线程4--线程间通信

子线程执行完延时操作后返回主线程，这就是通信

-(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];
}
-(void)download
{
    //1.根据URL下载图片
    //从网络中下载图片
    NSURL *urlstr=[NSURL URLWithString:@"http://cdn.duitang.com/uploads/item/201409/17/20140917231336_URiHE.jpeg"];
    NSLog(@"touch down ");
    
    //把图片转换为二进制的数据
    NSData *data=[NSData dataWithContentsOfURL:urlstr];//这一行操作会比较耗时
    
    //把数据转换成图片
    UIImage *image=[UIImage imageWithData:data];
    
    //2.回到主线程中设置图片
        //第一种方式
    //    [self performSelectorOnMainThread:@selector(settingImage:) withObject:image waitUntilDone:NO];
    
    //第二种方式
        [self.iconView performSelector:@selector(setImage:) onThread:[NSThread mainThread] withObject:image waitUntilDone:NO];
    }
//设置显示图片
-(void)settingImage:(UIImage *)image
{
    self.iconView.image=image;
}