NSURLConnection 异步下载图片

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#pragma mark 下载歌曲
- (IBAction)downloadMP3:(UIButton *)sender {NSURL *url = [NSURL URLWithString:@"http://music.baidu.com/data/music/file?link=http://yinyueshiting.baidu.com/data2/music/239130183/12267411954000128.mp3?xcode=1a1fdb87afc200037ed60eb536e08c87&song_id=122674119"];NSURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10.0f];[NSURLConnection connectionWithRequest:request delegate:self];}
#pragma mark 获取服务器响应后调用该方法，只调用一次，获取响应对象
-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{//创建mp3Dataself.mp3Data = [[NSMutableData alloc]init];//获取MP3总大小self.mp3Length = [response expectedContentLength];
}
#pragma mark 方法是接受到数据 之后回调 调多次
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{[self.mp3Data appendData:data];self.mp3CurrentLength = self.mp3Data.length;self.progressView.progress = self.mp3CurrentLength / self.mp3Length;}
#pragma mark 整个请求完成，数据加载完成之后调用方法
-(void)connectionDidFinishLoading:(NSURLConnection *)connection{self.progressView.progress = 1;__autoreleasing NSError *error = nil;self.player = [[AVAudioPlayer alloc]initWithData:self.mp3Data error:&error];if (error) {NSLog(@"error is %@", error);} else {[self.player play];}}#pragma mark 网络连接错误时回调
-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{NSLog(@"网络连接错误 error is = %@", error);
}

    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue new] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
        if (connectionError) {
            NSLog(@"出错了");
        } else {
            //在图片视图中显示视图(应该在主线程中更新UI)
            //self.imageView.image = [UIImage imageWithData:data];
            //GCD方式在主线程中更新UI
            dispatch_async(dispatch_get_main_queue(), ^{
                self.imageView.image = [UIImage imageWithData:data];
            });
        }
       

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