When using AVFoundation, how to listen for Control Center Screen and Notification Center Screen activity

Question

I use AVFoundation for a video recording. When the app goes to the background I stop the capture session and when it enters the foreground I restart the capture session, everything works fine. I also use callKit to listen for incoming phone calls and that works fine too:

NotificationCenter.default.addObserver(self, selector: #selector(appWillEnterBackground), name: UIApplication.willResignActiveNotification, object: nil)
        
NotificationCenter.default.addObserver(self, selector: #selector(appWillEnterForeground), name: UIApplication.willEnterForegroundNotification, object: nil)

@objc func appWillEnterBackground() {

    // if recording stop recording, stop timer, etc ...
    captureSession.stopRunning()
    previewLayer = nil
}

@objc func appWillEnterForeground() {

   if !captureSession.isRunning {
        captureSession.startRunning()
        initialize preview layer
   }
}

The problem is while the vc with the camera is active (recording or not) and when I swipe from the bottom to bring up the Control Center Screen or swipe from the top to bring down the Notification Center Screen UIApplication.willResignActiveNotification gets called and the capture session is stopped. When I remove either of those screens UIApplication.willEnterForegroundNotification doesn't get called and the capture session is no longer running.

What I want to do is when either of those screens surface I simply use a bool to prevent the capture session from stopping

var haveControlScreensSurfaced = false // toggle this true/false depending when the control screens enter and leave

 @objc func appWillEnterBackground() {

    if view.window != nil && haveControlScreensSurfaced { return }

    // if recording stop recording, stop timer, etc ...
    captureSession.stopRunning()
    previewLayer = nil
}

How can specifically listen for Control Center Screen and Notification Center Screen activity so that I can toggle my haveControlScreensSurfaced bool value to true/false?

Lance Samaria · Accepted Answer · 2020-07-06T01:36:24.843

This way works good for an avplayer

Since I needed a capture session long story short I used this. When sliding up/down either the Notification Center Screen or the Control Screen, UIApplication.didEnterBackgroundNotification (app enters background) and UIApplication.willEnterForegroundNotification (app is about to enter foreground) never get called. I simply moved my code to there and problem solved:

NotificationCenter.default.addObserver(self, selector: #selector(didEnterBackground), name: UIApplication.didEnterBackgroundNotification, object: nil)
        
NotificationCenter.default.addObserver(self, selector: #selector(appWillEnterForeground), name: UIApplication.willEnterForegroundNotification, object: nil)

@objc func didEnterBackground() {

    // stop capture session
}

@objc func appWillEnterForeground() {

   // start capture session
}

Here is a breakdown of what happens when the notifications are triggered:

Pressing the Home Button, sending app to the background:

1- `UIApplication.willResignActiveNotification` gets called first
2- `UIApplication.didEnterBackgroundNotification` gets called second // *** gets called when the HomeButton is pressed ***

Opening the app back up:

1- `UIApplication.willEnterForegroundNotification` gets called first  // *** gets called when the opening the app back up ***
2- `UIApplication.didBecomeActiveNotification` gets called second

Sliding down the Notification Center Screen from the top:

1- `UIApplication.willResignActiveNotification` gets called first
2- `UIApplication.didBecomeActiveNotification` gets called second
3- if using the `.AVCaptureSessionWasInterrupted` the `.videoDeviceNotAvailableInBackground` gets called third
4- `UIApplication.willResignActiveNotification` gets called fourth

Sliding the Notification Center Screen back up:

1- `UIApplication.didBecomeActiveNotification` gets called alone
2- if using the `.AVCaptureSessionInterruptionEnded` it gets called second

Sliding the Control Screen up from the bottom:

1- `UIApplication.willResignActiveNotification` gets called alone

Sliding the Control Screen back back down:

1- `UIApplication.didBecomeActiveNotification` gets called by alone

When using AVFoundation, how to listen for Control Center Screen and Notification Center Screen activity

1 Answers1