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Chapter 13: Extending Visual Studio 2010 379
It’s like people from different countries trying to communicate, where they have a subject
to discuss but need a common language to be able to understand each other; the common
language would be the interface between the people.
The first interface to discuss is IDTExtensibility2, whose purpose is to let VS manage
loading and unloading of the Add-In. Loading and unloading are important because VS
loads Add-Ins when it starts and unloads Add-Ins when it shuts down. There are certain
actions that you might want to take, depending on when the Add-In is loaded and what
type of information you might need access to. For example, the very first time an Add-In
is ever loaded, you might want to perform a special operation like configuration or asking
the user if she would like to register your Add-In. Table 13-1 shows the members of
IDTExtensibility2 and describes their purpose.
The second interface that Connect implements is IDTCommandTarget. When building an
Add-In, you need a way for the VS IDE to execute the Add-In. For example, you will create
a named command that exposes the Add-In as a menu item in the Tools menu. Whenever
a user selects the menu item, the named command will execute and run your Add-In code.
IDTCommandTarget is the interface VS uses to execute your Add-In. Table 13-2 shows the
members of IDTCommandTarget and describes their purpose.
Each of the methods of both the IDTExtensibility2 and IDCommandTarget interfaces are
implemented by the provided Connect class. Listing 13-1 shows each of these members with
full documentation comments and skeleton code. The code in Listing 13-1 is in C#, but it is
very informative to take the overview of the interfaces from the previous table and then
Table 13-1 The IDTExtensibility2 Interface
Member Purpose
OnAddInsUpdate Add-In is either loaded or unloaded.
OnBeginShutdown Add-In is running and VS shuts down.
OnConnection Add-In is loaded.
OnDisconnection Add-In is unloaded.
OnStartupComplete VS has started up and then Add-In is loaded.
Table 13-2 The IDTCommandTarget Interface
Member Purpose
Exec Called by VS to execute your Add-In.
QueryStatus Called by VS to determine if the command should be enabled,
invisible, or supported.