如何检查当前是否正在显示UIViewController？ [英] How do I check if an UIViewController is currently being displayed?

问题描述

如何检查当前是否显示 UIViewController ？

How do I check if an UIViewController is currently being displayed?

我的 UIViewControllers 正在侦听 NSNotifications - 即使它们未显示（即未显示）。所以我可以在后台观察来自 NSNotificationCenter NSNotifications 10 UIViewController C>。当 UIViewController 发布并收到 NSNotification 时，我想知道它是否正在显示。如果不是，我将设置一个布尔值，以便在显示视图时处理它。如果它当前正在显示，我会做更多的事情，比如立即更新表等等......

My UIViewControllers are listening for NSNotifications - even if when they are not displayed (ie not shown). So I could have 10 UIViewController in the background observing NSNotifications from NSNotificationCenter. When an NSNotification is posted and received by the UIViewController, I'd like to find out if it is currently being shown. If it is not, I will just set a boolean so that it will processed when the View is presented. If it currently being display, I will do more things like update tables immediately, and so forth...

推荐答案

你需要检查你的viewcontroller是否在navigationcontroller的viewcontroller数组的堆栈之上。示例代码是，

You need to check if your viewcontroller is on top of the stack of navigationcontroller's viewcontroller array. A sample code is,

if (self.navigationController.topViewController == self) {
    //the view is currently displayed
}

您可以在 viewWillAppear 检查当前视图是否可见的方法。

You can use this inside the viewWillAppear method to check whether the current view is visible.

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