Can Excel UDFs Modify Other Cells?

Excel UDF: Overcoming Limitations in Array Output

Excel User-Defined Functions (UDFs) typically return a scalar value, but what if you require a UDF to modify other cells? This is challenging because UDFs are expressly forbidden from altering any cell, worksheet, or workbook properties.

Is It Possible?

Contrary to popular belief, it is possible to accomplish this task, albeit through a complex workaround. By leveraging a combination of Windows timer and Application.OnTime timer, we can bypass these limitations.

Understanding the Workaround

The Windows timer is initiated from within the UDF. However, its function is limited to scheduling an Application.OnTime timer. The Application.OnTime timer, which is Excel-approved, executes safely only when no cell is being edited and no dialogs are open.

Implementation

To implement this workaround, place the following code in a regular module:

[Code Goes Here]

Detailed Explanation

1. AddTwoNumbers UDF:

   • The UDF calculates the sum of two numbers.
   • It also caches the caller's cell reference and starts a Windows timer to trigger subsequent tasks.

2. AfterUDFRoutine1:

   • This timer routine stops the Windows timer.
   • It then schedules an Application.OnTime timer using a safe timer.

3. AfterUDFRoutine2:

   • This timer routine is triggered by the Application.OnTime timer.
   • It performs tasks that are not allowed within a UDF, such as modifying other cell values.

Conclusion

While Excel restricts UDFs from directly altering cells, this workaround provides a solution. By utilizing a Windows timer and an Application.OnTime timer in sequence, you can overcome these limitations and enable your UDF to perform actions that would otherwise be impossible.

The above is the detailed content of Can Excel UDFs Modify Other Cells?. For more information, please follow other related articles on the PHP Chinese website!