通过NSURLSessionDownloadTask代理实现下载大文件

//
//  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