我想我陷入僵局但不太明白为什么

Question

我正在尝试使用GCD一个接一个地放置图像,如下所示

-(void)setUpImages {
    NSArray *images  =   @[[UIImage imageNamed:@"blogger-icon.png"],
                           [UIImage imageNamed:@"gplus-icon.png"],
                            [UIImage imageNamed:@"facebok-icon.png"]
                           ];
    [images enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
          dispatch_sync(dispatch_get_main_queue(), ^{
                UIImageView     *imageView  =   [[UIImageView alloc] initWithFrame:CGRectMake(80, idx * ((UIImage*)obj).size.height + idx*30 + 10, ((UIImage*)obj).size.width, ((UIImage*)obj).size.height)];
                NSLog(@"index is %@",NSStringFromCGRect(imageView.frame));

                [imageView setImage:(UIImage*)obj];
                [self.view.layer addSublayer:imageView.layer];
                sleep(1); 
            });
    }];

}

我正在使用,dispatch_sync因为我希望它会等到它的块完成(第一个图像放在屏幕上)然后第二个图像将是,所以第三个图像.现在所有的事情都发生在主线上.

但是,似乎我在中间遇到了僵局,我的逻辑在某些方面是错误的.

我需要帮助来了解这种情况.请帮忙.

Answer 1

来自以下文件dispatch_sync:

调用此函数并以当前队列为目标会导致死锁.

也就是说,我认为你有一个设计问题,你可以在不涉及GCD的情况下达到预期的效果.

由于您希望每隔k秒更新一次UI ,因此请避免使用sleep(1)延迟使用和调用方法performSelector:withObject:afterDelay:.

就像是

- (void)updateImageViewWithImageAtIndex:(NSNumber *)i {
    UIImage * image = self.images[i.intValue];
    UIImageView * imageView = [[UIImageView alloc] initWithFrame:CGRectMake(80, idx * image.size.height + idx*30 + 10, image.size.width, image.size.height)];
    NSLog(@"index is %@",NSStringFromCGRect(imageView.frame));
    [imageView setImage:image];
    [self.view.layer addSublayer:imageView.layer];

    if (i < images.count - 1) {
        [self performSelector:@selector(updateImageViewWithImageAtIndex:) withObject:@(i.intValue++) afterDelay:1];
    }
}

- (void)setUpImages {
    // Assuming you have declared images as a property
    self.images = @[[UIImage imageNamed:@"blogger-icon.png"],
                        [UIImage imageNamed:@"gplus-icon.png"],
                        [UIImage imageNamed:@"facebok-icon.png"]
                       ];
    [self updateImageViewFromImages:images index:0];
}