即使实现了后退按钮关闭，它也不起作用

Question

即使我实现了后退按钮应用程序关闭。如果您按下返回按钮，则不会出现任何消​​息，您将返回登录屏幕。

主页正在主屏幕中运行。 为了找出任何可能的错误，我在两个地方都放了后退按钮关闭代码。

我不知道出了什么问题。

我需要帮助。

主屏幕

class HomeScreen extends StatelessWidget {
  DateTime currentBackPressTime;

  final scaffoldKey = GlobalKey<ScaffoldState>();

  final FirebaseUser user;
  HomeScreen({this.user});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Custom Navigation Drawer Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      debugShowCheckedModeBanner: false,
      home: WillPopScope(
        onWillPop: () async {
          bool result = onPressBackButton();
          return await Future.value(result);
        },
        child: MyHomePage(),
      ),
    );
  }

  bool onPressBackButton() {
    DateTime now = DateTime.now();
    if (currentBackPressTime == null ||
        now.difference(currentBackPressTime) > Duration(seconds: 2)) {
      currentBackPressTime = now;
      scaffoldKey.currentState
        ..hideCurrentSnackBar()
        ..showSnackBar(SnackBar(
          content: Text("Tap back again to leave."),
        ));
      return false;
    }
    return true;
  }

}

  class MyHomePage extends StatelessWidget {

    @override
    Widget build(BuildContext context) {
      return MaterialApp(
          debugShowCheckedModeBanner: false,
          theme: ThemeData(
              scaffoldBackgroundColor: Colors.white,
              primaryColor: Colors.white
          ),
          home: SideBarLayout(),
      );
    }
  }

主屏幕

import 'package:flutter/material.dart';
import 'package:aciel_pro/navigation_bloc/navigation_bloc.dart';


class Home extends StatelessWidget {
  DateTime currentBackPressTime;

  final scaffoldKey = GlobalKey<ScaffoldState>();


  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Custom Navigation Drawer Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      debugShowCheckedModeBanner: false,
      home: WillPopScope(
        onWillPop: () async {
          bool result = onPressBackButton();
          return await Future.value(result);
        },
        child: HomePage(),
      ),
    );
  }

  bool onPressBackButton() {
    DateTime now = DateTime.now();
    if (currentBackPressTime == null ||
        now.difference(currentBackPressTime) > Duration(seconds: 2)) {
      currentBackPressTime = now;
      scaffoldKey.currentState
        ..hideCurrentSnackBar()
        ..showSnackBar(SnackBar(
          content: Text("Tap back again to leave."),
        ));
      return false;
    }
    return true;
  }

}



class HomePage extends StatelessWidget with NavigationStates {
  BuildContext ctx;


  @override
  Widget build(BuildContext context) {
    ctx = context;

    return Scaffold(
        body: Center(
          child: Column(
          children: <Widget>[
            FlatButton(
              child: Text('예약하기',style: TextStyle(fontSize: 40)),
              onPressed: () =>showMessage('예약하기'),
              color:Colors.green,
              textColor: Colors.white,
            )
          ],
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        ),
        ),
    );
  }

  void showMessage(String msg) {
    final snackbar = SnackBar(content: Text(msg));

    Scaffold.of(ctx)
      ..removeCurrentSnackBar()
      ..showSnackBar(snackbar);
  }
}

Answer 1

您可以在下面复制粘贴运行完整代码
第 1 步：将final scaffoldKey = GlobalKey<ScaffoldState>(); 移出Home
第二步：添加Scaffold key

return Scaffold(
      key: scaffoldKey,

第 3 步：showMessage() 使用 scaffoldKey

scaffoldKey.currentState
  ..removeCurrentSnackBar()
  ..showSnackBar(snackbar);

工作演示

完整代码

import 'package:flutter/material.dart';

void main() {
  runApp(Home());
}

final scaffoldKey = GlobalKey<ScaffoldState>();

class Home extends StatelessWidget {
  DateTime currentBackPressTime;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Custom Navigation Drawer Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      debugShowCheckedModeBanner: false,
      home: WillPopScope(
        onWillPop: () async {
          bool result = onPressBackButton();
          return await Future.value(result);
        },
        child: HomePage(),
      ),
    );
  }

  bool onPressBackButton() {
    DateTime now = DateTime.now();
    if (currentBackPressTime == null ||
        now.difference(currentBackPressTime) > Duration(seconds: 2)) {
      currentBackPressTime = now;
      scaffoldKey.currentState
        ..hideCurrentSnackBar()
        ..showSnackBar(SnackBar(
          content: Text("Tap back again to leave."),
        ));
      return false;
    }
    return true;
  }
}

class HomePage extends StatelessWidget {
  BuildContext ctx;

  @override
  Widget build(BuildContext context) {
    ctx = context;

    return Scaffold(
      key: scaffoldKey,
      body: Center(
        child: Column(
          children: <Widget>[
            FlatButton(
              child: Text('예약하기', style: TextStyle(fontSize: 40)),
              onPressed: () => showMessage('예약하기'),
              color: Colors.green,
              textColor: Colors.white,
            )
          ],
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        ),
      ),
    );
  }

  void showMessage(String msg) {
    final snackbar = SnackBar(content: Text(msg));

    scaffoldKey.currentState
      ..removeCurrentSnackBar()
      ..showSnackBar(snackbar);
  }
}