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I'm trying to work out the best way to update a view when the app comes into the foreground. Originally I had assumed that viewWillAppear would do the trick, but it appears I was incorrect.

I understand from other posts the correct way to do this is with the Notification Center:

NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground), name: UIApplication.willEnterForegroundNotification, object: nil)`

So far so good; this allows me to work out when this happens correctly. However it's possible I may have several views in a stack and I don't want lots of updates happening unless the view is actually visible.

I thought the following code would allow me to do this:

@objc func willEnterForeground() {
    if(self.isBeingPresented) {
        updateView()
    }
}

But unfortunately isBeingPresented is always false when the view is restoring from the background.

Does anybody have any suggestions on the best way to tell if the current view is the 'top' view in the stack?

Ben
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  • because your view-controller probably was [_pushed_](https://developer.apple.com/documentation/uikit/uinavigationcontroller/1621887-pushviewcontroller) into the navigation stack and not [_presented_](https://developer.apple.com/documentation/uikit/uiviewcontroller/1621380-present) modally – e.g. the [top view-controller](https://developer.apple.com/documentation/uikit/uinavigationcontroller/1621849-topviewcontroller) in a nav-controller, and a [selected view-controller](https://developer.apple.com/documentation/uikit/uitabbarcontroller/1621172-selectedviewcontroller) in a tab-bar controller. – holex Apr 11 '19 at 13:35
  • `isBeingPresented` is only valid in one of the `view[Will|Did][Disa|A]ppear` methods. – rmaddy Apr 11 '19 at 16:14
  • *"I don't want lots of updates happening unless the view is actually visible"* - what is the problem updating views that aren't visible? Are these expensive updates in some way? – rmaddy Apr 11 '19 at 16:15
  • @maddy potentially - I would like to update the data in a view via an API when the app enters the foreground. I'd rather only do this for a single view for this. – Ben Apr 12 '19 at 13:21

0 Answers0