通过设置代理我们可以拿到下载进度，对于大文件，我们还需要做到开始、暂停、继续以及取消等相应操作，这篇文章先简单的介绍一下通过代理来实现文件下载的问题：

#import "ViewController.h"@interface ViewController ()<NSURLSessionDownloadDelegate>@end@implementation ViewController-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{ [self delegate];}-(void)delegate{ //1.url NSURL *url = [NSURL URLWithString:@"http://120.25.226.186:32812/resources/images/minion_03.png"]; //2.创建请求对象 NSURLRequest *request = [NSURLRequest requestWithURL:url]; //3.创建session ：注意代理为NSURLSessionDownloadDelegate NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:[NSOperationQueue mainQueue]]; //4.创建Task NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithRequest:request]; //5.执行Task [downloadTask resume];}#pragma mark ----------------------#pragma mark NSURLSessionDownloadDelegate/** * 写数据 * * @param session 会话对象 * @param downloadTask 下载任务 * @param bytesWritten 本次写入的数据大小 * @param totalBytesWritten 下载的数据总大小 * @param totalBytesExpectedToWrite 文件的总大小 */-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite{ //1. 获得文件的下载进度 NSLog(@"%f",1.0 * totalBytesWritten/totalBytesExpectedToWrite);}/** * 当恢复下载的时候调用该方法 * * @param fileOffset 从什么地方下载 * @param expectedTotalBytes 文件的总大小 */-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didResumeAtOffset:(int64_t)fileOffset expectedTotalBytes:(int64_t)expectedTotalBytes{ NSLog(@"%s",__func__);}/** * 当下载完成的时候调用 * * @param location 文件的临时存储路径 */-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location{ NSLog(@"%@",location); //1 拼接文件全路径 NSString *fullPath = [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:downloadTask.response.suggestedFilename]; //2 剪切文件 [[NSFileManager defaultManager]moveItemAtURL:location toURL:[NSURL fileURLWithPath:fullPath] error:nil]; NSLog(@"%@",fullPath);}/** * 请求结束 */-(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error{ NSLog(@"didCompleteWithError");}@end

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