通过NSURLSessionDownloadTask代理实现下载大文件

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////  ViewController.m//  NSURLSessionDownloadTask////  Created by hq on 16/4/17.//  Copyright © 2016年 hanqing. All rights reserved.//#import "ViewController.h"@interface ViewController () <NSURLSessionDownloadDelegate>@property (weak, nonatomic) IBOutlet UIButton *startBut;@property (weak, nonatomic) IBOutlet UIProgressView *pro;- (IBAction)startDownload:(UIButton *)sender;@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];}- (IBAction)startDownload:(UIButton *)sender {            NSURLSession *session=[NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:[[NSOperationQueue alloc]init]];            NSString *urlString=@"http://120.25.226.186:32812/resources/videos/minion_01.mp4";        NSURLSessionDownloadTask *task=[session downloadTaskWithURL:[NSURL URLWithString:urlString]];        //恢复下载任务    [task resume];        self.startBut.enabled=NO;    }-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite{        NSLog(@"已下载%lld",totalBytesWritten);        NSLog(@"文件总大小%lld",totalBytesExpectedToWrite);        //self.pro.progress=(1.0*totalBytesWritten/totalBytesExpectedToWrite);        [[NSOperationQueue mainQueue] addOperationWithBlock:^{                //必须放在主线程当中才回更新进度条－－－－－－－－－－－－－－－－－－－－－－－－－－－－－        self.pro.progress=(1.0*totalBytesWritten/totalBytesExpectedToWrite);    }];}-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location{        //NSLog(@"%@",location);        //下载完成，将文件剪切到我们的cache文件夹当中去    NSString *cachePath=NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES).firstObject;        NSString *fileName=[cachePath stringByAppendingPathComponent:@"video.mp4"];        NSFileManager *fileManager=[NSFileManager defaultManager];        [fileManager moveItemAtURL:location toURL:[NSURL fileURLWithPath:fileName] error:nil];        NSLog(@"%@",fileName);    }//不管下载成功还是失败，都会来到该方法，不过下载失败的话，error有值，下载成功error为null-(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error{        if (error) {                NSLog(@"下载失败了%@",error);    }}- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}@end
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