Flutter setState() 对列表数据更改没有反应

Question

当我点击浮动按钮时，试图改变小部件，但没有成功，为什么？

List的元素数据确实发生了变化，但是widget并没有同步更新。

这个问题让我很困惑，不知道如何解决？ 我希望 ListView 小部件响应列表数据的变化。

主要.dart

import 'package:flutter/material.dart';

import 'video_model.dart';
import 'video_item.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  var videos = [
    VideoModel(title: 'a', intro: 'x'),
    VideoModel(title: 'b', intro: 'y'),
    VideoModel(title: 'c', intro: 'z'),
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      floatingActionButton: FloatingActionButton(
        child: const Icon(Icons.add),
        onPressed: () {
          setState(() {
            videos = [
              VideoModel(title: 'c', intro: 'o'),
              VideoModel(title: 'd', intro: 'p'),
              VideoModel(title: 'f', intro: 'q'),
            ];
          });
        },
      ),
      body: ListView.builder(
        shrinkWrap: true,
        physics: const ScrollPhysics(),
        itemCount: videos.length,
        itemBuilder: (context, index) {
          var video = videos[index];
          return VideoItem(video);
        },
      ),
    );
  }
}

video_item.dart

import 'package:flutter/material.dart';

import 'video_model.dart';

class VideoItem extends StatefulWidget {
  final VideoModel video;
  const VideoItem(this.video, {Key? key}) : super(key: key);

  @override
  State<VideoItem> createState() => _VideoItemState();
}

class _VideoItemState extends State<VideoItem> {
  late VideoModel video;

  @override
  void initState() {
    super.initState();
    video = widget.video;
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      padding: const EdgeInsets.all(16),
      child: Row(
        children: [
          Text(video.title),
          const SizedBox(width: 16),
          Text(video.intro)
        ],
      ),
    );
  }
}

video_model.dart

class VideoModel {
  String title;
  String intro;

  VideoModel({
    required this.title,
    required this.intro,
  });
}

Answer 1

在video_item.dart中，您在initState中设置了 video 变量，该变量仅运行一次，因此每当您使用setState时，只会再次调用build方法。 因此_VideoItemState中的video变量永远不会再次设置，因此它保持相同的旧值

您可以像这样简单地使用VideoItem构造函数中的视频

children: [
      Text(widget.video.title),
      const SizedBox(width: 16),
      Text(widget.video.intro)
    ],