
@override
Widget build(BuildContext context) {
return Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
const Text('If the field below is unsaved, a confirmation dialog will be shown on back.'),
const SizedBox(height: 20.0),
Form(
canPop: !_isDirty,
onPopInvoked: (bool didPop) {
if (didPop) {
return;
}
_showDialog();
},
autovalidateMode: AutovalidateMode.always,
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
TextFormField(
controller: _controller,
onFieldSubmitted: (String? value) {
_save(value);
},
),
TextButton(
onPressed: () {
_save(_controller.text);
},
child: Row(
children: <Widget>[
const Text('Save'),
if (_controller.text.isNotEmpty)
Icon(
_isDirty ? Icons.warning : Icons.check,
),
],
),
),
],
),
),
TextButton(
onPressed: () {
if (_isDirty) {
_showDialog();
return;
}
// Since this is the root route, quit the app where possible by
// invoking the SystemNavigator. If this wasn't the root route,
// then Navigator.maybePop could be used instead.
// See https://github.com/flutter/flutter/issues/11490
SystemNavigator.pop();
},
child: const Text('Go back'),
),
],
),
);
}
}