如何判断 UIViewController 的视图是否可见

Question

I have a tabbar application, with many views. Is there a way to know if a particular UIViewController is currently visible from within the UIViewController? (looking for a property)

转载于:https://stackoverflow.com/questions/2777438/how-to-tell-if-uiviewcontrollers-view-is-visible

Answer 1

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

[EDIT] Invoking the view method causes the view to load (if it is not loaded) which is unnecessary and may be undesirable. It would be better to check first to see if it is already loaded. I've added the call to isViewLoaded to avoid this problem.

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

Or if you have a UINavigationController managing the view controllers, you could check its visibleViewController property instead.

Also, in Swift on iOS 9 (or later):

if viewController.viewIfLoaded?.window != nil {
    // viewController is visible
}