NSURLSessionDownloadTask 下载/断点下载

实现协议NSURLSessionDownloadDelegate的2个方法
此方法主要返回文件的字节数以及已下载的字节数

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite;

储存的零时文件路径location

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

样式图，由于网速太快，手速跟不上，加载图片太快没来得及点击暂停下载以及就加载出来了，大家如果想实现可以把路径改为一个大一点的文件，这样就能看的很明显了。

代码实现

#import "ViewController.h"@interface ViewController () <NSURLSessionDownloadDelegate>@property (weak, nonatomic) IBOutlet UIImageView *loadImage;@property (weak, nonatomic) IBOutlet UIProgressView *progress;@property (weak, nonatomic) IBOutlet UILabel *loadPlan;@property (weak, nonatomic) IBOutlet UIButton *loadTitle;@property (nonatomic, strong) NSData *data;@property (nonatomic, strong) NSURLSession *session;@property (nonatomic, strong) NSURLSessionDownloadTask *task;@property (nonatomic, assign) BOOL judgeDown;@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.}- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}/** *  下载的字节 * *  @param session                   session *  @param downloadTask              taskdownload *  @param bytesWritten              每次下载的字节 *  @param totalBytesWritten         已下载的字节 *  @param totalBytesExpectedToWrite 总字节 */- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite{    //进度条计算    CGFloat progress = (totalBytesWritten*1.0)/totalBytesExpectedToWrite;    //异步添加到主队列下载    dispatch_async(dispatch_get_main_queue(), ^{        _progress.progress = progress;        _loadPlan.text = [NSString stringWithFormat:@"开始下载：%d/100",(int)(progress*100)];    }) ;}/** *  NSURLSessionDownloadDelegate委托协议 * *  @param session      session *  @param downloadTask sessiontask *  @param location     储存的零时文件路径 */- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location{    NSFileManager *manager = [NSFileManager defaultManager];    //获取document目录    NSString *strDocument = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES).lastObject;    //在原有路径上添加路径    NSString *strURL = [strDocument stringByAppendingPathComponent:@"1250538257738.jpg"];    //本地URL路径    NSURL *url = [NSURL fileURLWithPath:strURL];    if ([manager fileExistsAtPath:strURL]) {        [manager removeItemAtPath:strURL error:nil];    }    //把tem文件移动指定的URL路径上    if ([manager moveItemAtURL:location toURL:url error:nil]) {        _data = [manager contentsAtPath:strURL];        _loadImage.image = [UIImage imageWithData:_data];    }}- (IBAction)onClick:(id)sender {    NSString *strURL = @"http://img.pconline.com.cn/images/bbs4/20098/18/1250538257738.jpg";    NSURL *url = [NSURL URLWithString:strURL];    //创建config对象    NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];    //创建session对象，并添加到主队列中    _session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:[NSOperationQueue mainQueue]];    //下载路径     _task = [_session downloadTaskWithURL:url];    [_task resume];}- (IBAction)suspendLoad:(id)sender {    if (_judgeDown) {        NSLog(@"恢复下载");        _loadTitle.titleLabel.text = @"暂停下载";        if(!_data){            NSURL *url = [NSURL URLWithString:@"http://img.pconline.com.cn/images/bbs4/20098/18/1250538257738.jpg"];//            _request = [NSURLRequest requestWithURL:url];//            _task = [_session downloadTaskWithRequest:_request];            _task = [_session downloadTaskWithURL:url];        }else{            _task = [_session downloadTaskWithResumeData:_data];        }        [_task resume];    }else{        NSLog(@"暂停下载");        _loadTitle.titleLabel.text = @"恢复下载";        //取消下载并调用回调与恢复数据供以后使用        [_task cancelByProducingResumeData:^(NSData *resumeData) {            _data = resumeData;        }];        _task = nil;        _judgeDown = YES;    }}@end