图片下载

 @property (nonatomic,strong) UIButton *btnOne;
    __block typeof (_btnOne) one = _btnOne;
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSURL *url = [NSURL URLWithString:@"http://easyread.ph.126.net/G8GtEi-zmPQzvS5w7ScxmQ==/7806606224489671909.jpg"];
        NSData *data = [NSData dataWithContentsOfURL:url];
        if (data != nil) {
            dispatch_async(dispatch_get_main_queue(), ^{
                UIImage *image = [UIImage imageWithData:data];
                [one setBackgroundImage:image forState:UIControlStateNormal];
            });
        }
    });