How to make CComboBox response to WM_RBUTTONDOWN message?

[Arjay]

I understand your point, somehow I got this requirement which contradict to the default behavior of the Control.
However, for all the business applications such as MS Office, Visual Studio etc, the behavior is
that, right click mouse will cancel the dropdown list of any combobox. I would appreciate if
anyone has done this before or know a custom combobox control that works this way.

The MFC CComboBox has this behavior because it's simply a wrapper to the underlying Windows control.

MS Office, Visual Studio, etc have their own custom controls (which aren't necessarily based on the OS Windows controls).

That being said, you may check out the MFC feature pack that is available on 2008 as it may emulate the new Office styled controls.

If this isn't an option, I would go back to the author of the spec/requirements and explain that getting identical Office behavior isn't trivial.