If you have created your widget and designer already, you can still add several views for your widget designer, which need to inherit the ContentViewDesignerView.
You can have a look at the example in our SDK - the Products module - ProductDesigner.cs. We add the views of the designer manually in the AddViews() method. By adding a new view, it will be available for styling and additional logic, for example choosing different templates.
All the best,
the Telerik team
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