Question

For example, if a view of a viewController is in viewHierarchy and I just finished downloading stuff, I want to update stuff quickly. If self.view is not in viewHierarchy, I want to postpone updating.

I suppose, I can just add a boolean variable to indicate that and put it on viewWillAppear and viewWillDisappear.

I can also scan windows and see if UIView is in the viewHierarchy or not.

Is there a more straightforward way?

Answer 1

As of iOS 9.0, in Swift, you can do this in your view controller:

if viewIfLoaded?.window != nil {
    // view should be updated
}

or this if you want to actually use the view:

if let view = viewIfLoaded, view.window != nil {
    // update view
}

For older versions of iOS, in Objective-C:

if (self.isViewLoaded && self.view.window != nil) {
    // view is in a view hierarchy and should be updated
}