NSURLSession下载以及断点续传

NSURLSession是iOS7之后新的网络接口，和经常用到NSURLConnection是类似的。在程序在前台时，NSURLSession与NSURLConnection可以相互的替代。但是当用户在对程序进行强制关闭的时候此时NSURLSession会默认的自动断开。相比而言NSURLSession的优势主要体现在后台操作时候，而且在最流行的框架AFNetworking中也对NSURLSession提供了更好的支持。

主要提供的功能如下：

1 下载文件到内存中

2 下载文件到路径

3 上传制定的文件等

案例演示：图片下载断点续传

主要代码：

1、定义几个全局变量

@interface ViewController ()

{

    NSURLSessionDownloadTask * _task;

    NSData * _data;

    NSURLSession * _session;

    NSURLRequest * _request;

    UIProgressView * _pro;

    UIImageView * _imageView;

}

2、向视图中添加图片进度条

_imageView=[[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 300, 300)];

    _imageView.center=self.view.center;

    [self.view addSubview:_imageView];

_pro=[[UIProgressView alloc] initWithFrame:CGRectMake(_imageView.frame.origin.x, _imageView.frame.origin.y+400, 300, 40)];

3、向视图中添加按钮（同样的方式添加三个）

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];

4、通过AFNetworkReachabilityManager网络状态监测

- (void) _checkNet{

    //开启网络状态监控

    [[AFNetworkReachabilityManager sharedManager] startMonitoring];

    [[AFNetworkReachabilityManager sharedManager] setReachabilityStatusChangeBlock:^(AFNetworkReachabilityStatus status) {

        if(status==AFNetworkReachabilityStatusReachableViaWiFi){

            NSLog(@"当前是wifi");

        }

        if(status==AFNetworkReachabilityStatusReachableViaWWAN){

             NSLog(@"当前是3G");

        }

if(status==AFNetworkReachabilityStatusNotReachable){

             NSLog(@"当前是没有网络");

        }

if(status==AFNetworkReachabilityStatusUnknown){

             NSLog(@"当前是未知网络");

        }

    }];

}

5、开始下载

- (void) ddLoad{

    NSURLSessionConfiguration * config=[NSURLSessionConfiguration defaultSessionConfiguration];

    _session=[NSURLSession sessionWithConfiguration:config delegate:self delegateQueue:nil];

    //

    NSURL *url=[NSURL URLWithString:@src];

    _request=[NSURLRequest requestWithURL:url];

    _task= [_session downloadTaskWithRequest:_request];

    NSLog(@"开始加载");

    [_task resume];

}

6、设置暂停和回复

- (void) pause{

    //暂停

    NSLog(@"暂停下载");

    [_task cancelByProducingResumeData:^(NSData *resumeData) {

        _data=resumeData;

    }];

    _task=nil;

}

- (void) resume{

    //恢复

     NSLog(@"恢复下载");

    if(!_data){

        NSURL *url=[NSURL URLWithString:@src];

        _request=[NSURLRequest requestWithURL:url]；

        _task=[_session downloadTaskWithRequest:_request];

    }else{

        _task=[_session downloadTaskWithResumeData:_data];

    }

    [_task resume];

}

7、代理方法保存下载文件监控下载进度

#pragma mark - delegate

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location{

    NSURL * url=[NSURL fileURLWithPath:@"/Users/jredu/Desktop/tt.png"];

    NSFileManager * manager=[NSFileManager defaultManager];

    [manager moveItemAtURL:location toURL:url 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(), ^{

        _pro.progress=progress;

    }) ;

}