MacCatalyst Multi window App not calling Scene Delegate

Question

Created Jun ’21

Replies 3

Boosts 1

Views 1.6k

Participants 3

I have a working Mac Catalyst app which opens several ViewControllers simultaneously, each in their own Scene. Once the scenes are opened and all foreground, I would like each ViewController to be notified when the user taps that window so its Scene becomes Active, i.e., topmost, first Responder and focus.

However, after the initial scene creation and activation, the Scene Delegate sceneDidBecomeActive method does not get triggered by any user interaction, despite the targeted window cycling between Active and Inactive.

Neither does UIKit post the "didBecomeActiveNotification" event.

Inside the ViewControllers, the "viewDidAppear" method does not get invoked either.

Is there a UISceneConfigurationOption required to handle an activate event?

How can I detect an Activate event on an existing scene/ViewController?

Boost

Answer 1

Frameworks Engineer OP

Apple

Jun ’21

On Mac Catalyst, windows do not become inactive when they lose key, and do not become active when they become key or frontmost. As such, you can’t use scene active/inactive callbacks to follow this state.

You might want to follow the key status of your UIWindows instead. Use UIWindow.didBecomeKeyNotification and .didResignKeyNotification to keep track of this state.

0

Answer 2

Frameworks Engineer OP

Apple

Jun ’21

You can observe the activeAppearance trait. Try this:

final class ViewController: UIViewController {
    @IBOutlet weak var statusLabel: UILabel!

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        updateWindowStatusLabel()
    }

    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        if previousTraitCollection == nil || previousTraitCollection!.activeAppearance != traitCollection.activeAppearance {
            updateWindowStatusLabel()
        }
    }

    private func updateWindowStatusLabel() {
        if traitCollection.activeAppearance == .active {
            statusLabel.text = "Appears active"
        } else {
            statusLabel.text = "Appears inactive"
        }
    }
}

2

Answer 3

Aviametrix OP

Jun ’21

I fixed the layout reversion issue by calling my method that mods the layout constraints from an override of viewDidLayoutSubbviews in each affected VC

For the moment, I am sticking with the NSWindowDidBecomeMainNotification event to trigger activation events in my viewControllers, despite the slight increase in overhead by observing the event in all open VC.

0