gistfile1.cs

if (KeyboardType == UIKeyboardType.NumberPad)
			{
				NSNotificationCenter.DefaultCenter.AddObserver (  
				    "UIKeyboardDidShowNotification", (notification) => {  
						UIButton doneButton = new UIButton(new RectangleF(0, 163, 106, 53)); //{ButtonType = UIButtonType.Custom};
				
						//doneButton.SetTitle("Done", UIControlState.Normal);
						doneButton.SetImage(UIImage.FromFile("DoneUp.png"), UIControlState.Normal);
						doneButton.SetImage(UIImage.FromFile("DoneDown.png"), UIControlState.Highlighted);
						doneButton.AdjustsImageWhenHighlighted = false;
						UIWindow window = UIApplication.SharedApplication.Windows[1];
						foreach (var v in window.Subviews)
						{
						
							//NSString desc = Runtime.GetNSObject (Messaging.IntPtr_objc_msgSend (v.Handle, Selector.GetHandle ("description")));
							NSObject desc = Runtime.GetNSObject (Messaging.IntPtr_objc_msgSend (v.Handle, Selector.GetHandle ("description")));
							Console.WriteLine(desc.ToString());
							if (desc.ToString ().StartsWith ("<UIKeyboard")) {
								//v.Tag = 313377269;
								//KeyboardHandle = v.Handle;
								v.AddSubview(doneButton);
							}
						}
						doneButton.TouchUpInside += delegate {
							entry.ResignFirstResponder(); 
							
						};
				        Console.WriteLine ("Keyboard went up");  
				    }); 
				
			}