Why cannot get SelectionSet in DrawingSheet

[1354448288]

I used the following codes to get a SelectionSet from a drawing sheet, but I cannot get anything.  The Visual Studio send tips:  cannot make the System._ComObject to Inventor.SelectionSet.

Here are my code:

SelectSet selectSet = null;
            if (drawingDocument.SelectSet.Count == 0)
            {
                Console.WriteLine("Select a drawing view");
                //selectSet = inventorApp.CommandManager.Pick(SelectionFilterEnum.kDrawingViewFilter, "Select a drawing view");
                selectSet = inventorApp.CommandManager.Pick(SelectionFilterEnum.kDrawingSheetFilter, "Select drawing sheet!");
            }
            else
            {
                selectSet = drawingDocument.SelectSet;
            }

After running the codes, I choosed the red line, (of course, the other lines are banned to choose), and the Visual Studio send the message : cannot make the System._ComObject to Inventor.SelectionSet.

I am very confused about it. How should I get the SelectionSet?

[bradeneuropeArthur]

This will work:

Public Sub main()

Dim a As Object
Set a = ThisApplication.CommandManager.Pick(SelectionFilterEnum.kDrawingSheetFilter, "Select drawing sheet!")


MsgBox a.Name
End Sub

[bradeneuropeArthur · Accepted solution]

and this works too:

Public Sub main()

Dim a As SelectSet
Set a = ThisApplication.ActiveDocument.SelectSet
 a.Select(ThisApplication.CommandManager.Pick(SelectionFilterEnum.kDrawingSheetFilter, "Select drawing sheet!"))


MsgBox a.Item(1).Name
End Sub