void OnToggleShadow(object sender, EventArgs ev)
 {
     _isShadowOn = !_isShadowOn;
     ExampleBoxView.ToggleShadow(_isShadowOn);
     ButtonView.ToggleShadow(_isShadowOn);
     LabelView.ToggleShadow(_isShadowOn);
     ExampleImageview.ToggleShadow(_isShadowOn);
 }
        void OnClickedSelectionButton(object sender, EventArgs ev)
        {
            var index = Array.IndexOf(new Button[] { NoneButton, CircleButton, TriangleButton, SquareButton }, sender);
            var type  = (ViewMaskerType)index;

            if (_applyToLayout)
            {
                Stack.ApplyMask(type);
            }
            else
            {
                ExampleBoxView.ApplyMask(type);
                ButtonView.ApplyMask(type);
                LabelView.ApplyMask(type);
                ExampleImageview.ApplyMask(type);
            }
        }