[assembly: ExportRenderer(typeof(MyKeyboardPage), typeof(KeyboardPageRenderer))]
...
public class KeyboardPageRenderer : PageRenderer
{

    public CustomKeyboardView mKeyboardView;
    public EditText mTargetView;
    public Android.InputMethodServices.Keyboard mKeyboard;
    Activity activity;
    global::Android.Views.View view;

    protected override void OnElementChanged(ElementChangedEventArgs<Page> e)
    {
        base.OnElementChanged(e);

        if (e.OldElement != null || Element == null)
        {
            return;
        }

        try
        {
            SetupUserInterface();
            SetupEventHandlers();
            this.AddView(view);
        }
        catch (System.Exception ex)
        {
            System.Diagnostics.Debug.WriteLine(@"           ERROR: ", ex.Message);
        }
    }

    void SetupUserInterface()
    {
        activity = this.Context as Activity;
        view = activity.LayoutInflater.Inflate(Resource.Layout.activity_keyboard, this, false);

        mKeyboard = new Android.InputMethodServices.Keyboard(Context, Resource.Xml.keyboard);
        mTargetView = view.FindViewById<EditText>(Resource.Id.target);

        mKeyboardView = view.FindViewById<CustomKeyboardView>(Resource.Id.keyboard_view);
        mKeyboardView.Keyboard = mKeyboard;
    }

    void SetupEventHandlers()
    {
        mTargetView.Touch += (sender, e) =>
        {
            ShowKeyboardWithAnimation();
            e.Handled = false;
            mTargetView.ShowSoftInputOnFocus = false;
        };

        mKeyboardView.Key += async (sender, e) =>
        {
            long eventTime = JavaSystem.CurrentTimeMillis();
            KeyEvent ev = new KeyEvent(eventTime, eventTime, KeyEventActions.Down, e.PrimaryCode, 0, 0, 0, 0, KeyEventFlags.SoftKeyboard | KeyEventFlags.KeepTouchMode);

            DispatchKeyEvent(ev);

            await Task.Delay(1);

            mTargetView.RequestFocus();
        };
    }


    public void ShowKeyboardWithAnimation()
    {
        if (mKeyboardView.Visibility == ViewStates.Gone)
        {
            mKeyboardView.Visibility = ViewStates.Visible;
            Android.Views.Animations.Animation animation = AnimationUtils.LoadAnimation(
                Context,
                Resource.Animation.slide_in_bottom
            );
            mKeyboardView.ShowWithAnimation(animation);
        }
    }

    protected override void OnLayout(bool changed, int l, int t, int r, int b)
    {
        base.OnLayout(changed, l, t, r, b);

        var msw = MeasureSpec.MakeMeasureSpec(r - l, MeasureSpecMode.Exactly);
        var msh = MeasureSpec.MakeMeasureSpec(b - t, MeasureSpecMode.Exactly);

        view.Measure(msw, msh);
        view.Layout(0, 0, r - l, b - t);
    }
}