@interface HMViewController ()@property (weak, nonatomic) IBOutlet UIImageView *imageView;@end@implementation HMViewController- (void)viewDidLoad{    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.}- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{    // 在子线程中调用download方法下载图片    [self performSelectorInBackground:@selector(download) withObject:nil];}/** * 下载图片 : 子线程 */- (void)download{    // 1.根据URL下载图片    NSURL *url = [NSURL URLWithString:@"http://news.baidu.com/z/resource/r/image/2014-06-22/2a1009253cf9fc7c97893a4f0fe3a7b1.jpg"];    NSLog(@"-------begin");    NSData *data = [NSData dataWithContentsOfURL:url]; // 这行会比较耗时    NSLog(@"-------end");    UIImage *image = [UIImage imageWithData:data];        // 2.回到主线程显示图片//    [self.imageView performSelector:@selector(setImage:) onThread:[NSThread mainThread] withObject:image waitUntilDone:NO];    // setImage: 1s    [self.imageView performSelectorOnMainThread:@selector(setImage:) withObject:image waitUntilDone:NO];//    [self performSelectorOnMainThread:@selector(settingImage:) withObject:image waitUntilDone:NO];}/** * 设置(显示)图片: 主线程 *///- (void)settingImage:(UIImage *)image//{//    self.imageView.image = image//}