KeyboardDismissGestureRecognizer automatically dismisses the onscreen keyboard in Xamarin.iOS when a user taps outside an editable view. Simply add a KeyboardDismissGestureRecognizer to your application's main window in FinishedLaunching.

KeyboardDismissGestureRecognizer.cs

/// <summary>
/// To automatically dismiss the onscreen keyboard in iOS when a user taps outside an editable view,
/// add a KeyboardDismissGestureRecognizer to your application's main window in FinishedLaunching, e.g.:
///     Window.AddGestureRecognizer(new KeyboardDismissGestureRecognizer());
/// </summary>
public class KeyboardDismissGestureRecognizer : UITapGestureRecognizer
{
	public KeyboardDismissGestureRecognizer() : base(() => { }) { CancelsTouchesInView = false; }

	public override void TouchesBegan(NSSet touches, UIEvent evt)
	{
		base.TouchesBegan(touches, evt);
		var touch = evt.AllTouches.AnyObject as UITouch;
		if (touch != null && touch.View != null && !(touch.View.CanBecomeFirstResponder) && View != null) View.EndEditing(true);
	}
}