It depends on what the definition of "this" is
I was perusing the VSTO MSDN forum a couple days ago and I saw Add a command button to the send email screen. This person (Bear23 to be exact) wanted to add a button to an Outlook 2003 Inspector. Well, not only do I know how to do this, but I have code I know works. I have Office 2007 and VSTO 2005 SE on both of my main computers, so I fire up my VPC with Office 2003 and VSTO. I create a new VSTO Outlook project, add my existing code, confirm it works and post the code.
Bear23 writes back that my code doesn't work and yields an error on the following code:
openInspectors = this.Inspectors;
The error is ThisAddIn does not contain a definition for 'Inspectors'
The code works on my machine, but not Bear23's. So yesterday ends with both of us confused.
This morning, I notice that in the post, Bear23 said that he or she is using VSTO 2005 SE. I have VSTO 2005 on my VPC. So I install VSTO 2005 SE and what do you know, my code now yields the same error.
In VSTO 2005, you have one option for creating Outlook 2003 Add-ins. You can select Office as the project type and Outlook Add-in as the template.
If you do this (and I did the first time), your project has a ThisApplication class and the code above works just fine. "this" refers to Outlook and Outlook has a collection of Inspectors.
If you install VSTO 2005 SE over VSTO 2005 you have two options for creating Outlook 2003 Add-ins. You can select 2003 Add-ins as the project type and Outlook Add-in as the template. If you only have VSTO 2005 SE, which is Bear23's situation, you only get this option.
If you choose this template (which Bear23 did), your project has a ThisAddIn class and the code above does not work. "this" refers to the add-in, not to Outlook. "this.Application" refers to Outlook and you use the following code:
openInspectors = this.Application.Inspectors;
So there are three different scenarios, and any given VSTO user will fall into one of them. Next time I give somebody code or use someone else's code, I should check to make sure we are in synch on which type of Add-in we are creating. You should too.