Thread: VB6: Does anyone have experience with adding moudlarity to their apps?

Well, I know that in VB.NET what you are looking for is a Interface. You would have an interface that a class from a DLL would implement. That way your original code can load the .DLL into memory and then create an instance of the class and call the implemented functions on the instanciated class.

Under VB6 the trick is "Late Binding". It all gets a bit messy and is not particularly well documented but you use CreateObject("PackageName.ObjectName") to get an instance of some registered object, then from there you need to have some standard "plugin" interface that you require from third party developers so that you can call the functions etc. E.G. you may require that all valid plugins have a name property so it might go ...

function loadplugin(byval pluginObjectName as string) as object
dim result as object
set result = nothing ' assume failure
on error goto fail
set result = createobject(pluginObjectName)
if result.Name="" then set result = nothing ' We dont allow blank plugin names
set loadplugin = result ' return object if ok.
exit function

fail:
set result = nothing ' either object not registered or didnt implement name
set loadplugin = result
end function

this function would return and instance of an object registered with the supplied classid as long as it implemented a member called name that returns a non-blank string. ActiveX controls are even messier; look into controlextender.