Flutter-setState不更新内部有状态小部件 [英] Flutter - setState not updating inner Stateful Widget

问题描述

基本上，我正在尝试制作一个应用程序，其内容将使用从网站获取信息的异步​​功能进行更新，但是当我尝试设置新状态时，它不会重新加载新内容。如果我调试了该应用程序，它将显示当前内容是新内容，但是在重建整个窗口小部件之后，它不会显示新信息。

Basically I am trying to make an app whose content will be updated with an async function that takes information from a website, but when I do try to set the new state, it doesn't reload the new content. If I debug the app, it shows that the current content is the new one, but after "rebuilding" the whole widget, it doesn't show the new info.

编辑：loadData（）方法，基本上读取带有http包的URL，该URL包含一个JSON文件，其内容每5分钟更新一次新消息。例如，带有体育实时记分板的.json文件的得分始终在变化，因此内容应始终随着新结果而变化。

loadData ( ) method, basically read a URL with http package, the URL contains a JSON file whose content changes every 5 minutes with new news. For example a .json file with sports real-time scoreboards whose scores are always changing, so the content should always change with new results.

class mainWidget extends StatefulWidget
{    
  State<StatefulWidget> createState() => new mainWidgetState();
}

class mainWidgetState extends State<mainWidget>
{

  List<Widget> _data;
  Timer timer;

  Widget build(BuildContext context) {
     return new ListView(
              children: _data);
  }

  @override
  void initState() {
    super.initState();
    timer = new Timer.periodic(new Duration(seconds: 2), (Timer timer) async {
      String s = await loadData();
      this.setState(() {
        _data = <Widget> [new childWidget(s)];
      });
      });
  }
}

class childWidget extends StatefulWidget {
  childWidget(String s){
    _title = s;
  }

  Widget _title;

  createState() => new childState();
}

class childState extends State<gameCardS> {

  Widget _title;

  @override
  Widget build(BuildContext context) {
    return new GestureDetector(onTap: foo(),
       child: new Card(child: new Text(_title));

  }

  initState()
  {
    super.initState();
    _title = widget._title;
  }
}

推荐答案

基本上，您总是希望在 build 方法层次结构中创建窗口小部件。

This should sort your problem out. Basically you always want your Widgets created in your build method hierarchy.

import 'dart:async';

import 'package:flutter/material.dart';

void main() => runApp(new MaterialApp(home: new Scaffold(body: new MainWidget())));

class MainWidget extends StatefulWidget {
    @override
    State createState() => new MainWidgetState();
}

class MainWidgetState extends State<MainWidget> {

    List<ItemData> _data = new List();
    Timer timer;

    Widget build(BuildContext context) {
        return new ListView(children: _data.map((item) => new ChildWidget(item)).toList());
    }

    @override
    void initState() {
        super.initState();
        timer = new Timer.periodic(new Duration(seconds: 2), (Timer timer) async {
            ItemData data = await loadData();
            this.setState(() {
                _data = <ItemData>[data];
            });
        });
    }


    @override
    void dispose() {
        super.dispose();
        timer.cancel();
    }

    static int testCount = 0;

    Future<ItemData> loadData() async {
        testCount++;
        return new ItemData("Testing #$testCount");
    }
}

class ChildWidget extends StatefulWidget {

    ItemData _data;

    ChildWidget(ItemData data) {
        _data = data;
    }

    @override
    State<ChildWidget> createState() => new ChildState();
}

class ChildState extends State<ChildWidget> {

    @override
    Widget build(BuildContext context) {
        return new GestureDetector(onTap: () => foo(),
            child: new Padding(
                padding: const EdgeInsets.symmetric(vertical: 12.0, horizontal: 24.0),
                child: new Card(
                    child: new Container(
                        padding: const EdgeInsets.all(8.0),
                        child: new Text(widget._data.title),
                    ),
                ),
            )
        );
    }

    foo() {
        print("Card Tapped: " + widget._data.toString());
    }
}

class ItemData {
    final String title;

    ItemData(this.title);

    @override
    String toString() {
        return 'ItemData{title: $title}';
    }
}

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