block下载任务

- (void)touchesBegan:(NSSet
   
     *)touches withEvent:(UIEvent *)event{    //会话    NSURLSession *session=[NSURLSession sharedSession];    //2.根据会话创建任务    NSURLSessionDownloadTask *downloadTask= [session downloadTaskWithURL:[NSURL URLWithString:IMAGE_URL] completionHandler:^(NSURL * _Nullable location, NSURLResponse * _Nullable response, NSError * _Nullable error) {        //location是下载的本地地址		NSLog(@"location=%@",location);        UIImage *image=[UIImage imageWithData:[NSData dataWithContentsOfURL:location]];        dispatch_async(dispatch_get_main_queue(), ^{            self.imagview.image=image;        });            }];    //3.启动任务    [downloadTask resume];}

下载代理方法

#import "ViewController.h"#define MYURL @"http://vjs.zencdn.net/v/oceans.mp4"@interface ViewController ()
   
    @property (nonatomic,strong)NSURLSessionDownloadTask *task;@property(nonatomic,strong) NSData *data;@property(nonatomic,strong) NSURLSession *session;@end@implementation ViewController //创建会话-(NSURLSession *)session{    if(!_session){        _session=[NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:[[NSOperationQueue alloc]init]];    }    return _session;}- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.}- (IBAction)start:(UIButton *)sender {    //根据会话创建下载任务    self.task=[self.session downloadTaskWithURL:[NSURL URLWithString:MYURL]];        //启动任务    [self.task resume];}- (IBAction)pause:(UIButton *)sender {   // [self.task suspend];//可以恢复任务    //cancelByProducingResumeData任务无法恢复，如果还是想能恢复继续下载，则记录下当前下载的数据    [self.task cancelByProducingResumeData:^(NSData * _Nullable resumeData) {        //resumeData表示当前下载了多少数据        self.data=resumeData;    }];}- (IBAction)resume:(UIButton *)sender {   // [self.task resume];   //对应cancelByProducingResumeData的在暂停的基础上继续下载    self.task=[self.session downloadTaskWithResumeData:self.data];    [self.task resume];}#pragma mark -协议方法-(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error{}//下载进度/* bytesWritten 当前次下载的数据大小 totalBytesWritten 总共下载了多少数据 totalBytesExceptedToWrite */-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite{    NSLog(@"--%f",1.0*totalBytesWritten/totalBytesExpectedToWrite);    }//恢复任务时调用的方法- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didResumeAtOffset:(int64_t)fileOffset expectedTotalBytes:(int64_t)expectedTotalBytes{    }//下载之后 文件所在位置-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location{    //location文件下载的路径}@end

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