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How Microsoft Excel Finds the OnePager Express Add-In

When OnePager Express is run as a COM Add-In, it is vital that Excel find the OnePager Express program when it starts up. Otherwise the buttons that launch OnePager will not appear on the toolbar. This FAQ gives a technical description of how this works. Everything happens in the Windows registry, and you can observe this registry information by running the Microsoft program regedit. Excel discovers OnePager Express by using the following key in the registry:


Where HIVE=HKEY_CURRENT_USER for a per-user installation and HIVE=HKEY_LOCAL_MACHINE for a per-machine installation.

This key is placed in the registry during the OnePager installation process. Under this key, LoadBehavior=3 causes the OnePager buttons to appear every time Excel is launched. LoadBehavior=2 means either that the user has disabled OnePager or that an error has occurred when Excel attempted to load OnePager.

The string CG_XL_Addin.OnePagerXL is called the ProgID in Microsoft COM terminology. Once Excel knows the ProgID, it looks in the registry to find the ClassID for OnePager Express, which has the value {EBCCDF16-59CE-40AE-8155-B0DE24BA0E44}. Using this ClassID, Excel retrieves the path to the binary files and executes them to place the buttons on the ribbon or toolbar.

Last Updated: August 10, 2021