flutter - Flutter:针对整个应用程序的SnackBar方法，修改Scaffold以跟踪当前显示的Scaffolds的BuildContext

我正在尝试跟踪当前的Scaffold(它们的BuildContext)，以创建一个应用程序范围的SnackBar函数。当前，我正在创建一个class，它显示一个Scaffold并将其context添加到另一个class，后者管理当前正在运行的Scaffold。但是，我没有成功，因为我目前的尝试有两个问题:

不能正确存储当前Scaffold的

显然，对于从当前dispose的Scaffold的BuildContext中删除List的Scaffold而言，BuildContext方法为时已晚，因此向我展示了Exception，“Looking up a deactivated widget's ancestor is unsafe.”

这是我目前的尝试:

实现(main.dart):

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

import 'MScaffold.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Snackbar manager',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Snackbar manager'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return MScaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(),
      floatingActionButton: Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          FloatingActionButton(
            heroTag: 0,
            child:Icon(Icons.add_circle_outline),
            onPressed: (){
              MScaffoldManager.showSnackbar();
            },
          ),
          FloatingActionButton(
            heroTag: 1,
            child:Icon(Icons.remove_circle_outline),
            onPressed: (){
              MScaffoldManager.hideSnackbar();
            },
          ),
          FloatingActionButton(
            heroTag: 2,
            child:Icon(Icons.add),
            onPressed: (){
              Navigator.of(context).push(
                MaterialPageRoute(
                  builder: (context){
                    return SecondScaffold();
                  }
                )
              );
            },
          ),
        ],
      ),
    );
  }
}

class SecondScaffold extends StatelessWidget{
  @override
  Widget build(BuildContext context){
    return MScaffold(
      appBar: AppBar(
        title: Text("Page 2"),
      ),
      body: Center(),
      floatingActionButton: Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          FloatingActionButton(
            heroTag: 0,
            child:Icon(Icons.add_circle_outline),
            onPressed: (){
              MScaffoldManager.showSnackbar();
            },
          ),
          FloatingActionButton(
            heroTag: 1,
            child:Icon(Icons.remove_circle_outline),
            onPressed: (){
              MScaffoldManager.hideSnackbar();
            },
          ),
          FloatingActionButton(
            heroTag: 2,
            child:Icon(Icons.remove),
            onPressed: (){
              Navigator.of(context).pop();
            },
          ),
        ],
      ),
    );
  }
}

library class es:MScaffoldManager; MScaffold;和MScaffoldState:

import 'package:flutter/cupertino.dart';
import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';

class MScaffoldManager{
  static List<Map> scaffoldInformation = List();
  static void addScaffold(context){
    scaffoldInformation.add({'context':context});
    print("Scaffold added:\n"+scaffoldInformation.toString());
  }
  static void removeScaffold(context){
    Scaffold.of(context).hideCurrentSnackBar();
    scaffoldInformation.remove({'context':context});
    print("Scaffold removed:\n"+scaffoldInformation.toString());
  }
  static void showSnackbar(){
    scaffoldInformation.forEach((v){
      Scaffold.of(v['context']).showSnackBar(SnackBar(
        content: Text("Snackbar works"),
      ));
    });
  }
  static void hideSnackbar(){
    scaffoldInformation.forEach((v){
      Scaffold.of(v['context']).hideCurrentSnackBar();
    });
  }
}


class MScaffold extends StatefulWidget{
  Key key;
  var appBar;
  var body;
  var floatingActionButton;
  var floatingActionButtonLocation;
  var floatingActionButtonAnimator;
  var persistentFooterButtons;
  var drawer;
  var endDrawer;
  var bottomNavigationBar;
  var bottomSheet;
  var backgroundColor;
  var resizeToAvoidBottomPadding;
  var resizeToAvoidBottomInset;
  var primary;
  var drawerDragStartBehavior;
  var extendBody;
  var extendBodyBehindAppBar;
  var drawerScrimColor;
  var drawerEdgeDragWidth;

  MScaffold({
    Key key,
    this.appBar,
    this.body,
    this.floatingActionButton,
    this.floatingActionButtonLocation,
    this.floatingActionButtonAnimator,
    this.persistentFooterButtons,
    this.drawer,
    this.endDrawer,
    this.bottomNavigationBar,
    this.bottomSheet,
    this.backgroundColor,
    this.resizeToAvoidBottomPadding,
    this.resizeToAvoidBottomInset,
    this.primary = true,
    this.drawerDragStartBehavior = DragStartBehavior.start,
    this.extendBody = false,
    this.extendBodyBehindAppBar = false,
    this.drawerScrimColor,
    this.drawerEdgeDragWidth,
  })  : assert(primary != null),
      assert(extendBody != null),
      assert(extendBodyBehindAppBar != null),
      assert(drawerDragStartBehavior != null);

