我如何知道哪个 ViewController 处于活动状态？
我正在使用 NSOperationQueue 下载图像。
我想在图像下载完成后调用视图控制器的方法reloadView。
但是，当下载正在进行时，用户很可能已移至不同的视图。这个另一个视图还将有一个 reloadView 方法（例如，第一个视图显示下载图像总数，第二个视图显示下载图像的缩略图）
基本上我想要的是，每当图像下载完成时，我应该能够调用活动视图控制器的 reloadView 方法吗？
这怎么可能？
I am downloading images using NSOperationQueue.
I want to call a method reloadView of my view controller once the image download is complete.
However when the download is in progress, it is fairly possible that user has moved to a different view. This other view will also have a reloadView method (e.g. first view shows total downloaded images count, and second shows thumbnails of download images)
Basically what I want is that whenever an image download is completed, I should be able to call the reloadView method of the active view controller whichever it is?
How can this be possible?
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我不会采取这种方法。这就是
NSNotificationCenter的设计目的。图片下载完成后，发布通知。在需要了解它的视图控制器中，在viewDidAppear:中监听通知并在viewDidDisappear:中停止监听。您的下载代码不需要知道视图控制器的详细信息或其状态。I wouldn't take that approach. This is the kind of thing
NSNotificationCenteris designed for. When your image has finished downloading, post a notification. In view controllers that need to know about it, listen for the notification inviewDidAppear:and stop listening inviewDidDisappear:. Your downloading code doesn't need to know the details of your view controllers or their status.