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."), ) ); } }更多推荐
在应用程序主屏幕加载时自动显示警报对话框
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