Monday, November 26, 2007

* VSTO : How Office add-ins get loaded ?

  • The main component responsible for loading add-ins is Add-In Loader AddinLoader.dll which gets installed with Visual Studio Tools for Office Runtime.
  • When any Office client application starts it looks for all the add-ins registered in registry.
  • The registry provides location of Application manifest file for each add-in.
  • The Application manifest file contains mainly following information :
    • Version of the add-in
    • Location of Deployment manifest
    • Version, location name of assemblies used by the add-in.
  • If Deployment Manifest(DM) is mentioned, the version numbers of Application manifest(AM) and deployment manifest are compared. If DM is of newer version than AM, this means the add-in has been upgraded and new AM is loaded whose location is mentioned in DM.
  • If no upgrade is required, add-in assemblies are loaded by the runtime.
  • For each add-in, runtime creates a separate application domain to load assemblies. This provides better isolation.
  • Add-in assemblies are executed and ready to receive inputs from users or event notifications from office application.


What's New in VSTO 2008 v3.0

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