有没有办法将下载进度侦听器添加到 CachedNetworkImage() 以在单独的小部件中显示 CircularProgressIndicator()？

如何解决有没有办法将下载进度侦听器添加到 CachedNetworkImage() 以在单独的小部件中显示 CircularProgressIndicator()？

我想在 CircularProgressIndicator() 内的 GridView.builder() 下添加带有加载指示的单独小部件，例如 SliverChildListDelegate()。因此，当用户向上拖动网格并加载新图像时，可以在底部观察加载状态指示器。很好的参考是查看 Instagram 图片网格，基本上它与加载指示器具有相同的行为。在我看来，为了实现该指标，我需要找到将侦听器绑定到 progressIndicatorBuilder 内的 downloadProgress 或 CachednetworkImage() 的方法，但我没有找到如何做到这一点。

可以在 GitHub

上找到带有代码的项目

pubspec.yaml 中使用的依赖项：

• http: any
• cached_network_image: ^3.0.0

代码：

import 'dart:convert';
import 'package:Flutter/foundation.dart';
import 'package:Flutter/material.dart';
import 'package:http/http.dart' as http;
import 'package:cached_network_image/cached_network_image.dart';

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

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

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  List list = [];
  var isLoading = false;
  List<String> images = [];
  int counter = 0;
  int totalNumberImages = 0;
  final _scrollController = new ScrollController();
  final _scrollController2 = new ScrollController();
  String customText = '';
  double textHeight = 0;

  _fetchData() async {
    setState(() {
      isLoading = true;
    });
    final response = await http
        .get(Uri.parse("https://dog.ceo/api/breed/hound/images/random/100"));
    if (response.statusCode == 200) {
      list = (json.decode(response.body)['message']);
      totalNumberImages = list.length;

      setState(() {
        isLoading = false;
        fetchTen();
      });
    } else {
      throw Exception('Failed to load photos');
    }
  }

  fetch() async {
    setState(() {
      images.add(list[counter]);
      counter++;
    });
  }

  fetchTen() {
    if (counter < totalNumberImages) {
      for (int i = 0; i < 10; i++) {
        fetch();
      }
    } else {
      setState(() {
        customText = "end of story :(";
        textHeight = 1.0;
        print("end of story :(");
      });
    }
  }

  @override
  void initState() {
    super.initState();
    print("initState");
    WidgetsBinding.instance.addPostFrameCallback((_) {
      _fetchData();
    });
    _scrollController2.addListener(() {
      if (_scrollController2.position.pixels ==
          _scrollController2.position.maxScrollExtent) {
        fetchTen();
      }
    });
  }

  @override
  void dispose() {
    _scrollController2.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: isLoading
          ? Center(
              child: CircularProgressIndicator(),)
          : GestureDetector(
              onVerticalDragStart: (details) {
                fetchTen();
              },child: CustomScrollView(
                controller: _scrollController2,slivers: [
                  SliverList(
                    delegate: SliverChildListDelegate(
                      [
                        GridView.builder(
                          shrinkWrap: true,gridDelegate:
                              SliverGridDelegateWithFixedCrossAxisCount(
                                  mainAxisspacing: 3.0,crossAxisspacing: 3.0,crossAxisCount: 3),controller: _scrollController,itemCount: images.length,itemBuilder: (BuildContext context,int index) {
                            return Container(
                              constraints:
                                  BoxConstraints.tightFor(height: 150.0),child: CachednetworkImage(
                                imageUrl: images[index],progressIndicatorBuilder:
                                    (context,url,downloadProgress) => Center(
                                  child: Container(
                                    color: Colors.grey[400],errorWidget: (context,error) =>
                                    Text('Error'),fit: BoxFit.cover,);
                          },Padding(
                          padding: const EdgeInsets.all(8.0),child: Center(
                            child: Text(
                              "$customText",style:
                                  TextStyle(height: textHeight,fontSize: 25),)
                      ],],);
  }
}