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iOS 7之后，URLSession成为替代NSURLConnection的标准网络接口，两者在功能上具有相似的特性。然而，URLSession在资源管理和后台操作方面展现出显著优势。特别是在流行的第三方框架AFNetworking中，URLSession的集成更加完善，为开发者提供了更高效的网络管理解决方案。
URLSession能够实现以下主要功能：
文件下载
文件上传
下载管理
以下是通过URLSession实现图片下载的断点续传功能的代码示例：
@interface ViewController () { NSURLSessionDownloadTask * _task; NSData * _data; NSURLSession * _session; NSURLRequest * _request; UIProgressView * _progress; UIImageView * _imageView;} _imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 300, 300)];_imageView.center = self.view.center;[self.view addSubview:_imageView];_progress = [[UIProgressView alloc] initWithFrame:CGRectMake(_imageView.frame.origin.x, _imageView.frame.origin.y + 400, 300, 40)];[self.view addSubview:_progress];// 添加三个按钮（同样的方式添加）UIButton * button = [[UIButton alloc] initWithFrame:CGRectMake(50, _imageView.frame.origin.y + 400 + 20, 50, 40)];button.backgroundColor = [UIColor blueColor];[button setTitle:@"开始" forState:UIControlStateNormal];[button addTarget:self action:@selector(ddLoad) forControlEvents:UIControlEventTouchUpInside];button.layer.borderWidth = 1;button.layer.borderColor = [UIColor blueColor].CGColor;button.layer.cornerRadius = 5;[self.view addSubview:button];
- (void)ddLoad { NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration]; _session = [NSURLSession sessionWithConfiguration:config delegate:self delegateQueue:nil]; // 注意：@src应替换为实际的图片URL NSURL *url = [NSURL URLWithString:@"https://example.com/image.png"]; _request = [NSURLRequest requestWithURL:url]; _task = [_session downloadTaskWithRequest:_request]; NSLog(@"开始下载"); [_task resume];} - (void)pause { NSLog(@"暂停下载"); [_task cancelByProducingResumeData:^(NSData *resumeData) { _data = resumeData; }]; _task = nil;}- (void)resume { NSLog(@"恢复下载"); if (!_data) { NSURL *url = [NSURL URLWithString:@"https://example.com/image.png"]; _request = [NSURLRequest requestWithURL:url]; _task = [_session downloadTaskWithRequest:_request]; } else { _task = [_session downloadTaskWithResumeData:_data]; } [_task resume];} #pragma mark delegate- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location { // 假设图片保存路径为"/Users/jredu/Desktop/tt.png" NSFileManager *manager = [NSFileManager defaultManager]; [manager moveItemAtURL:location toURL:[NSURL fileURLWithPath:@"/Users/jredu/Desktop/tt.png"] error:nil]; dispatch_async(dispatch_get_main_queue(), ^{ NSData *data = [manager contentsAtPath:@"/Users/jredu/Desktop/tt.png"]; UIImage *image = [[UIImage alloc] initWithData:data]; _imageView.image = image; UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:@"下载完成" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil]; [alert show]; });}- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite { CGFloat progress = (totalBytesWritten * 1.0) / totalBytesExpectedToWrite; dispatch_async(dispatch_get_main_queue(), ^{ _progress.progress = progress; });} 为了确保应用在不同的网络环境下都能正常运行，可以使用AFNetworkReachabilityManager进行网络状态监控：
- (void)_checkNet { [[AFNetworkReachabilityManager sharedManager] startMonitoring]; [[AFNetworkReachabilityManager sharedManager] setReachabilityStatusChangeBlock:^(AFNetworkReachabilityStatus status) { if (status == AFNetworkReachabilityStatusReachableViaWiFi) { NSLog(@"当前使用WiFi"); } else if (status == AFNetworkReachabilityStatusReachableViaWWAN) { NSLog(@"当前使用3G网络"); } else if (status == AFNetworkReachabilityStatusNotReachable) { NSLog(@"当前无网络连接"); } else { NSLog(@"网络状态未知"); } }];} URLSession在iOS应用开发中提供了更高效的网络管理功能，尤其在后台任务和断点续传方面表现优异。通过合理配置和代理方法，开发者可以实现多种网络需求，同时充分利用AFNetworking等框架的优势，提升应用的性能和用户体验。
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