Question

我有一个“加载”视图添加到uiimageview以指示正在加载图像，然后在调度异步我正在为图像充电并在完成后删除“加载”视图，问题是如果我调用两次这种方法，“加载”视图被添加两次，第二次从未被删除。

编辑：

在view.h上

UIView *loading;

on view.m

loading = [[UIView alloc]initWithFrame:CGRectMake(0, 0, 100, 100)];
loading.backgroundColor = [UIColor blackColor];
loading.alpha = 0.8;
loading.layer.cornerRadius = 10;
loading.center = CGPointMake(imageView.frame.size.width/2, imageView.frame.size.height/2);

if (![imageView.subviews containsObject:loading]) {
    [imageView addSubview:loading];
}
dispatch_queue_t downloadFoto = dispatch_queue_create("Get Photo", NULL);
dispatch_async(downloadFoto, ^{
    UIImage *image = [[UIImage alloc]initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:[selectedImage objectForKey:@"url"]]]];

    dispatch_sync(dispatch_get_main_queue(), ^{
        if (image) {
            [imageView setImage:image];
            [imageView setNeedsLayout];
            if ([imageView.subviews containsObject:loading]) {
                [loading removeFromSuperview];
            }
        }
    });
});

如果只调用一次，或者如果我在删除加载后调用它，一切正常，问题是如果我在块完成之前调用它。

谢谢你们，这是我最后的解决方案。

if (!blackView) {
UIActivityIndicatorView *load = [[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
blackView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, 100, 100)];
blackView.backgroundColor = [UIColor blackColor];
blackView.alpha = 0.8;
blackView.layer.cornerRadius = 10;
blackView.center = CGPointMake(fotoVisual.frame.size.width/2, fotoVisual.frame.size.height/2);
load.center = CGPointMake(blackView.frame.size.width/2, blackView.frame.size.height/2);
[load startAnimating];
[blackView addSubview:load];


[fotoVisual setImage:[UIImage imageNamed:@"previewImagen.png"]];
descripcionFotoView.text = [selectedImage objectForKey:@"titulo"];

}
if (![fotoVisual.subviews containsObject:blackView]) {
    [fotoVisual addSubview:blackView];
}
dispatch_queue_t downloadFoto = dispatch_queue_create("Get Photo", NULL);
dispatch_async(downloadFoto, ^{
    [fotoVisual setImageWithURL:[NSURL URLWithString:[selectedImage objectForKey:@"url"]]
               placeholderImage:[UIImage imageNamed:@"previewImagen.png"]];
    dispatch_async(dispatch_get_main_queue(), ^{
            [blackView removeFromSuperview];
            blackView = nil;
    });
});
dispatch_release(downloadFoto);

Answer 1

看起来你遇到的问题是你每次都在创建一个新的loading视图，这不是你想要的。每次制作新的[imageView.subviews containsObject:loading]视图时，loading永远不会成为现实。

您可以更改创建逻辑以执行此类检查

if (!loading) {
  // configure loading
  [imageView addSubview:loading];
}

然后将您的通话修改为

dispatch_sync(dispatch_get_main_queue(), ^{
  if (image) {
    [imageView setImage:image];
    [imageView setNeedsLayout];
    [loading removeFromSuperview];
    loading = nil;
  }
});

您使用dispatch_sync代替dispatch_async是否有任何特定原因？

Answer 2

在loading块

中添加dispatch_async子视图

dispatch_queue_t downloadFoto = dispatch_queue_create("Get Photo", NULL);
dispatch_async(downloadFoto, ^{

if (!loading.superview) {
// we assume your loading view doesn't have a superview so we can add it to imageView
   dispatch_sync(dispatch_get_main_queue(), ^{        
     [imageView addSubview:loading];
  };
}

    UIImage *image = [[UIImage alloc]initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:[selectedImage objectForKey:@"url"]]]];


        if (image) {
          dispatch_sync(dispatch_get_main_queue(), ^{
            [imageView setImage:image];
            [imageView setNeedsLayout];
            if ([imageView.subviews containsObject:loading]) {
                [loading removeFromSuperview];
            }
          });
        }
});

对于异步图像下载，您还可以使用SDWebimage 只需下载项目并将SDWebimage文件夹添加到您的项目中并用作下面的

#import "UIImageView+WebCache.h"

[self.imageView setImageWithURL:[NSURL URLWithString:[selectedImage objectForKey:@"url"]]
                   placeholderImage:[UIImage imageNamed:@"placeholder.png"]];

这也会缓存图像。

如何避免两次在未结束的块上添加UIView？

2 个答案: