SSMS 2008 add-ins: one problem solved

If you Google SQL Server Management Studio Add-Ins, you'll find quite a few articles on writing them for SSMS 2005.  You'll also find people complaining that they can't get them to work in 2008.

I can't add any useful comment on the changes made in assemblies between versions, because I didn't attempt writing an SSMS add-in until I'd already upgraded to 2008.  However, I did encounter one problem right away when I attempted to write an SSMS version of a VS 2010 add-in, as have others.  The boilerplate code in the OnConnect method, which was generated by VS, would fail on this line:

     public void OnConnection(object application, ext_ConnectMode connectMode, object addInInst, ref Array custom)

     {

           _applicationObject = (DTE2)application;                      

           _addInInstance = (AddIn)addInInst;

The error message was “No such interface supported”.

A little poking about, and it became clear that this is because, well, the host application isn't a DTE2 anymore.  It's a SSMS object with a very long name and no obvious connection to the DTE2.  Which is a problem if you need any of the DTE2's properties, as you probably do.  

But the fix is easy.  The addInInst object has a DTE property that is, in fact, of type DTE2!  So all you have to do to get over this speed bump is to change those two assignment statements:

    _addInInstance = (AddIn) addInInst;                                    

    _applicationObject = (DTE2) _addInInstance.DTE;

And carry on from there.