Flutter StatefulWidget 不更新数据

Question

I am trying to pass a Map to a stateful widget, and the map updates from time to time. In my parent widget I call setState() when I change the data, and in the subwidget, I can see the data come across, but then if I try to use the data, it has not been updated. Any ideas why this might be, and how to fix it?

class AccountMenuWidgetState extends State {
  final Function _closeAccountMenu;
  final Function _signOut;
  String _accountToken;
  Map _userInfo;
  AccountMenuWidgetState(this._closeAccountMenu, this._signOut, this._accountToken, this._userInfo) {
    //_openAnimation();
    print("DEBUG2 " + _userInfo.toString());    <----- This shows the updated data
  }


      @override
      Widget build(BuildContext context){
        return Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
               _userInfo.toString(),                  <------ This does not update with new data
               style: TextStyle(color: Colors.red),
            ), 
          ],
        );
      }

Answer 1

Please check the following code snippet, Inside State, you need to use widget._userInfo
Skeleton of a stateful widget, you can see https://api.flutter.dev/flutter/widgets/StatefulWidget-class.html
You can copy paste and run full code below

code snippet

AccountMenuWidget(null, null, "test", {"ab": "cd"}),
...

class AccountMenuWidget extends StatefulWidget {
  final Function _closeAccountMenu;
  final Function _signOut;
  String _accountToken;
  Map _userInfo;
  AccountMenuWidget(this._closeAccountMenu, this._signOut, this._accountToken,
      this._userInfo) {
    //_openAnimation();
    print("DEBUG2 " + _userInfo.toString());
  }

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

class _AccountMenuWidgetState extends State<AccountMenuWidget> {
  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        Text(
          widget._userInfo.toString(),
          style: TextStyle(color: Colors.red),
        ),
      ],
    );
  }
}

full code

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            AccountMenuWidget(null, null, "test", {"ab": "cd"}),
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

class AccountMenuWidget extends StatefulWidget {
  final Function _closeAccountMenu;
  final Function _signOut;
  String _accountToken;
  Map _userInfo;
  AccountMenuWidget(this._closeAccountMenu, this._signOut, this._accountToken,
      this._userInfo) {
    //_openAnimation();
    print("DEBUG2 " + _userInfo.toString());
  }

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

class _AccountMenuWidgetState extends State<AccountMenuWidget> {
  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        Text(
          widget._userInfo.toString(),
          style: TextStyle(color: Colors.red),
        ),
      ],
    );
  }
}

Output

I/flutter (15801): DEBUG2 {ab: cd}