Office PowerPoint: how to apply a new Design I created via ActivePresentation.Designs.Add()

Question

I'm trying to create a new slide master and apply it to current presentation, code below:

    var design = app.ActivePresentation.Designs.Add("my own design");
    app.ActivePresentation.Apply??

I tried ApplyTheme and ApplyTemplate, they all throw exception

System.Runtime.InteropServices.COMException (0x80048240): Presentation (unknown member) : Invalid request.  PowerPoint could not open the file.
   at Microsoft.Office.Interop.PowerPoint.PresentationClass.ApplyTheme(String themeName)

Any idea? thanks in advance.

Answer 1

Use:

ActivePresentation.Slides.Range.Design = design