  @override
  State<StatefulWidget> createState() {
    return MScaffoldState(
      key: key,
      appBar: appBar,
      body: body,
      floatingActionButton: floatingActionButton,
      floatingActionButtonLocation: floatingActionButtonLocation,
      floatingActionButtonAnimator: floatingActionButtonAnimator,
      persistentFooterButtons: persistentFooterButtons,
      drawer: drawer,
      endDrawer: endDrawer,
      bottomNavigationBar: bottomNavigationBar,
      bottomSheet: bottomSheet,
      backgroundColor: backgroundColor,
      resizeToAvoidBottomPadding: resizeToAvoidBottomPadding,
      resizeToAvoidBottomInset: resizeToAvoidBottomInset,
      primary: primary,
      drawerDragStartBehavior: drawerDragStartBehavior,
      extendBody: extendBody,
      extendBodyBehindAppBar: extendBodyBehindAppBar,
      drawerScrimColor: drawerScrimColor,
      drawerEdgeDragWidth: drawerEdgeDragWidth,
    );
  }

}

class MScaffoldState extends State<MScaffold> {
  Key key;
  var appBar;
  var body;
  var floatingActionButton;
  var floatingActionButtonLocation;
  var floatingActionButtonAnimator;
  var persistentFooterButtons;
  var drawer;
  var endDrawer;
  var bottomNavigationBar;
  var bottomSheet;
  var backgroundColor;
  var resizeToAvoidBottomPadding;
  var resizeToAvoidBottomInset;
  var primary;
  var drawerDragStartBehavior;
  var extendBody;
  var extendBodyBehindAppBar;
  var drawerScrimColor;
  var drawerEdgeDragWidth;

  MScaffoldState({
    Key key,
    this.appBar,
    this.body,
    this.floatingActionButton,
    this.floatingActionButtonLocation,
    this.floatingActionButtonAnimator,
    this.persistentFooterButtons,
    this.drawer,
    this.endDrawer,
    this.bottomNavigationBar,
    this.bottomSheet,
    this.backgroundColor,
    this.resizeToAvoidBottomPadding,
    this.resizeToAvoidBottomInset,
    this.primary = true,
    this.drawerDragStartBehavior = DragStartBehavior.start,
    this.extendBody = false,
    this.extendBodyBehindAppBar = false,
    this.drawerScrimColor,
    this.drawerEdgeDragWidth,
  })  : assert(primary != null),
      assert(extendBody != null),
      assert(extendBodyBehindAppBar != null),
      assert(drawerDragStartBehavior != null);

  @override
  void initState() {
    super.initState();
  }
  @override
  dispose(){
    MScaffoldManager.removeScaffold(_scaffoldContext);
    super.dispose();

  }
  BuildContext _scaffoldContext;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: key,
      appBar: appBar,
      body: Builder(
        builder: (context){
          if(_scaffoldContext!=null)
            MScaffoldManager.removeScaffold(_scaffoldContext);
          _scaffoldContext = context;
          MScaffoldManager.addScaffold(_scaffoldContext);
          return body;
        },
      ),
      floatingActionButton: floatingActionButton,
      floatingActionButtonLocation: floatingActionButtonLocation,
      floatingActionButtonAnimator: floatingActionButtonAnimator,
      persistentFooterButtons: persistentFooterButtons,
      drawer: drawer,
      endDrawer: endDrawer,
      bottomNavigationBar: bottomNavigationBar,
      bottomSheet: bottomSheet,
      backgroundColor: backgroundColor,
      resizeToAvoidBottomPadding: resizeToAvoidBottomPadding,
      resizeToAvoidBottomInset: resizeToAvoidBottomInset,
      primary: primary,
      drawerDragStartBehavior: drawerDragStartBehavior,
      extendBody: extendBody,
      extendBodyBehindAppBar: extendBodyBehindAppBar,
      drawerScrimColor: drawerScrimColor,
      drawerEdgeDragWidth: drawerEdgeDragWidth,
    );
  }
}

承认它不能按原样工作，它似乎也有些冗长和困惑。我想做的就是简单地制作一个Scaffold class，其功能类似于Scaffold，但是与管理器class一起使用，它可以跟踪所有Scaffold的context，因此无论什么页面，我都可以轻松显示SnackBar消息用户开启。

最佳答案

我还没有亲自尝试过此代码，但是您如何创建要与ChangeNotifier一起使用的Provider并将其附加在MaterialApp上方:

class MyErrorChangeNotifier extends ChangeNotifier {
  String error;

  setError(String error) {
    this.error = error;

    notifyListeners();
  }
}

然后创建一个自定义的Scaffold，如果已安装SnackBar，则每次调用setError时都会显示Scaffold:

class MyScaffold extends Scaffold {
  // TODO constructor

  @override
  ScaffoldState createState() => MyScaffoldState();
}

class MyScaffoldState extends ScaffoldState {
  MyErrorChangeNotifier _myErrorCN;
  Function() _listener;

  @override
  void initState() {
    super.initState();

    _listener = () {
      if (mounted) {
        showSnackBar(SnackBar(content: Text(_myErrorCN.error)));
      }
    };

    Future.microtask(() {
      _myErrorCN = Provider.of<MyErrorChangeNotifier>(context, listen: false)..addListener(_listener);
    });
  }

  @override
  void dispose() {
    _myErrorCN?.removeListener(_listener);

    super.dispose();
  }
}

每当有这种使用案例时，请尝试使用提供程序考虑解决方案-将数据从上下文层次结构发送到ChangeNotifier，ChangeNotifier然后将数据从上下文层次结构发送回所有侦听它的小部件。