Protecting Formulas in Control-Linked Cells

Michael has a form control (a check box) linked to cell A1. He can place a formula into cell A1 that resolves to True or False, and the check box reflects that result. However, if someone clicks on the check box to change it, the formula in cell A1 is overwritten by an explicit True or False. Michael needs the formula in cell A1 to control the check box, but he also needs the user to be able to toggle the check box without overwriting the formula. He wonders if this is possible.

In short, this is not possible. Microsoft intended check boxes to control the value in a cell, and then you could reference that cell in other formulas. They never intended for the linked cells to contain formulas.

One thing you could try, if you desire, is to create a macro that monitors a cell and, if it changes, update a different cell. For instance, you could tie your check box to a different cell (such as cell B1), so that the formula in cell A1 isn't affected when the check box is used. You an then create an event handler macro that examines whatever is in cell A1, and if it changes, then the macro modifies what is in cell B1. This modification in cell B1 will then trigger the change in the check box.

Another macro-based approach is to use a macro to write a formula into cell A1. This is a simple example of such a macro:

Sub CheckBoxState()
    Range("A1").Formula = "=IF(" & Range("A1") & _
      ",""CHECKED"",""NOT CHECKED"")"
End Sub

If you assign this macro to the check box control, then when a person clicks the check box, two things happen. First, the state of the check box is written to cell A1, overwriting whatever is there. Second, the macro is executed, writing the formula back into cell A1. Note that the formula (as defined in this macro) takes into account the value that was just stored in cell A1. Thus, if the check box control writes True into cell A1, then the macro stuffs the following into the cell:

=IF(TRUE,"CHECKED","NOT CHECKED")

Click the check box again, the value stuffed into the cell changes to False, and the formula that is placed into the cell changes. Of course, you would need to modify the macro so that the formula it forces into cell A1 reflects the formula you really want there.

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