Xamarin iOS: Handle keyboard with UIScrollView

KeyboardHelper.cs

public class KeyboardHelper
{
    private UIViewController _viewController;
    private UIScrollView _scrollView;

    public KeyboardHelper(UIViewController viewController)
    {
        this._viewController = viewController;
    }

    public KeyboardHelper(UIViewController viewController, UIScrollView scrollView)
    {
        this._viewController = viewController;
        this._scrollView = scrollView;

        NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.DidShowNotification, (notif) =>
        {
            this.OnKeyboardDidShow(notif);
        });

        NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillHideNotification, (notif) =>
        {
            this.OnKeyboardWillHide(notif);
        });
    }

    public void DismissKeyBoardWhenTapOutsideResponder()
    {
        var tapGesture = new UITapGestureRecognizer((obj) =>
        {
            this.DismissKeyboard();
        });

        this._viewController.View.AddGestureRecognizer(tapGesture);

        if (this._scrollView != null)
        {
            this._scrollView.KeyboardDismissMode = UIScrollViewKeyboardDismissMode.OnDrag;    
        }
    }

    public void DismissKeyboard()
    {
        this._viewController.View.EndEditing(true);
    }

    private void OnKeyboardDidShow(NSNotification notification)
    {
        var keyboardFrame = ((NSValue)notification.UserInfo[UIKeyboard.FrameEndUserInfoKey]).CGRectValue;

        this._scrollView.ContentInset = new UIEdgeInsets(new nfloat(0), new nfloat(0), keyboardFrame.Height + 20, new nfloat(0.0));
    }

    private void OnKeyboardWillHide(NSNotification notification)
    {
        this._scrollView.ContentInset = UIEdgeInsets.Zero;
    }
}