我如何知道哪个ViewController是活动的？ [英] How can I know which ViewController is active?

问题描述

我使用NSOperationQueue下载图片。

我要调用我的视图控制器的一个方法 reloadView 图像下载完成。

但是，当下载正在进行时，很可能用户已移动到其他视图。此另一个视图还将具有 reloadView 方法（例如，第一个视图显示已下载的图片总数，第二个显示下载图片的缩略图）

基本上我想要的是，每当图像下载完成，我应该能够调用活动视图控制器的 reloadView 方法？ / p>

这怎么可能？

解决方案

这种方法。这是 NSNotificationCenter 的设计用途。当您的图片完成下载后，请张贴通知。在视图需要知道它的控制器中，监听 viewDidAppear：中的通知并停止在 viewDidDisappear：中监听。您的下载代码不需要知道您的视图控制器的详细信息或其状态。

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?

解决方案

I wouldn't take that approach. This is the kind of thing NSNotificationCenter is designed for. When your image has finished downloading, post a notification. In view controllers that need to know about it, listen for the notification in viewDidAppear: and stop listening in viewDidDisappear:. Your downloading code doesn't need to know the details of your view controllers or their status.

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