blocks|key|4305818|text|这并不能直接回答您的问题，但解决问题的一个简单方法是在cellForRowAtIndexPath:中使用SDWebImage。他们的自述文件页面上的示例完全实现了您想要做的事情。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4305819|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/rs/SDWebImage^0|R|M|1G|A|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]]|D|@$9|Q|A|R|1|S]]|E|$]]|$1|F|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

This doesn't answer your question directly, but a simple workround to your problem would be to use <a href="https://github.com/rs/SDWebImage" rel="nofollow">SDWebImage</a> in your <code>cellForRowAtIndexPath:</code> instead. The example on their README page does exactly what you are trying to do.

blocks|key|4305905|text|当一个UITableViewCell的-layoutSubviews方法被调用时，如果它的imageView的image属性为nil，imageView就会被赋予一个(0,0,0,0)的框架。而且，-layoutSubviews只在某些情况下才会被调用:当单元格即将变得可见并且它被选中的时候。而不是在正常的滚动过程中。所以你已经看到的是，将tableView:cellForRowAtIndexPath:+sizes+cell.imageView中的占位符设置为非零大小，随后对图像所做的更改将是可见的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4305906|我通过在完成处理程序中调用[cell+setNeedsLayout]修复了这个问题，如下所示：|4305907|NSURLRequest+*request+=+[NSURLRequest+requestWithURL:[NSURL+URLWithString:MY_IMAGE_URL]];
[NSURLConnection+sendAsynchronousRequest:request
+++++++++++++++++++++++++++++++++++queue:self.operationQueue
+++++++++++++++++++++++completionHandler:%5E(NSURLResponse+*response,+NSData+*data,+NSError+*error)+{
++++++++++++++++++++++++++++++++++++++++++++[[NSOperationQueue+mainQueue]+addOperationWithBlock:%5E{
++++++++++++++++++++++++++++++++++++++++++++++++UIImage+*image+=+[UIImage+imageWithData:data];
++++++++++++++++++++++++++++++++++++++++++++++++cell.imageView.image+=+image;
++++++++++++++++++++++++++++++++++++++++++++++++[cell+setNeedsLayout];
++++++++++++++++++++++++++++++++++++++++++++}];|code-block|syntax|javascript|4305908|我发现完成块发生在后台，所以必须在主线程上执行我的UI工作。当然，这个解决方案不会考虑细胞重用等问题，但至少解决了为什么细胞的图像不会出现的问题:)|4305909|希望这能有所帮助！|4305910|entityMap^0|3|F|J|F|19|9|1J|5|1R|3|1V|9|2B|9|2R|F|4R|W|5U|E|0|D|L|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1D|8|@$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|1G|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1H|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|1I|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|1J|8|@]|D|@]|E|$]]]|R|$]]

When a <code>UITableViewCell</code>'s <code>-layoutSubviews</code> method is called, if its <code>imageView</code>'s <code>image</code> property is <code>nil</code>, <code>imageView</code> is given a frame of <code>(0,0,0,0)</code>. Also, <code>-layoutSubviews</code> only is to be called in some situations: when the cell is about to become visible and when it is selected. Not during normal scrolling. So what you've seen is that setting the placeholder inside <code>tableView:cellForRowAtIndexPath:</code> sizes <code>cell.imageView</code> to a non-zero size and subsequent changes of the image will be visible.

I fixed the issue by calling <code>[cell setNeedsLayout]</code> in the completion handler, like so:

<pre><code>NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:MY_IMAGE_URL]];
[NSURLConnection sendAsynchronousRequest:request
 queue:self.operationQueue
 completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
 [[NSOperationQueue mainQueue] addOperationWithBlock:^{
 UIImage *image = [UIImage imageWithData:data];
 cell.imageView.image = image;
 [cell setNeedsLayout];
 }];
</code></pre>

I found the completion block happens in the background so that necessitates performing my UI work on the main thread. Of course this solution won't account for cell reuse and so forth, but at least solves why the cell's image wouldn't appear :)

Hope this helps!

I am experimenting in <code>tableView:cellForRowAtIndexPath</code> to set an image by calling

<pre><code>[self downloadImage:urlString andSetIntoCellImageView:cell]
</code></pre>

and in <code>downloadImage</code>, it will call <code>NSURLConnection:sendAsynchronousRequest</code> (iOS 5 and up only), and in the completion block, set the image by using

<pre><code>cell.imageView.image = [UIImage imageWithData:data]; // data is downloaded data
</code></pre>

and it works if in <code>tableView:cellForRowAtIndexPath</code>, the <code>imageView</code> is populated with a dummy placeholder image -- and I wonder how the new image is refreshed, is it by <code>setNeedsDisplay</code> to do a repaint? But if I don't set the placeholder image, then the new image won't show at all. I wonder what mechanism can be used to make it show the image?

If I use

<pre><code>[cell.imageView setNeedsDisplay]
</code></pre>

or 

<pre><code>[cell setNeedsDisplay];
</code></pre>

in the completion block, it won't work, and if I use

<pre><code>[self.table reloadRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] 
 withRowAnimation:UITableViewRowAnimationAutomatic];
</code></pre>

in the completion block by making <code>downloadImage</code> accept the <code>indexPath</code>, it will call <code>tableView:cellForRowAtIndexPath</code> again, and cause an infinite loop. So it seems like I need to use some hash table to remember if the image is already in hash table: if not, call <code>downloadImage</code>, and if in hash table, simply use it, so there will be no infinite loop.

But is there an easy way to cause the image to show up? Setting a placeholder image works but what if we don't -- by what mechanism does placeholder cause the refresh of image?

On iOS, how to make a cell.imageView refresh its content?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我正在tableView:cellForRowAtIndexPath中进行实验，通过调用[self downloadImage:urlString andSetIntoCellImageView:cell]在downloadImage中，它将调用NSURLConnection:sendAsynchronousReque...

问在iOS上，如何让cell.imageView刷新其内容？
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问在iOS上，如何让cell.imageView刷新其内容？EN