Professional Visual Studio® 2008

52.4. The Structure of .AddIn Files

Besides the add-in assembly, which is like its heart and contains all its implementation, there is also an XML file that acts as its configuration file with an .AddIn extension. This .AddIn file was first introduced in Visual Studio 2005 to simplify the process of add-in deployment. Prior to this version, you had to register the add-in COM component to deploy it, and this had its own difficulties. But now, thanks to .AddIn files, deployment is much easier.

An .AddIn file is an XML file with a specific schema that is defined by the http://schemas.microsoft.com/AutomationExtensibility namespace. When you create an XML file and set its XML namespace to this, Visual Studio automatically gives you IntelliSense to work with .AddIn files and edit them easily.

Like any other XML file, .AddIn files have their own special structure and format. Discussing all elements and attributes of this file is beyond the scope of this book, but you can find a detailed discussion about this file in Chapter 6 of Professional Visual Studio Extensibility (ISBN: 9780470230848).

Here in a nutshell is an introduction to the structure.

An .AddIn file has an <Extensibility /> root element, which contains two possible child elements including <HostApplication /> and <Addin />.

<HostApplication /> defines a host application for an add-in and <Addin /> configures the add-in with some information about it to set it up. Visual Studio looks into these elements to find the necessary ...