ProjectExtension is the base class for buidling project extensions within application framework. By inheriting ProjectExtension, you can modify properties or behavior of existing tasks to fit your field workflow, or create new workflow to embed your business logic.

A common question for building project extensions is "how do I plug in to the mobile application"? Well, Project class provides three methods that will be called one after the other - Initialize, OnOwnerInitialized, and Uninitialize. You can override these methods to plug in your implementation to the application. The Initialize method will be called when the Project is initializing. At this point you are guaranteed that all other Tasks and ProjectExtensions have been instantiated. OnOwnerInitialized method is called by the Project when it is initialized, and all other Tasks and ProjectExtensions will have been initialized at this point. The Uninitialize method is called by the Project before the Project is closed, giving you the opportunity to cleanup things such as detaching events from application level objects.

Note that, to use a ProjectExtension, you will need to prepare an ame file that describes your ProjectExtension. There are also different optioins for you to deploy your assembly and the ame file. For more details please refer to developer help.

System.Object
   ESRI.ArcGIS.Mobile.Client.Extension
      ESRI.ArcGIS.Mobile.Client.ProjectExtension
         ESRI.ArcGIS.Mobile.Client.Extensions.ExtensionManager.ExtensionManagerExtension
         ESRI.ArcGIS.Mobile.Client.Extensions.MapLayerManager.MapLayerManagerExtension
         ESRI.ArcGIS.Mobile.Client.Task

Reference