The Visio 2010 SDK contains the following items to help you develop custom solutions for Visio 2010:
Code Samples Library--Provides a database of reusable Visio code samples.
Flowchart sample application--Shows how to create a Component Object Model (COM) add-in that automates the creation of a flowchart drawing from an Excel spreadsheet.
TreeView sample application--Shows how to create a hierarchical drawing and its accompanying tree view in Visio. Office Plan sample application--Shows how you can use the Visio 2010 Drawing Control to create an application that takes advantage of the drawing features of Visio 2010 in a Microsoft Windows Form.
VSTO Add-in sample application--Shows how to create an add-in, based on Microsoft Office development tools in Microsoft Visual Studio 2010, that includes custom Visio content and is deployed by using ClickOnce installation.
Note : The Office development tools in Visual Studio were known as the Visual Studio Tools for Office (VSTO) in previous versions of Visual Studio. Tools
Persistent Events tool--Provides a user interface that lets you add persistent events in an active Visio document and modify existing persistent events.
Solution Publishing tool--Lets you add Visio-specific entries to the PublishComponent table of a Windows Installer (.msi) file for publishing custom Visio content. Type libraries
The Visio SDK provides three type libraries that Visio 2010 exposes. In addition, it provides support files to help C++ developers automate Visio. Add-on wizards
The Visio SDK installs wizards for creating Visio add-on projects in Microsoft Visual Studio 2005 and Microsoft Visual Studio 2008 Documentation