flutter - 从无状态小部件调用到有状态小部件时，变量返回null吗？

Question

我有一张 map ，上面有这些labels。

final Map<int, int> labels = {
  1: 8,
  2: 24,
  3: 6,
  4: 12,
  5: 32,
  6: 2,
  7: 8,
  8: 77,
};

可以使用变量“selected”来调用

class Score extends StatelessWidget 
{
   final int selected;
   Score(this.selected);
   @override
   Widget build(BuildContext context) {
   return Text('You're score is ${labels[selected]}',
         style: TextStyle(
                fontStyle: FontStyle.normal,
                fontSize: 24.0,
                fontWeight: FontWeight.w500,
                color: Colors.white,
                fontFamily: "Netflix"));
   }
}

这与另一个类Card1中的 StreamBuilder连接，该类作为 Stateful小部件扩展为:

class Card1 extends StatefulWidget 
{
    @override
    Card1({Key key}) : super(key: key);
    Card1State createState() => Card1State();
}

class Card1State extends State<Card1> 
{  
    @override
    Widget build(BuildContext context) {
    return ... //other code,
    StreamBuilder(
              stream: _dividerController.stream,
              builder: (context, snapshot) => snapshot.hasData
              ? Score(snapshot.data)
              : Container(),
       ),
}

我的问题是我无法从 selected类调用 Score的值到 Card1类，并且它始终返回 null。

如何将选定的值称为 Card1类？

编辑:这是我的完整源代码

import 'dart:async';
import 'dart:math';
import 'package:flutter_spinning_wheel/flutter_spinning_wheel.dart';
import 'package:flutter/material.dart';

final Map<int, int> labels = {
  1: 8,
  2: 24,
  3: 6,
  4: 12,
  5: 32,
  6: 2,
  7: 8,
  8: 77,
};

class Card1 extends StatefulWidget {
  @override
  Card1({Key key}) : super(key: key);
  Card1State createState() => Card1State();
}

class Card1State extends State<Card1> {
  String spinReward;

  final StreamController _dividerController = StreamController<int>();
  final _wheelNotifier = StreamController<double>();

  double _generateRandomVelocity() => (Random().nextDouble() * 6000) + 2000;
  double _generateRandomAngle() => Random().nextDouble() * pi * 2;

  @override
  void dispose() {
    _dividerController.close();
    _wheelNotifier.close();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Material(
      child: Container(
        decoration: BoxDecoration(
          gradient: LinearGradient(
            colors: [const Color(0xFFFFFFF), const Color(0xFFFFFFF)],
            begin: Alignment.centerLeft,
            end: Alignment.centerRight,
          ),
        ),
        child: WillPopScope(
          onWillPop: () async {
            return true;
          },
          child: Scaffold(
            backgroundColor: Colors.transparent,
            body: Center(
              child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  SpinningWheel(
                    Image.asset('assets/app/Card1-8-300.png'),
                    width: 350,
                    height: 350,
                    initialSpinAngle: _generateRandomAngle(),
                    spinResistance: 0.6,
                    canInteractWhileSpinning: false,
                    dividers: 8,
                    onUpdate: _dividerController.add,
                    onEnd: _dividerController.add,
                    secondaryImage:
                        Image.asset('assets/app/Card1-center-300.png'),
                    secondaryImageHeight: 110,
                    secondaryImageWidth: 110,
                    shouldStartOrStop: _wheelNotifier.stream,
                  ),
                  SizedBox(height: 30),
                  StreamBuilder(
                    stream: _dividerController.stream,
                    builder: (context, snapshot) =>
                        snapshot.hasData ? Score(snapshot.data) : Container(),
                  ),
                  SizedBox(height: 20),
                  RaisedButton(
                    child: Text(
                      "SPIN NOW!",
                      textAlign: TextAlign.center,
                      style: TextStyle(
                        color: Colors.white,
                        fontSize: 18,
                        fontFamily: "Netflix",
                        fontWeight: FontWeight.bold,
                      ),
                    ),
                    color: Color(0xFFFE524B),
                    onPressed: () {
                      spinWheel();
                    },
                  ),
                ],
              ),
            ),
          ),
        ),
      ),
    );
  }

  spinWheel() {
    Timer(Duration(seconds: 5), () {
      //labels[selected] is null
      spinReward = "${labels[selected]}";
      print(spinReward);
    });
    _wheelNotifier.sink.add(_generateRandomVelocity());
  }
}

class Score extends StatelessWidget {
  //This is the value of selected I want to call in my other class
  final int selected;
  Score(this.selected);
  @override
  Widget build(BuildContext context) {
    return Container();
  }
}

Answer 1

在int selected中添加变量Card1State

class Card1State extends State<Card1> 
{  
    int selected;
}

创建 Score时设置选定的值

    @override
    Widget build(BuildContext context) {
    return ... //other code,
    StreamBuilder(
              stream: _dividerController.stream,
              builder: (context, snapshot) => snapshot.hasData
              ? Score(selected = snapshot.data)
              : Container(),
       ),