private void Button_OnChecked(object sender, RoutedEventArgs e)
        {
            TerrainViewModel item = ((ToggleButton)sender).DataContext as TerrainViewModel;
            Selected = item;

            ToggleButton selectedTool = sender as ToggleButton;
            if (_prevSelected != null)
                _prevSelected.IsChecked = false;
            _prevSelected = selectedTool;
        }