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I'm using the ExcelDNA library, which seems to use a combination of Excel's C-API and COM interface.

How are these interfaces different in terms of implementation by Excel? From the Microsoft site (https://msdn.microsoft.com/en-us/library/office/bb687829.aspx):

" Customizing the Excel User Interface

For many versions of Excel, the C API has not been the best choice for customizing the user interface. VBA has superior access to Excel objects and events. The user interface introduced in Excel 2007 is significantly different from earlier versions both in appearance and underlying technology. You can best customize this interface by using managed code resources."

What makes COM more suitable for editing Excel's UI than the C-API?

Zach Smith
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Its easier and faster to write user-interface stuff using VBA or .NET rather than C or C++.

The COM interface has access to a much richer set of Excel objects and events than the C-API interface but the C-API is preferred for writing UDFs because it performs substantially better than COM and allows things like multi-threading, async, RTD, cluster etc that COM does not offer.

Note that using COM from ExcelDNA means using COM-INTEROP which is inherently slow.

Charles Williams
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  • I think that ExcelDNA is using COM-INTEROP for Fluid Ribbon interactions, and the C-API for VBA. If this is correct, would that still be a problem? – Zach Smith Jan 05 '17 at 12:07
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    Excel-DNA does not work with VBA. Excel DNA allows you to use both C-API and COM-Interop in the same solution. Which you use depends on both on choice and the different features of the interfaces. Usually you exclusively use the C-API for all the UDF code and exclusively COM-Interop for everything else. – Charles Williams Jan 05 '17 at 12:16
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I agree with Charles regarding the ease and lower TCO of building UI components and quickly prototyping new features using C# and Excel DNA (or Addin Express to be fair).

Before declaring that performance is of paramount importance, do set some expectations and measure the calculations or events involved. If there is a truly performance sensitive section, isolate it and then write managed C++ code that could then be integrated with the UI written in C# or VB.NET.

Also, just a minor correction to Charles' comment regarding Excel DNA and VBA; they do work together. A couple of examples can be found at:

B1sh3r
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