URLSession数据协议下载图片

#import "ViewController.h"

@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIImageView *imageView;
@property (weak, nonatomic) IBOutlet UIProgressView *progressView;
//可变数据类型
@property (nonatomic, strong) NSMutableData *mutableData;

@end
@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    //初始化可变数据对象
    self.mutableData = [NSMutableData data];
}
- (IBAction)downloadImageByDataDelegate:(id)sender {
    //0.创建NSURL对象
    NSURL *url = [NSURL URLWithString:@"http://images.apple.com/v/iphone-5s/gallery/a/images/download/photo_1.jpg"];
    //1.session和config结合/绑定(default:默认/缺省...)
    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:config delegate:self delegateQueue:[NSOperationQueue mainQueue]];
    //2.创建数据任务
    NSURLSessionDataTask *dataTask = [session dataTaskWithURL:url];
    //3.执行任务
    [dataTask resume];
}

//delegate监听进度(周期性的触发方法)
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data {
    //data:每次服务器返回的资源的数据值
    NSLog(@"每次返回的数据大小:%lu;数据总大小:%lld", (unsigned long)data.length, dataTask.countOfBytesExpectedToReceive);
    
    //存储每次服务器返回data值
    [self.mutableData appendData:data];
    //更新imageView
    self.imageView.image = [UIImage imageWithData:self.mutableData];
    
    //更新进度
    self.progressView.progress = dataTask.countOfBytesReceived * 1.0 / dataTask.countOfBytesExpectedToReceive
    ;
}
//delegate下载完毕
- (void)URLSession:(NSURLSession *)session task:(nonnull NSURLSessionTask *)task didCompleteWithError:(nullable NSError *)error {
    
}


@end