Capturing gyroscope data at exact moment of photo capture - ios

Question

I'm creating an app that will capture a photo and reorient it based on the gyroscope data at the time of photo capture.
I've created functions to capture the gyro data from the phone in:
startUpdates()
and to stop capturing the data in:
stopUpdates()
I tried adding this into the UIImagePickerController:
if UIImagePickerController.isSourceTypeAvailable(.camera) {
guard ptInitials.text != "" else {
missingIdentifier(text: "Please add an identifier prior to taking a photo")
return}
startUpdates()
imagePicker = UIImagePickerController()
imagePicker.delegate = self
imagePicker.allowsEditing = false
imagePicker.sourceType = UIImagePickerControllerSourceType.camera
imagePicker.cameraCaptureMode = .photo
imagePicker.modalPresentationStyle = .fullScreen
present(imagePicker,
animated: true,
completion: nil)
}
This starts the gyro capture as the image capture process begins.
I have it passing the gyro data to an optional double, livePhotoAxis: Double?, while it is measuring this inside the "startUpdates()" function.
I was attempting to get it to "stop" capturing the data once the picture is taken so the last known gyro data would be kept in my variable and able to pass into other functions;
func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
stopUpdates()
let chosenImage = info[UIImagePickerControllerOriginalImage] as! UIImage
saveImageToDocuments(image: chosenImage, fileNameWithExtension: "image.jpg")
dismiss(animated: true, completion: nil
)
}
However, the problem is that the stopUpdates() method isn't called until after the user "confirms" they like their snapped photo (vs retaking it).
From what I've read, there is a private API with uiImagePickerControllerUserDidCaptureItem that captures the exact moment the photo is taken. I could use NSNotification to try and find this and call StopUpdates() once the photo is actually taken.
Is this correct that this is a private API? Can I use that to capture this moment or will my app get rejected?
Likewise, is there a better way to turn off my gyro updates at the exact moment of photo capture?
Thanks!

Answer 1

I added this code and it fixed the problem, but I still don't know if this is a private API and will be allowed in the app store or not? Or if there is a better way to accomplish this?
NotificationCenter.default.addObserver(forName: NSNotification.Name(rawValue: "_UIImagePickerControllerUserDidCaptureItem"), object:nil, queue:nil, using: { note in
self.stopUpdates()
})
Update: This doesn't fire the EXACT moment of photo capture. It fires when the photo is "locked in". There are a few seconds (2ish) between the time the take photo button is pressed and the photo locks into place. As a result, if you move the phone during that time, the gyro data will be inaccurate.
Any thoughts on how to improve on this?