在 flutter 中自动加载应用程序主屏幕上的显示警报对话框

Question

我想根据条件显示警报对话框。不基于用户交互，例如按钮按下事件。

如果在应用程序状态数据警报对话框中设置了标志，否则不会显示。

下面是我要显示的示例警报对话框

  void _showDialog() {
    // flutter defined function
    showDialog(
      context: context,
      builder: (BuildContext context) {
        // return object of type Dialog
        return AlertDialog(
          title: new Text("Alert Dialog title"),
          content: new Text("Alert Dialog body"),
          actions: <Widget>[
            // usually buttons at the bottom of the dialog
            new FlatButton(
              child: new Text("Close"),
              onPressed: () {
                Navigator.of(context).pop();
              },
            ),
          ],
        );
      },
    );
  }

我试图在主屏幕小部件的构建方法中调用该方法，但它给了我错误 -

 The context used to push or pop routes from the Navigator must be that of a widget that is a descendant of a Navigator widget.
E/flutter ( 3667): #0      Navigator.of.<anonymous closure> (package:flutter/src/widgets/navigator.dart:1179:9)
E/flutter ( 3667): #1      Navigator.of (package:flutter/src/widgets/navigator.dart:1186:6)
E/flutter ( 3667): #2      showDialog (package:flutter/src/material/dialog.dart:642:20)

问题是我不知道应该从哪里调用 _showDialog 方法？

Answer 1

您必须将内容包装在另一个 Widget（最好是无状态的）中。

示例：

更改自：

  import 'package:flutter/material.dart';

  void main() {
    runApp(new MyApp());
  }

  class MyApp extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
      return MaterialApp(
          title: 'Trial',
          home: Scaffold(
              appBar: AppBar(title: Text('List scroll')),
              body: Container(
                child: Text("Hello world"),
              )));
    }
  }

到这个：

  import 'dart:async';
  import 'package:flutter/material.dart';

  void main() {
    runApp(new MyApp());
  }

  class MyApp extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
      return MaterialApp(
          title: 'Trial',
          home: Scaffold(
              appBar: AppBar(title: Text('List scroll')), body: new MyHome()));
    }
  }

  class MyHome extends StatelessWidget { // Wrapper Widget
    @override
    Widget build(BuildContext context) {
      Future.delayed(Duration.zero, () => showAlert(context));
      return Container(
        child: Text("Hello world"),
      );
    }

    void showAlert(BuildContext context) {
      showDialog(
          context: context,
          builder: (context) => AlertDialog(
                content: Text("hi"),
              ));
    }
  }

注意：请参阅以在 Future.delayed(Duration.zero,..)

中包装 show alert

Answer 2

我会把它放在 State（StatefulWidget 的 initState 中。

将它放在 Stateless 小部件的 build 方法中很诱人，但这会多次触发您的警报。

在下面的示例中，当设备未连接到 Wifi 时显示警报，如果未连接则显示 [重试] 按钮。

import 'package:flutter/material.dart';
import 'package:connectivity/connectivity.dart';

void main() => runApp(MaterialApp(title: "Wifi Check", home: MyPage()));

class MyPage extends StatefulWidget {
    @override
    _MyPageState createState() => _MyPageState();
}

class _MyPageState extends State<MyPage> {
    bool _tryAgain = false;

    @override
    void initState() {
      super.initState();
      _checkWifi();
    }

    _checkWifi() async {
      // the method below returns a Future
      var connectivityResult = await (new Connectivity().checkConnectivity());
      bool connectedToWifi = (connectivityResult == ConnectivityResult.wifi);
      if (!connectedToWifi) {
        _showAlert(context);
      }
      if (_tryAgain != !connectedToWifi) {
        setState(() => _tryAgain = !connectedToWifi);
      }
    }

    @override
    Widget build(BuildContext context) {
      var body = Container(
        alignment: Alignment.center,
        child: _tryAgain
          ? RaisedButton(
              child: Text("Try again"),
              onPressed: () {
                _checkWifi();
            })
          : Text("This device is connected to Wifi"),
      );

      return Scaffold(
        appBar: AppBar(title: Text("Wifi check")),
        body: body
      );
    }

    void _showAlert(BuildContext context) {
      showDialog(
          context: context,
          builder: (context) => AlertDialog(
            title: Text("Wifi"),
            content: Text("Wifi not detected. Please activate it."),
          )
      );
    }
}

Answer 3

我使用 Flutter 社区开发的包解决了它。这里 https://pub.dev/packages/after_layout

将此添加到您的 pubspec.yaml

after_layout: ^1.0.7+2

然后试试下面的例子

import 'package:after_layout/after_layout.dart';
import 'package:flutter/material.dart';

class DialogDemo extends StatefulWidget {
  @override
  _DialogDemoState createState() => _DialogDemoState();
}

class _DialogDemoState extends State<DialogDemo>
    with AfterLayoutMixin<DialogDemo> {
  @override
  void initState() {
    super.initState();
  }

  @override
  void afterFirstLayout(BuildContext context) {
    _neverSatisfied();
  }

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: Container(
        decoration: BoxDecoration(color: Colors.red),
      ),
    );
  }

  Future<void> _neverSatisfied() async {
    return showDialog<void>(
      context: context,
      barrierDismissible: false, // user must tap button!
      builder: (BuildContext context) {
        return AlertDialog(
          title: Text('Rewind and remember'),
          content: SingleChildScrollView(
            child: ListBody(
              children: <Widget>[
                Text('You will never be satisfied.'),
                Text('You\’re like me. I’m never satisfied.'),
              ],
            ),
          ),
          actions: <Widget>[
            FlatButton(
              child: Text('Regret'),
              onPressed: () {
                Navigator.of(context).pop();
              },
            ),
          ],
        );
      },
    );
  }
}

Answer 4

只需覆盖 initState 并在 Future 或 Timer:

中调用您的 _showDialog 方法

@override
void initState() {
  super.initState();

  // Use either of them. 
  Future(_showDialog);
  Timer.run(_showDialog); // Requires import: 'dart:async'
}

Answer 5

这就是我如何以简单的方式实现的：

添加https://pub.dev/packages/shared_preferences

在主屏幕（或任何所需的小部件）的构建方法上方：

Future checkFirstRun(BuildContext context) async {
 SharedPreferences prefs = await SharedPreferences.getInstance();
 bool isFirstRun = prefs.getBool('isFirstRun') ?? true;

 if (isFirstRun) {
   // Whatever you want to do, E.g. Navigator.push()
   prefs.setBool('isFirstRun', false);
 } else {
   return null;
 }
}

然后在您的小部件的 initState 上：

@override
void initState() {
  super.initState();
  WidgetsBinding.instance.addPostFrameCallback((_) => checkFirstRun(context));
}

这确保了构建小部件后函数是运行。

Answer 6

如果您使用的是 bloc，则按照@mirkancal 在此答案中的建议使用 BlocListener：

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