在 Flutter 中按下后退按钮时关闭导航抽屉

Question

我的第一个 flutter 应用程序中有一个材质设计的导航抽屉。 这项工作很好，但如果在使用WillPopScope显示AlertDialog时它WillPopScope打开状态，我没有找到任何方法来关闭后退按钮按下时的导航抽屉。 该应用程序只显示AlertDialog而不是在按下后关闭抽屉。 如果已经打开，我希望抽屉应该关闭，否则显示AlertDialog 。

@override
Widget build(BuildContext context) {
  return WillPopScope(
    onWillPop: onBackPressed,
    child: Scaffold(
      appBar: AppBar(
        title: Text("Home"),
      ),
      drawer: Drawer(
      ),
      body: Center(
        child: Text("Home"),
      ),
    ),
  );
}

onBackPressed显示关闭应用程序的对话框。

Future<bool> onBackPressed() {
  return showDialog(
      barrierDismissible: false,
      context: context,
      builder: (context) => AlertDialog(
            title: Text("Do you want to exit?"),
            actions: <Widget>[
              FlatButton(
                  onPressed: () => Navigator.pop(context, false),
                  child: Text("No")),
              FlatButton(
                  onPressed: () => Navigator.pop(context, true),
                  child: Text("Yes"))
            ],
          ));
}

任何人都可以指导我如何实现这一目标？

Answer 1

您可以在下面复制粘贴运行完整代码
第 1 步：您需要 Scaffold 键来控制 Drawer，因此您需要GlobalKey<ScaffoldState> _key = new GlobalKey<ScaffoldState>();
第 2 步：在onWillPop您可以检查isDrawerOpen并执行Navigator.pop

代码片段

 GlobalKey<ScaffoldState> _key = new GlobalKey<ScaffoldState>();

  MyHomePage({Key key, this.title}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: () async {
        if (_key.currentState.isDrawerOpen) {
          Navigator.of(context).pop();
          return false;
        }
        return true;
      },
      child: Scaffold(

工作演示

完整代码

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: () async {
        print("My App Page");
        //return false;
      },
      child: MaterialApp(
        title: 'Flutter Demo',
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: MyHomePage(title: "test",),
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final String title;
  GlobalKey<ScaffoldState> _key = new GlobalKey<ScaffoldState>();

  MyHomePage({Key key, this.title}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: () async {
        if (_key.currentState.isDrawerOpen) {
          Navigator.of(context).pop();
          return false;
        }
        return true;
      },
      child: Scaffold(
        key: _key,
        appBar: AppBar(title: Text(title)),
        body: Center(child: Text('My Page!')),
        drawer: Drawer(
          child: ListView(
            padding: EdgeInsets.zero,
            children: <Widget>[
              DrawerHeader(
                child: Text('Drawer Header'),
                decoration: BoxDecoration(
                  color: Colors.blue,
                ),
              ),
              ListTile(
                title: Text('page 2'),
                onTap: () {
                  Navigator.push(
                      context, new MaterialPageRoute(builder: (context) => Page2()));
                },
              ),
              ListTile(
                title: Text('Item 2'),
                onTap: () {
                  // Update the state of the app
                  // ...
                  // Then close the drawer
                  Navigator.pop(context);
                },
              ),
            ],
          ),
        ),
      ),
    );
  }
}


class Page2 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: () async {
        print("Page2");
        _popNavigationWithResult(context, 'from_back');
        return false;
      },
      child: Scaffold(
        floatingActionButton: FloatingActionButton(
          onPressed: () {
            _popNavigationWithResult(context, 'from_button');
          },
        ),
        body: Container(
          child: Center(
            child: Text('Page 2',
                style: TextStyle(fontSize: 30.0, fontWeight: FontWeight.bold)),
          ),
        ),
      ),
    );
  }

  void _popNavigationWithResult(BuildContext context, dynamic result) {
    Navigator.pop(context, result);
  }
}