CFNotificationCenter repeating events statements - ios

Question

I have been working on an enterprise iOS/Swift (iOS 11.3, Xcode 9.3.1) app in which I want to be notified if the screen changes (goes blank or becomes active) and capture the events in a Realm databse. I am using the answer from tbaranes in detect screen unlock events in IOS Swift and it works, but I find added repeats as the screen goes blank and becomes active:
Initial Blank: a single event recorded
Initial Re-activiation: two events are recorded
Second Blank: two events are recorded
Second Re-act: three events are recorded
and this cycle of adding an additional event recording each cycle.
This must be something in the code (or missing from the code) that is causing an additive effect but I can’t find it. And, yes, the print statements show the issue is not within the Realm database, but are actual repeated statements.
My code is below. Any suggestions are appreciated.
CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(), //center
Unmanaged.passUnretained(self).toOpaque(), // observer
displayStatusChangedCallback, // callback
"com.apple.springboard.hasBlankedScreen" as CFString, // event name
nil, // object
.deliverImmediately)
}
private let displayStatusChangedCallback: CFNotificationCallback = { _, cfObserver, cfName, _, _ in
guard let lockState = cfName?.rawValue as String? else {
return
}
let catcher = Unmanaged<AppDelegate>.fromOpaque(UnsafeRawPointer(OpaquePointer(cfObserver)!)).takeUnretainedValue()
catcher.displayStatusChanged(lockState)
print("how many times?")
}
private func displayStatusChanged(_ lockState: String) {
// the "com.apple.springboard.lockcomplete" notification will always come after the "com.apple.springboard.lockstate" notification
print("Darwin notification NAME = \(lockState)")
if lockState == "com.apple.springboard.hasBlankedScreen" {
print("A single Blank Screen")
let statusString = dbSource() // Realm database
statusString.infoString = "blanked screen"
print("statusString: \(statusString)")
statusString.save()
return
}