从有状态小部件更新无状态小部件

Question

主要.dart：

import 'package:flutter/material.dart';
import 'package:mypackage/widgets/home_widget.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "My App",
      theme: ThemeData(primarySwatch: Colors.blueGrey),
      home: Home(),
    );
  }
}

主页.dart：

import 'package:flutter/material.dart';
import 'package:mypackage/widgets/secondary_page.dart';
import 'package:mypackage/widgets/home_view.dart';
import 'package:mypackage/widgets/settings_page.dart';

class Home extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _HomeState();
  }
}

class _HomeState extends State<Home> {
  int currentPageIndex = 0;
  final List<Widget> pageWidgets = [HomeView(), SecondaryPage(), SettingsPage()];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("My App"),
          centerTitle: true,
        ),
        body: pageWidgets[currentPageIndex],
        bottomNavigationBar: BottomNavigationBar(
          onTap: onTabTapped,
          currentIndex: currentPageIndex,
          items: [
            BottomNavigationBarItem(
                icon: new Icon(Icons.home), label: "Tab One"),
            BottomNavigationBarItem(
                icon: new Icon(Icons.account_balance), label: "Tab Two"),
            BottomNavigationBarItem(
                icon: new Icon(Icons.settings), label: "Tab Three"),
          ],
        ),
        floatingActionButton: FloatingActionButton(onPressed: () {
          // Update data from here
          HomeView().updateDisplay();
        }));
  }

  // Changes the index when the tapped page has loaded
  void onTabTapped(int index) {
    setState(() {
      currentPageIndex = index;
    });
  }
}

HomeView.dart：

import 'package:flutter/material.dart';
import 'package:mypackage/models/mydisplay.dart';
import 'package:mypackage/network/mydata.dart';

class HomeView extends StatelessWidget {
  final List<MyDisplay> dataList = [
    new MyDisplay("Sample Display",
        "SampleFile", 0),
  ];

  Future<void> updateDisplay() async {
    MyData myData = new MyData();

    dataList.forEach((d) async {
      d.changePercentage = await myData
          .getDataPercentage("assets/data/" + d.fileName + ".xml");

      print(d.dataName +
          " change percentage: " +
          d.changePercentage.toString() +
          "%");
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: new ListView.builder(
          itemCount: dataList.length,
          itemBuilder: (BuildContext context, int index) =>
              buildCard(context, index)),
    );
  }

  Widget buildCard(BuildContext context, int index) {
    return Container(
        child: Card(
            color: Colors.teal.shade200,
            child: Padding(
                padding: const EdgeInsets.all(25),
                child: Column(children: <Widget>[
                  Text(dataList[index].dataName,
                      style: new TextStyle(
                          fontSize: 20, fontWeight: FontWeight.bold)),
                  Text(dataList[index].changePercentage.toString() + "%")
                ]))));
  }
}

当我从 floatActionButton 调用 updateDisplay() 方法时，它按预期工作，数据被打印到控制台，但是它似乎没有更新实际的 UI、卡片的内容，它们只是保持其初始设置值。

澄清一下：如何从有状态小部件更新列表视图（无状态小部件内）内的卡片内容？

如果这是一个重复的问题，我很抱歉，我已经查看并正在继续寻找问题的答案，但我根本无法让它工作。

Answer 1

您需要使用有状态小部件，因为您无法更新无状态小部件。查看此链接以获取更多信息。调用它的下一个问题可以通过使用 globalKeys 来解决。唯一奇怪的是你必须将 Home 有状态小部件和 HomeView 有状态小部件保存在同一个 dart 文件中。。尝试此代码以使其工作。

主页视图

import 'package:flutter/material.dart';
import 'package:mypackage/widgets/secondary_page.dart';
import 'package:mypackage/widgets/settings_page.dart';
import 'package:mypackage/models/mydisplay.dart';
import 'package:mypackage/network/mydata.dart';

class Home extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _HomeState();
  }
}

class _HomeState extends State<Home> {
  int currentPageIndex = 0;
  final List<Widget> pageWidgets = [HomeView(), SecondaryPage(), SettingsPage()];
  GlobalKey<_HomeViewState> _myKey = GlobalKey();// We declare a key here
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("My App"),
          centerTitle: true,
        ),
        body: pageWidgets[currentPageIndex],
        bottomNavigationBar: BottomNavigationBar(
          onTap: onTabTapped,
          currentIndex: currentPageIndex,
          items: [
            BottomNavigationBarItem(
                icon: new Icon(Icons.home), label: "Tab One"),
            BottomNavigationBarItem(
                icon: new Icon(Icons.account_balance), label: "Tab Two"),
            BottomNavigationBarItem(
                icon: new Icon(Icons.settings), label: "Tab Three"),
          ],
        ),
        floatingActionButton: FloatingActionButton(onPressed: () {
          // Update data from here
          _myKey.currentState.updateDisplay();//This is how we call the function
        }));
  }

  // Changes the index when the tapped page has loaded
  void onTabTapped(int index) {
    setState(() {
      currentPageIndex = index;
    });
  }
}

class HomeView extends StatefulWidget {
  Function updateDisplay;
  HomeView({Key key}): super(key: key);//This key is what we use
  @override
  _HomeViewState createState() => _HomeViewState();
}

class _HomeViewState extends State<HomeView> {
  final List<MyDisplay> dataList = [
    new MyDisplay("Sample Display",
        "SampleFile", 0),
  ];

@override
  void initState(){
    super.initState();
    widget.updateDisplay = () async {
      MyData myData = new MyData();

      dataList.forEach((d) async {
        d.changePercentage = await myData
            .getDataPercentage("assets/data/" + d.fileName + ".xml");
        print(d.dataName +
            " change percentage: " +
            d.changePercentage.toString() +
            "%");
      });
      setState((){});//This line rebuilds the scaffold
    };
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: new ListView.builder(
          itemCount: dataList.length,
          itemBuilder: (BuildContext context, int index) =>
              buildCard(context, index)),
    );
  }

  Widget buildCard(BuildContext context, int index) {
    return Container(
        child: Card(
            color: Colors.teal.shade200,
            child: Padding(
                padding: const EdgeInsets.all(25),
                child: Column(children: <Widget>[
                  Text(dataList[index].dataName,
                      style: new TextStyle(
                          fontSize: 20, fontWeight: FontWeight.bold)),
                  Text(dataList[index].changePercentage.toString() + "%")
                ]))));
  }
}

我们使用 setState((){}) 来重建小部件。只要记住一个想法即可。无论您在何处使用 updateDisplay 方法，都不要使其在重建后循环运行。例如。您可以在孩子体内的未来构建器中使用它。这样它就会不断重建

编辑

我们向 HomeView 添加了一个键，现在我们可以像 一样使用该键_myKey.currentState.yourFunction。希望我有帮助