如何检查特定的UIViewController视图当前是否可见？ [英] How to check if a specific UIViewController's view is currently visible?

问题描述

可能重复：

如何判断UIViewController的视图是否可见

我正在开发一个应用程序来处理来自网络的持续传入数据流，并为用户提供了许多不同的UIView来查看该数据。

I'm developing an app that processes a constant stream of incoming data from the network and provides a number of different UIViews for the user to view that data.

当基于来自网络的传入流更新某些模型数据时，我访问关联的UIViewController或UITableViewController并在其上执行-setNeedsDisplay（在UIViewController的情况下）或-reloadData（在UITableViewController的情况下）。

When certain model data gets updated based on the incoming stream from the network, I access the associated UIViewController or UITableViewController and do -setNeedsDisplay on it (in the case of UIViewController) or -reloadData (in the case of UITableViewController).

有没有办法检查当前是否正在显示给定的UIView（除了刚被加载），这样我只做--setNeedsDisplay或-reloadData如果用户当前正在查看UIView的？看起来在用户当前没有看到的视图上调用-setNeedsDisplay或reloadData会浪费处理能力，并且不利于电池寿命。当用户最终切换到之前已更新的视图时，在-viewWillAppear上执行-setNeedsDisplay或reloadData会更有意义。

Is there a way to check if a given UIView is currently being displayed (beyond just being loaded) so that I only do -setNeedsDisplay or -reloadData if the user is currently looking at that UIView? It would seem that calling -setNeedsDisplay or reloadData on a view that the user is not currently looking at is a waste of processing power and wouldn't be good for battery life. When the user eventually switches over to a view that previously got updated, doing -setNeedsDisplay or reloadData on the -viewWillAppear would make more sense.

谢谢

推荐答案

在做了一些研究之后，我在这里发布的另一个问题中找到了这个答案......这似乎是最好的方式...

After doing some research, I found this answer in a different question posted on here...This seems to be the best way...

如果视图当前可见，则视图的窗口属性为非零，因此请检查视图控制器中的主视图：

The view's window property is non-nil if a view is currently visible, so check the main view in the view controller:

if (viewController.isViewLoaded && viewController.view.window){
    // viewController is visible
}

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