Working with materials..

Hi,

at the moment I'm working on a material dialog. So i have a variable:
Graphic3d_MaterialAspect m_Material;
Setting the values via MFC works fine.
But the problem is I see no differences in my preview window. Heres the code:

void Im_OCCMaterialDlg::UpdatePreview()
{
SetMaterialValues();
m_PreviewShape.GetPreviewShape()->Attributes()->ShadingAspect()->SetMaterial(m_Material);
m_OCCWnd.GetAISContext()->Redisplay(m_PreviewShape.GetPreviewShape());
}

Where's my error?

Best regards,
Patrik Müller