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。

如果在应用状态数据警报对话框中设置了标志，则显示否则，则不显示。

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build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)

问题是我不知道从哪里调用该_showDialog方法？

Answer 1

只需覆盖SELECT Product, Event_Type, Quantity FROM Purchasing GROUP BY 1,2;并在initState内调用您的_showDialog方法

Timer.run()

Answer 2

您必须将内容包装在另一个Widget（最好是无状态）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"),
              )));
    }
  }

为此：

  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：有关将显示警报包装在Future.delayed(Duration.zero,..)中的信息，请参见here

Answer 3

我将其放置在initState的{{1}}的{{1}}中。

将其放在State小部件的StatefulWidget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，它将显示警报，如果未连接，则显示[重试]按钮。

build

Answer 4

这就是我以一种简单的方式实现这一目标的方法：

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：

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;
 }
}

然后在小部件的initState上

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

这可确保在构建窗口小部件后运行该功能。

Answer 5

如果您使用的是 blocs，请使用 @mirkancal 在此答案中建议的 BlocListener：Flutter: bloc, how to show an alert dialog

Answer 6

我使用Flutter Community开发的软件包解决了它。这里https://pub.dev/packages/after_layout

将此添加到您的pubspec.yaml

after_layout: ^1.0.7+2

并尝试以下示例

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();
              },
            ),
          ],
        );
      },
    );
  }
}

在应用程序主屏幕上显示警报对话框会自动在抖动中加载

6 个答案: