protected virtual void RegisterForKeyboardNotifications()
{
if (_keyboardShowObserver == null)
_keyboardShowObserver = NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillShowNotification,
OnKeyboardNotification);
if (_keyboardHideObserver == null)
_keyboardHideObserver = NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillHideNotification,
OnKeyboardNotification);
}