Flutter中网络图片加载和缓存源码分析（内存缓存

import 'dart:ui' as ui;
import 'package:flutter/foundation.dart';
import 'package:flutter/services.dart';
import 'package:flutter/widgets.dart';
 
class CachedNetworkImageProvider extends ImageProvider<CachedNetworkImageProvider> {
  final String url;
  final double scale;
 
  CachedNetworkImageProvider(this.url, {this.scale = 1.0});
 
  @override
  Future<CachedNetworkImageProvider> obtainKey(ImageConfiguration configuration) {
    return SynchronousFuture<CachedNetworkImageProvider>(this);
  }
 
  @override
  ImageStreamCompleter load(CachedNetworkImageProvider key) {
    final PaintingBinding binding = PaintingBinding.instance;
    final ImageStreamCompleter completer = ImageStreamCompleter();
 
    // 假设已经有方法`loadImageFromCache`从内存缓存中获取图片
    loadImageFromCache(url).then((ui.Image image) {
      binding.instantiateImageCodec(image.toByteData(format: ImageByteFormat.png))
        .then((ui.ImageDescriptor descriptor) {
          completer.setImage(descriptor);
        });
    });
 
    return completer;
  }
 
  @override
  bool operator ==(Object other) {
    if (other.runtimeType != runtimeType) {
      return false;
    }
    return other is CachedNetworkImageProvider
        && other.url == url
        && other.scale == scale;
  }
 
  @override
  int get hashCode => hashValues(url, scale);
}
 
// 假设的内存缓存图片的方法
Future<ui.Image> loadImageFromCache(String url) async {
  // 实现图片加载和缓存的逻辑
  // 返回ui.Image对象
}

这个示例代码展示了如何创建一个自定义的ImageProvider，用于从内存缓存中加载网络图片。loadImageFromCache方法是假设的，实际中你需要实现从内存缓存中加载图片的逻辑。这个示例旨在教导开发者如何在Flutter中实现自定义的图片加载逻辑。