设计异步下载程序显示图像
我有一个 JSON feed，其中包含图像的 URL。我正在使用 NSURLConnection 下载 JSON feed 并提取 URL。我想异步下载所有图像。我对 UIImage 进行了子类化，并向该类发送了一个 URL，它以异步方式一次下载一张图像。
首先，这是一个好方法吗？其次，我想一次显示四张图像。难道我不应该把每组四个一起下载，而不是一个一个地下载吗？
我的第二个问题是我有两个NSURLConnection。这可能很糟糕。我是否应该使用相同的 NSURLConnection 来下载 JSON feed 并同时获取图像？
我试图一次显示四个图像，并使用下一个按钮在下一行显示接下来的四个图像。
I have a JSON feed which contains URLs for images. I am using NSURLConnection to download the JSON feed extract the URLs. I want to download all the images asynchronously. I subclassed UIImage and sent that class a URL which it downloads, one image at at a time, in an asynchronous manner.
First, is that a good way to do it? Second, I'd like to show four images at a time. Shouldn't I download every set of four together instead of downloading one by one?
My second concern is that I have twoNSURLConnections. That's probably bad. Should I use the very same NSURLConnection to download the JSON feed and at the same time get the image?
I am trying to display four images at a time, with a next button that displays the next four on the next line.
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我不确定 UIImage 是否应该被子类化。如果您需要良好的设计实践，您应该看看 TopPaid
来自 Apple 的示例代码，它展示了如何正确下载 feed，然后异步下载图像。仔细查看该项目中的
IconDownloader类，它是一个处理图像下载的类，并在完成时通知其委托。据我所知，一次拥有多个 NSURLConnection 没有问题。如果连接数量变得非常，您可能会遇到麻烦，因为这可能会使 iPhone 上允许的打开文件描述符数量饱和，或者更可能会产生内存警告。就您的情况而言，如果您只有 2 个连接，则不会有任何问题。
I am not sure UIImage is expected to be subclassed. If you need good design practice, you should have a look at TopPaid
sample code from Apple, as it is showing how to properly download a feed and then asynchronously download images. Take a close look at the
IconDownloaderclass from this project, which is a class handling image downloading, and notifying its delegate when it's finished.As far as I know there is no problem with having multiple NSURLConnections at a time. You might run into trouble if the number of connections becomes very large, because this could saturate the number of open file descriptors allowed on iPhone, or more likely create a memory warning. In your case if you only have 2 connections, you don't have any problem.