iOS Question detect pressed Power OFF button

Sub Process_Globals
   Public App As Application
   Public NavControl As NavigationController
   Private Page1 As Page
   Private locked As Boolean
End Sub

Private Sub Application_Start (Nav As NavigationController)
   NavControl = Nav
   Page1.Initialize("Page1")
   Page1.Title = "Page 1"
   Page1.RootPanel.Color = Colors.White
   Page1.RootPanel.LoadLayout("input")
   NavControl.ShowPage(Page1)
   
   Dim no As NativeObject = Me
   no.RunMethod("addListener", Null)
End Sub

Sub Application_Foreground
   locked = False
End Sub

Private Sub Application_Background
   Log($"locked: ${locked}"$)
End Sub

#if objc

static void displayStatusChanged(CFNotificationCenterRef center,
  void *observer,
  CFStringRef name,
  const void *object,
  CFDictionaryRef userInfo) {
  if (name == CFSTR("com.apple.springboard.lockcomplete")) {
     [b4i_main new]._locked = true;
  }
}
- (void)addListener {
    // Override point for customization after application launch.
  CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(),
  NULL,
  displayStatusChanged,
  CFSTR("com.apple.springboard.lockcomplete"),
  NULL,
  CFNotificationSuspensionBehaviorDeliverImmediately);
}

#end if