實(shí)現(xiàn)協(xié)議NSURLSessionDownloadDelegate的2個方法
此方法主要返回文件的字節(jié)數(shù)以及已下載的字節(jié)數(shù)

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

儲存的零時文件路徑location

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

樣式圖，由于網(wǎng)速太快，手速跟不上，加載圖片太快沒來得及點(diǎn)擊暫停下載以及就加載出來了，大家如果想實(shí)現(xiàn)可以把路徑改為一個大一點(diǎn)的文件，這樣就能看的很明顯了。

屏幕快照 2016-04-14 下午1.33.37.png

屏幕快照 2016-04-14 下午1.32.49.png

代碼實(shí)現(xiàn)

#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.
}
/**
 *  下載的字節(jié)
 *
 *  @param session                   session
 *  @param downloadTask              taskdownload
 *  @param bytesWritten              每次下載的字節(jié)
 *  @param totalBytesWritten         已下載的字節(jié)
 *  @param totalBytesExpectedToWrite 總字節(jié)
 */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite{
    //進(jìn)度條計算
    CGFloat progress = (totalBytesWritten*1.0)/totalBytesExpectedToWrite;
    //異步添加到主隊列下載
    dispatch_async(dispatch_get_main_queue(), ^{
        _progress.progress = progress;
        _loadPlan.text = [NSString stringWithFormat:@"開始下載：%d/100",(int)(progress*100)];
    }) ;
}
/**
 *  NSURLSessionDownloadDelegate委托協(xié)議
 *
 *  @param session      session
 *  @param downloadTask sessiontask
 *  @param location     儲存的零時文件路徑
 */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location{
    
    NSFileManager *manager = [NSFileManager defaultManager];
    //獲取document目錄
    NSString *strDocument = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES).lastObject;
    //在原有路徑上添加路徑
    NSString *strURL = [strDocument stringByAppendingPathComponent:@"1250538257738.jpg"];
    //本地URL路徑
    NSURL *url = [NSURL fileURLWithPath:strURL];
    
    if ([manager fileExistsAtPath:strURL]) {
        [manager removeItemAtPath:strURL error:nil];
    }
    //把tem文件移動指定的URL路徑上
    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];
    //創(chuàng)建config對象
    NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
    //創(chuàng)建session對象，并添加到主隊列中
    _session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:[NSOperationQueue mainQueue]];
    //下載路徑
     _task = [_session downloadTaskWithURL:url];
    [_task resume];
}
- (IBAction)suspendLoad:(id)sender {
    if (_judgeDown) {
        NSLog(@"恢復(fù)下載");
        _loadTitle.titleLabel.text = @"暫停下載";
        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(@"暫停下載");
        _loadTitle.titleLabel.text = @"恢復(fù)下載";
        //取消下載并調(diào)用回調(diào)與恢復(fù)數(shù)據(jù)供以后使用
        [_task cancelByProducingResumeData:^(NSData *resumeData) {
            _data = resumeData;
        }];
        _task = nil;
        _judgeDown = YES;
    }
}

@end