A property sheet extension is a dynamic-link library (DLL) that adds one or more pages to a property sheet created by another module. The module that creates the property sheet includes an AddPropSheetPageProc callback function that the extension DLL calls to add a page. The function receives the handle of a page and an application-defined 32-bit value.
The extension DLL also contains a callback function called ExtensionPropSheetPageProc, which receives the address of AddPropSheetPageProc from the module that creates the property sheet. The extension DLL must export ExtensionPropSheetPageProc.
The Windows header files include two prototypes for defining property sheet callback functions. To define AddPropSheetPageProc, use the following prototype.
typedef BOOL (CALLBACK FAR * LPFNADDPROPSHEETPAGE)(HPROPSHEETPAGE,
LPARAM);
To define ExtensionPropSheetPageProc, use the following prototype.
typedef BOOL (CALLBACK FAR * LPFNADDPROPSHEETPAGES)(LPVOID, LPFNADDPROPSHEETPAGE, LPARAM);