What? App-B on iOS knows when I'm taking a screenshot from App-Y? I don't have iOS to check but that seems crazy.

No, I was talking about App Y knowing about a screenshot you take of App Y.

Isn’t that what everyone is talking about?

Yes, that commenter is lost.

I guess it would need permissions, but you can monitor the photo library with PHPhotoLibraryChangeObserver and check if a new item's subtype is photoScreenshot.

Otherwise userDidTakeScreenshotNotification only fires for your own app

Yes, as does android.

https://developer.apple.com/documentation/uikit/uiapplicatio...