在应用程序主屏幕加载时自动显示警报对话框 [英] Show alert dialog on app main screen load automatically in flutter

问题描述

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.

I want to show alert dialog based on a condition. Not based on user interaction such as button press event.

如果在应用状态数据警报对话框中设置了标志，否则不会显示.

If a flag is set in app state data alert dialog is shown otherwise its not.

下面是我想显示的示例警报对话框

Below is the sample alert dialog which I want to show

  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 -

I tried to call that method inside main screen widget's build method but it gives me error -

 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?

Problem is I don't know from where I should call that _showDialog method?

推荐答案

我会把它放在 State(StatefulWidget).

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.

Placing it in the build method of a Stateless widget is tempting, but that will trigger your alert multiple times.

在下面的这个例子中，当设备没有连接到 Wifi 时它会显示一个警报，如果没有连接到，则显示一个 [再试一次] 按钮.

In this example below, it displays an alert when the device is not connected to the Wifi, showing a [try again] button if it's not.

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."),
          )
      );
    }
}

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