iMessage apps keeps getting restarted - ios

Question

Whenever I swipe outside of my iMessage app to open another iMessage app, and then come back to my iMessage app by swiping back, my iMessage app gets loaded again.
Even viewDidLoad of MessagesViewController gets called again.
My code in MessagesViewController looks like-
class MessagesViewController: MSMessagesAppViewController {
override func viewDidLoad() {
super.viewDidLoad()
openSuitableController()
}
override func willTransition(to presentationStyle: MSMessagesAppPresentationStyle) {
removeAllChildViewControllers()
}
override func didTransition(to presentationStyle: MSMessagesAppPresentationStyle) {
openSuitableController()
}
}
In openSuitableController, I just add a childViewController to MessagesViewController.
Because the apps start again, the collectionView gets loaded and scrolled to the top and it leads to flickering.
Please do comment if you need more info.
PS: I have added Objective-C tag because I don't feel this problem is due to specific language.

Answer 1

I believe this is unavoidable and is just the way that iMessage manages the iMessage apps that it hosts. i.e.: The iMessage framework closes your app when you swipe out and starts up the next one you swipe into. This is true with iOS 11 and prior, it might change in the future of course.
iMessage has a rather complicated way of presenting your UI by embedding it in its own sandboxed container view controller hierarchy, this is to ensure secure trust boundaries between iMessage itself and the private chat data and your application. As a result, there is more overhead in presenting your app than if your app was starting up by itself, my guess is that apps are restarted like this in order to minimise resource usage and to protect iMessage from running out of the resources it needs.
It's worth keeping your app startup as quick as possible (for example by limiting dynamic library loading time) and keep in mind how your initial content will look as it is swapped for the stored snapshot.
I believe its really important to minimise the work that is done when your app starts and when it stops in order to allow the smoothest transitions between apps.
When you swipe out of an app to another one iMessage makes a snapshot image of the previous UI state and then at the time of swiping back in to your app it displays that snapshot while your app goes through its initialisation.
So it pays to look carefully at the snapshot process and try to make sure your initial UI presentation will transition well from the snapshot that is made by the iMessage framework.