Reflection In Visual Basic

Question: How does one do "reflection" in Visual Basic?

Answer: Use COM "Type Library" information.

(Assumption: We're talking about VB4 thru VB6 -- not VB7 / VB.Net, which does things entirely differently. See ReflectionInDotNet)

From the Yahoo XP discussion group:

http://groups.yahoo.com/group/extremeprogramming/message/52628

"A google groups search found a very consistent answer: No, you can't do that in VB, [...]"

Visual Basic 4..6 DLLs (and some EXEs) are COM servers. Embedded in the executable file is a COM "Type Library" containing definitions of all the public classes creatable from outside, along with their interfaces, including methods and parameters. (Every VB class is a COM interface.) Visual Studio comes with an "OLE Viewer" tool that can display type library contents in IDL (Interface Definition Language) syntax. IDL is C/C++ -like.

In theory, any Windows program can call standard COM functions to query the contents of a type library. But the functions are VB unfriendly, so you can't call them directly. There's an "unsupported" DLL in the VB6 installation that will give you access. Microsoft put out a help file that documents its use, with the usual disclaimers that they might change it on a whim. (.Net made the whole issue moot.) -- JeffGrigg

"FILE: Tlbinf32.exe : Help Files for Tlbinf32.dll (Q224331)" http://support.microsoft.com/default.aspx?scid=kb;EN-US;q224331

"Visual Basic: Inspect COM Components Using the TypeLib? Information Object Library" http://msdn.microsoft.com/msdnmag/issues/1200/TypeLib/TypeLib.asp A pretty good article on browing Type Library information from VB6. (December 2000)

I guess one could create reflection in VB, since the vbUnit guys did it. Hmmmm. Maybe I should look at the vbUnit code... -- Kay

To find it in VbUnitThree... Download http://www.maasscomputer.de/vbunit/vbUnit3.06.02.Basic.zip Look at 'vbUnit3\vbUnitFramework\Reflector.cls' -- JeffGrigg

CategoryReflection