AFNetworking + UIImage首先下载低分辨率图像 [英] AFNetworking+UIImage Downloading Low-Resolution Image First

问题描述

我在使用+ UIImage setImageWithURL：方法时遇到了一些麻烦。我想要做的是首先发送缩略图图像的异步请求。这个图像非常小，所以它应该很快加载。我还想发送另一个异步请求来下载图像的高分辨率版本，因为加载需要更长的时间。

I am having some troubles using the +UIImage setImageWithURL: method. What I would like to do is first send an asynchronous request for a thumbnail image. This image is very small so it should load fairly quickly. I also want to send another asynchrous request to download the hi-res version of the image since it takes a little longer to load.

我认为它会是这样的：

NSURL *thumbURL = [NSURL URLWithString:[NSString stringWithFormat:@"http://www.server.com/uploads/thumbs/%@.png", name]];
[imageView setImageWithURL:thumbURL placeholderImage:[UIImage imageNamed:@"PHImage.png"]];

NSURL *hiRezURL = [NSURL URLWithString:[NSString stringWithFormat:@"http://www.server.com/uploads/%@.png", name]];
[imageView setImageWithURL:hiRezURL];

但这只是加载高分辨率图像并且耗时太长。有什么建议吗？

but that just loads the hi-res image and takes too long. Any suggestions?

推荐答案

如果你看一下 UIImageView + AFNetworking.m的实现你看它声明了一个属性：

If you take a look at the implementation of UIImageView+AFNetworking.m you see that it declares a property:

@property (readwrite, nonatomic, retain, setter = af_setImageRequestOperation:) AFImageRequestOperation *af_imageRequestOperation;

首先是 - （void）setImageWithURL：（NSURL *） url placeholderImage：（UIImage *）placeholderImage 方法（它实际上首先调用 -setImageWithURLRequest：placeholderImage：success：failure：），是 [self cancelImageRequestOperation]; ，实际上取消了类属性的操作， af_imageRequestOperation 。

and the first thing that - (void)setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholderImage method does (it actually first calls -setImageWithURLRequest:placeholderImage:success:failure:), is [self cancelImageRequestOperation]; and that actually cancels the operation of the class property, af_imageRequestOperation.

这意味着，当您再次（在第3行）调用该方法时，它会取消第1行的操作。

That means, when you call the method again (on your 3rd) line, it cancels the operation of the 1st line.

更好的方法是如果您使用 + imageRequestOperationWithRequest：imageProcessingBlock：success：failure：并在成功块中设置图像视图的图像。我想如果你使用这种方法，你还需要在之后调用 [操作开始]; 。

A better approach would be if you use + imageRequestOperationWithRequest:imageProcessingBlock:success:failure: and set the image of image view in the success block. I think if you use this method, you need also to call [operation start]; afterwards.

希望它帮助。

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