Tab key not listening for CustomViewRenderer in Xamarin forms iOS

I have a xamarin forms grid and a written custom renderer for that grid in xamarin forms iOS platform. And applied BecomeFirstResposnder to that CustomRenderer on OnElementPropertyChanged. Added UIKeyCommand "\t " to the UIViewController. UpArrow,DownArrow, LeftArrow every key is listening except Tab and Shift+Tab Key. Kindly, please help me.

//CustomRenderer for Xamarin Forms Grid

protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
{
  base.OnElementPropertyChanged(sender, e);
  this.BecomeFirstResponder();
   if (this.KeyPageRenderer == null)
   {
     this.KeyPageRenderer = this.GetSfPageRenderer(this.GetControl());
     if (this.KeyPageRenderer != null)
     {  
      UIKeyCommand KeyTab = UIKeyCommand.Create(new NSString("\t"), 0, new ObjCRuntime.Selector("KeyRecV:"));
      this.KeyPageRenderer.AddKeyCommand(KeyTab);
     }
   }
}

internal UIViewController GetSfPageRenderer(UIView view)
{
  if (view != null)
  {
   var responder = (UIResponder)view;
   while (responder != null && !(responder is UIViewController))
   { 
    responder = responder.NextResponder;
   }
   return responder as UIViewController;
  }
  return null;
}

public override bool CanBecomeFirstResponder
{
 get
 {
  return true;
 }
}
[Export("KeyRecV:")]
private void Excute(UIKeyCommand keyCommand)
{
 if ((keyCommand.Input as NSObject).Description == "\t")
 {

 }
}