问题描述
我在桌面视图单元格中下载图像，因为它们滚动到屏幕上。出于UX原因，我开始在 - （UITableViewCell *）tableView中下载图像：（UITableView *）tableView cellForRowAtIndexPath：（NSIndexPath *）indexPath 。我不要等到表视图完成滚动。设置表格视图单元格后，我开始下载我还没有的图像。但是，在表视图停止移动之前，它们似乎没有完全下载。一旦它停止移动，图像几乎立即下载。
I am downloading images in table view cells as they scroll onto the screen. For UX reasons, I start downloading the images in - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath. I do not wait until the table view is done scrolling. When the table view cell is set, I start downloading images that I do not have already. However, they do not seem to fully download until the table view stops moving. As soon as it stops moving, the images almost download instantly.
无论如何使用NSURLConnection，它没有被主UI线程阻止？或者，有一种方法可以在滚动表格视图时非常快速地下载这些图像。
Is there anyway to use NSURLConnection where it is not blocked by the main UI thread? Or, is there a way where these images will download very quickly while the table view is being scrolled.
**编辑**
为了证明NSURLConnection较慢，我使用NSThread在另一个线程中分离新的选择器。然后我下载数据并回调主线程，在那里我创建一个UIImage并在表视图中显示它。这个方法工作得更快。
To prove that NSURLConnection is slower I used NSThread to detach a new selector in a different thread. I then download the data and call back to the main thread where I create a UIImage and show it in the table view. This method works MUCH faster.
就我个人而言，我认为NSURLConnection被抛入事件循环，UITableView滚动阻止了它。
Personally, I think that NSURLConnection is getting thrown into the event loop where the UITableView scrolling is blocking it.
推荐答案
阅读一个很好的解释为什么所有下载委托通知都排队，但在使用主线程更改时滚动下载：
Read NSDefaultRunLoopMode vs NSRunLoopCommonModes for a good explanation of why all the download delegate notifications are queued up, but to download while scrolling when using the main thread change from this:
NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request
delegate:self];
到此：
NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request
delegate:self
startImmediately:NO];
[connection scheduleInRunLoop:[NSRunLoop currentRunLoop]
forMode:NSRunLoopCommonModes];
[connection start];
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