- (void)viewDidLoad{    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.}- (IBAction)downLoadImage:(id)sender {    NSString* url=@"http://pic36.nipic.com/20131203/3822951_100659752000_2.jpg";    NSThread* th=[[NSThread alloc]initWithTarget:self selector:@selector(downLoadImageFromURL:) object:url];    [th start];}-(void)downLoadImageFromURL:(NSString*)url{    NSData* data=[[NSData alloc]initWithContentsOfURL:[NSURL URLWithString:url]];    UIImage* image=[[UIImage alloc]initWithData:data];    if (image!=nil) {        [self performSelectorOnMainThread:@selector(getImage:) withObject:image waitUntilDone:YES];    }    else    {        NSLog(@"下载出错!");    }}-(void)getImage:(UIImage*)image{    self.iv.image=image;}运行之后，效果如图：