我无法使用AFNetworking取消下载。在我的应用中，用户可以通过这种方式触发单部电影下载:NSURLRequest*request=[NSURLRequestrequestWithURL:[NSURLURLWithString:urlString]];AFHTTPRequestOperation*operation=[[AFHTTPRequestOperationalloc]initWithRequest:request];[operationsetCompletionBlockWithSuccess:^(AFHTTPRequestOperation*operation,idre