How to make a .NET COM wrapper generic

Question

I think this is a factory / provider type story but I'm not sure how to describe my problem. It goes like this.

InstallShield has a COM Automation Interface that they change the name of it with each release. If it was VBScript I'd say

set project = CreateObject("ISWiAuto15.ISWiProject) ' InstallShield 2009
set project = CreateObject("ISWiAuto16.ISWiProject) ' InstallShield 2010

once I have a project object I can do things like

project.OpenProject( filePath, readOnly )

In C# .NET 3.5 I add my COM reference and do the same things except now I'm tightly coupled to that class. I want to be able to do something like

var project = CreateProjectObject( typeof ISWiAutoXX.ISWiProject )

But I can't figure out how to do this as there doesn't seem to be any shared interface to cast with.

Am I out of luck or is there a way to handle this type of a problem?

Answer 1

Thinking round the issue I think I see a possible solution done a different way but its a bit esoteric.

References are part of the the msbuild (project) file in an ItemGroup. You can externalise this by having this particular reference in another msbuild file in the project included in the proj file.

Finally you can make this external MSBUILD file T4 generated based on some logic that looks up the COM interface and determines what the reference contains.

Answer 2

If you're only using .NET 3.5, the best option would probably be to write your own interfaces that expose the exact functionality you require, and then implement the interfaces using IS 2009 and IS 2010. This allows you to use any implementation internally, and create a factory method (or use DI) to construct the objects.

Unfortunately, this does require a fair amount of simple pass through (wrapper methods that just call the COM object). However, it's a very robust, future proof way of operating, and lets you work with a simple, typesafe API.

Answer 3

If you are so inclined you could customize the run time callable wrapper so the type names are constant

Answer 4

If you're happy to give up type safety, dynamic would be helpful, but you say it's not available to you.

But you can get pretty close to dynamic in older versions of the language, by using a simple helper class to hide the noise of reflection. It doesn't do everything that the dynamic keyword can do, but it still might work for you.

Answer 5

Use VB.NET to create a strongly typed wrapper. Then you can call that wrapper from your C# application.