从一个页面回传数据
在某些场景下，我们需要在回退到上一屏时同时返回一些数据。比如，我们跳转到新的一屏，有两个选项让用户选择，当用户点击某个选项后会返回到第一屏，同时在第一屏可以知道用户选择的信息。
你可以使用 Navigator.pop() 来进行以下步骤：
步骤
-
创建主屏界面
-
添加按钮，点击时跳转到选择界面
-
在选择界面显示两个按钮
-
当任意一个按钮被点击，关闭选择界面回退到主屏界面
-
在主屏界面显示 snackbar ，展示选中的项目
1. 创建主屏界面
主屏界面显示一个按钮，当点击按钮时跳转到选择界面。
class HomeScreen extends StatelessWidget {
const HomeScreen({super.key});
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('Returning Data Demo'),
),
// Create the SelectionButton widget in the next step.
body: const Center(
child: SelectionButton(),
),
);
}
}2. 添加按钮，点击时跳转到选择界面
接下来，我们创建 SelectionButton 按钮，它有两个功能：
-
点击时跳转到选择界面
-
等待选择界面给它返回结果
class SelectionButton extends StatefulWidget {
const SelectionButton({super.key});
@override
State<SelectionButton> createState() => _SelectionButtonState();
}
class _SelectionButtonState extends State<SelectionButton> {
@override
Widget build(BuildContext context) {
return ElevatedButton(
onPressed: () {
_navigateAndDisplaySelection(context);
},
child: const Text('Pick an option, any option!'),
);
}
Future<void> _navigateAndDisplaySelection(BuildContext context) async {
// Navigator.push returns a Future that completes after calling
// Navigator.pop on the Selection Screen.
final result = await Navigator.push(
context,
// Create the SelectionScreen in the next step.
MaterialPageRoute(builder: (context) => const SelectionScreen()),
);
}
}3. 在选择界面显示两个按钮
现在来构建选择界面，它包含两个按钮，当任意一个按钮被点击的时候，关闭选择页面回退到主屏界面，并让主屏界面知道哪个按钮被点击了。
这一步我们来定义 UI，在下一步完成数据的返回。
class SelectionScreen extends StatelessWidget {
const SelectionScreen({super.key});
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('Pick an option'),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Padding(
padding: const EdgeInsets.all(8),
child: ElevatedButton(
onPressed: () {
// Pop here with "Yep"...
},
child: const Text('Yep!'),
),
),
Padding(
padding: const EdgeInsets.all(8),
child: ElevatedButton(
onPressed: () {
// Pop here with "Nope"...
},
child: const Text('Nope.'),
),
)
],
),
),
);
}
}4. 当任意一个按钮被点击，关闭选择界面回退到主屏界面
接下来我们来更新两个按钮的 onPressed() 回调函数，使用 Navigator.pop() 回退界面并返回数据给主屏界面。
Navigator.pop() 方法可以接受第二个参数 result，它是可选的，如果传递了 result，数据将会通过 Future 方法的返回值传递。
Yep 按钮
ElevatedButton(
onPressed: () {
// Close the screen and return "Yep!" as the result.
Navigator.pop(context, 'Yep!');
},
child: const Text('Yep!'),
)Nope 按钮
ElevatedButton(
onPressed: () {
// Close the screen and return "Nope." as the result.
Navigator.pop(context, 'Nope.');
},
child: const Text('Nope.'),
)5. 在主屏界面显示一个 snackbar，展示选中的项目
现在，我们跳转到选择界面并等待返回结果，当结果返回时我们可以做些事情。
在本例中，我们用一个 snackbar 显示结果，我们来更新 SelectionButton 类中的 _navigateAndDisplaySelection() 方法。
// A method that launches the SelectionScreen and awaits the result from
// Navigator.pop.
Future<void> _navigateAndDisplaySelection(BuildContext context) async {
// Navigator.push returns a Future that completes after calling
// Navigator.pop on the Selection Screen.
final result = await Navigator.push(
context,
MaterialPageRoute(builder: (context) => const SelectionScreen()),
);
// When a BuildContext is used from a StatefulWidget, the mounted property
// must be checked after an asynchronous gap.
if (!context.mounted) return;
// After the Selection Screen returns a result, hide any previous snackbars
// and show the new result.
ScaffoldMessenger.of(context)
..removeCurrentSnackBar()
..showSnackBar(SnackBar(content: Text('$result')));
}交互式样例
import 'package:flutter/material.dart';
void main() {
runApp(
const MaterialApp(
title: 'Returning Data',
home: HomeScreen(),
),
);
}
class HomeScreen extends StatelessWidget {
const HomeScreen({super.key});
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('Returning Data Demo'),
),
body: const Center(
child: SelectionButton(),
),
);
}
}
class SelectionButton extends StatefulWidget {
const SelectionButton({super.key});
@override
State<SelectionButton> createState() => _SelectionButtonState();
}
class _SelectionButtonState extends State<SelectionButton> {
@override
Widget build(BuildContext context) {
return ElevatedButton(
onPressed: () {
_navigateAndDisplaySelection(context);
},
child: const Text('Pick an option, any option!'),
);
}
// A method that launches the SelectionScreen and awaits the result from
// Navigator.pop.
Future<void> _navigateAndDisplaySelection(BuildContext context) async {
// Navigator.push returns a Future that completes after calling
// Navigator.pop on the Selection Screen.
final result = await Navigator.push(
context,
MaterialPageRoute(builder: (context) => const SelectionScreen()),
);
// When a BuildContext is used from a StatefulWidget, the mounted property
// must be checked after an asynchronous gap.
if (!context.mounted) return;
// After the Selection Screen returns a result, hide any previous snackbars
// and show the new result.
ScaffoldMessenger.of(context)
..removeCurrentSnackBar()
..showSnackBar(SnackBar(content: Text('$result')));
}
}
class SelectionScreen extends StatelessWidget {
const SelectionScreen({super.key});
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('Pick an option'),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Padding(
padding: const EdgeInsets.all(8),
child: ElevatedButton(
onPressed: () {
// Close the screen and return "Yep!" as the result.
Navigator.pop(context, 'Yep!');
},
child: const Text('Yep!'),
),
),
Padding(
padding: const EdgeInsets.all(8),
child: ElevatedButton(
onPressed: () {
// Close the screen and return "Nope." as the result.
Navigator.pop(context, 'Nope.');
},
child: const Text('Nope.'),
),
)
],
),
),
);
}
}