ExtraSharedProps is an internal mechanism used to support extra properties that may be shared among tools derived from the existing tool classes. The operation of ExtraSharedProps does not change the properties of the SharedProps object. ExtraSharedProps is only useful for developers who are deriving their own tools from this class; its operation is transparent to the developer who is simply using the existing features of the control in their application.
Each tool type that wants to store another extra shared props object should override ExtraSharedPropsCount, and in the get accessor, call the base implementation, add one, and return that new number. When accessing the custom extra shared props object, the tool type should use the value of ExtraSharedPropsCount from the base implementation and pass that as the index parameter into either GetExtraSharedProps or SetExtraSharedProps.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Server 2012, Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2