Tristate checkbox in Office ribbon

Question

Is there a way to have a tri-state checkbox on MS office 2016 ribbons?

Answer 1

Nope. The Fluent UI has a limited number of controls with a pre-defined functionality. You can find all the ribbon UI controls described in the following articles:

• Customizing the 2007 Office Fluent Ribbon for Developers (Part 1 of 3)
• Customizing the 2007 Office Fluent Ribbon for Developers (Part 2 of 3)
• Customizing the 2007 Office Fluent Ribbon for Developers (Part 3 of 3)

The checkBox control provides the getPressed callback which returns boolean:

C#: bool GetPressed(IRibbonControl control)
VBA: Sub GetPressed(control As IRibbonControl, ByRef returnValue)
C++: HRESULT GetPressed([in] IRibbonControl *pControl, [out, retval] VARIANT_BOOL *pvarfPressed)
Visual Basic: Function GetPressed(control As IRibbonControl) As Boolean

There is no third state.