iOS线程间通信 -NSOperation 篇

线程间实现通信，NSOperation的代码：

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    [self downLoadImageAndShow];
}
- (void)downLoadImageAndShow{

    // 获取图片属性
    __block UIImage * image1 = [[UIImage alloc] init];
    __block UIImage * image2 = [[UIImage alloc] init];
    //1. 创建 非主队列
    NSOperationQueue * queue = [[NSOperationQueue alloc] init];
   
    //2. 创建 任务 下载图片1；
    NSBlockOperation * op1 = [NSBlockOperation blockOperationWithBlock:^{
        NSString * urlStr = [NSString stringWithFormat:@"https://zuoye2.xinkaoyun.com/awm/35/iOS_09060620200720110101.jpeg"];
        NSURL * url = [NSURL URLWithString:urlStr];
        NSData * data = [NSData dataWithContentsOfURL:url];
        image1 = [UIImage imageWithData:data];
    }];
   
    //3. 创建 任务 下载图片2；
    NSBlockOperation * op2 = [NSBlockOperation blockOperationWithBlock:^{
        NSString * urlStr = [NSString stringWithFormat:@"https://zuoye2.xinkaoyun.com/awm/35/iOS_08160320200720104454.jpeg"];
        NSURL * url = [NSURL URLWithString:urlStr];
        NSData * data = [NSData dataWithContentsOfURL:url];
        image2 = [UIImage imageWithData:data];
    }];

    //4.合成图片
    NSBlockOperation * op3 = [NSBlockOperation blockOperationWithBlock:^{
        //开启图形上下文 并设置上下文宽高
        UIGraphicsBeginImageContext(CGSizeMake(200, 200));
       
        //图片画图
        [image1 drawInRect:CGRectMake(0, 0, 100, 100)];
        image1 = nil;
       
       
        [image2 drawInRect:CGRectMake(0, 100, 100, 100)];
        image2 = nil;
       
        //根据图片上下文获取图片
        UIImage * image = UIGraphicsGetImageFromCurrentImageContext();
        //关闭上下文
        UIGraphicsEndImageContext();
        //回到主线程 刷新UI
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            self.iconImageView.image = image;
        }];
    }];
   
    //添加依赖，由于异步执行，先后顺序不可控
    [op3 addDependency:op2];
    [op2 addDependency:op1];
   
    //将任务添加到队列
    [queue addOperation:op1];
    [queue addOperation:op2];
    [queue addOperation:op3];
   
}

运行结果：