Cannot preview mesh in c# component

I make a c# component.
In this component ,I create a mesh, and want to show this mesh.
I override DrawViewportMeshes,
but it fail to show mesh in rhino viewport.
Because this component input and output are all numbers(such as double, int),
so this component cannot has a "right click->preview"switch ,
so this I suppose, is the reason why this component cannot show mesh.

yes ,if I add a output for “Mesh”,the component can show this mesh in viewport, but my question is:if donnot add a output for “Mesh”,how to show this “preview” switch?
Thank you! @DavidRutten