Me: I live in Silicon Valley with my wife, child and cat. I have worked at Microsoft since I graduated from College, both in the Macintosh Business Unit on products such as Outlook Express, Entourage, IE, and Virtual PC and in Windows Live on Hotmail, Calendar and People. I am currently a Principal Lead Program Manager on the Windows Live Social Networking team. I basically manage a team of Program Managers responsible for delivering features to support our web and client applications. I've been blogging since 2001 and like to play around with .NET in my spare time working on projects such as dasBlog (the blog that powers this site) and Send to SmugMug (an application for uploading photos to SmugMug). I blog about a number of technology and productivity related topics.
Powered by: newtelligence dasBlog 2.3.9074.18820
Disclaimer The posts on this weblog are provided "AS IS" with no warranties, and confer no rights. The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.
© Copyright 2010, Omar Shahine
E-mail
Summary
In this weeks’ installment of I hate COM, lets talk about a frustrating problem I’ve been having (turns out I had this problem when I wrote my Media Center Front Panel Display but found a different workaround I mention below). It would be nice if there were a KB article on this topic, but there isn’t and I don’t know why.
Say you are exposing a .NET component as a COM component. Not to uncommon. I already do this in my Outlook2OneNote add-in as well as my Media Center Front Panel Display. In both these cases I am implementing a COM Interface: Extensibility.IDTExtensibility2 for Outlook2OneNote and EHLib.IMediaStatusSink for my Media Center Sink.
In Outlook2OneNote the project structure looks like
In MediaCenterSink the project structure looks like
In both cases the MSI does not register the Primary Output for COM Interop. It’s not obvious why this fails, but I spent many hours trying various things (you know how trial and error is when you don’t have an understanding for what is going on or what is broken right?). So you can imagine how frustrating this is. Even more frustrating is when this happens to you twice in the course of a few months.
Approach 1: Custom Action
Well, google had no answers for me except a bunch of other people who were saying “COM Registration during install using MSI is broken…” or “vsdraCOM doesn’t do anything…” etc. The only solution that I found was to write some code in the Primary Output project like so (you need a similar Uninstall and Rollback override as well):
public override void Install(System.Collections.IDictionary stateSaver){ base.Install(stateSaver); try { RegistrationServices regSrv; // Register the assembly regSrv = new System.Runtime.InteropServices.RegistrationServices(); if (!regSrv.RegisterAssembly( this.GetType().Assembly, AssemblyRegistrationFlags.SetCodeBase)) { throw new InstallException("Failed to register componenet for COM interop"); } } catch { }}
Well when this problem happened for the second time just this week when I switched my Outlook2OneNote project structure from being a simple Project that had all the logic to one that inherited from another class in another project I started wondering and thinking this has to be a bug. Well using my super hero powers I tracked this problem down and found a better work around.
Additionally, I've been told that custom actions should be avoided for a number of reasons. One good reason is that if you ever use the MSI in the future to upgrade your assembly, it will fail.
Approach 2: Simple workaround for bug
Rather than adding the Primary Output of the project that needs to be registered for COM Interop, do the following:
By adding your assembly directly to the MSI and not relying on the Custom Action workaround mentioned above, you can rely on the MSI to register your component for COM Interop.
BTW – IMHO, developing .NET components and exposing them as COM components is a nasty business and one that I NO LONGER ENJOY!!! I am writing this because it’s a bit therapeutic and I hope it helps someone else who is having this problem (rather than hurl my laptop against the wall).
update: I made some corrections to this post based on some feedback from Rob Mensching.