XL: How to Run a Macro When Certain Cells Change

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Microsoft provides programming examples for illustration only, without warranty either expressed or implied. This includes, but is not limited to, the implied warranties of merchantability or fitness for a particular purpose. This article assumes that you are familiar with the programming language that is being demonstrated and with the tools that are used to create and to debug procedures. Microsoft support engineers can help explain the functionality of a particular procedure, but they will not modify these examples to provide added functionality or construct procedures to meet your specific requirements. In many instances, a macro should run only when a certain number of cells have values entered into them (referred to as the "key cells" in this document). In order to prevent a large macro from running every time a value is entered into a cell of a sheet, you must check to see if the ActiveCell is one of the key cells. To accomplish this, use the Intersect method on the ActiveCell and the range containing the key cells to verify the ActiveCell is one of the key cells. If the ActiveCell is in the range containing the key cells, you can call the macro.

To run this sample macro:

1. Open a new workbook.
2. On Sheet1 in cell A11, type the following formula:

   =SUM(A1:A10)

3. Copy this formula to cells B11, C11, and D11.
   
   In the example used here, the macro causes the background color of cells A11, B11, and C11 to change to red (or ColorIndex 3) if that cell's value is larger than 50; otherwise, the cell's background color will be normal. This is accomplished by checking for entries in cells A1:A10, B1:B10, and C1:C10. Each time an entry is made in any cell on Sheet1, the DidKeyCellsChange macro runs. This macro determines if the ActiveCell is in the range of key cells (A1:C10). If it is, the KeyCellsChanged macro is called to re-evaluate cells A11:C11.
   
   The following macros work together to perform this functionality. The "Auto_Open" macro must be run once in order for the other macros to be called.
4. Insert a new module sheet. In Microsoft Excel 97, on the Tools menu, point to Macro, and then click Visual Basic Editor. In the Editor, click Module on the Insert menu. In Microsoft Excel versions 5.0 and 7.0, point to Macro on the Insert menu, and then click Module.
5. Type the following macro code into the module sheet:

   Sub auto_open()
   
      ' Run the macro DidCellsChange any time a entry is made in a
      ' cell in Sheet1.
      ThisWorkbook.Worksheets("Sheet1").OnEntry = "DidCellsChange"
   
   End Sub
   
   
   Sub DidCellsChange()
     Dim KeyCells as String
      ' Define which cells should trigger the KeyCellsChanged macro.
      KeyCells = "A1:A10, B1:B10, C1:C10"
   
      ' If the Activecell is one of the key cells, call the
      ' KeyCellsChanged macro.
      If Not Application.Intersect(ActiveCell, Range(KeyCells)) _
      Is Nothing Then KeyCellsChanged
   
   End Sub
   
   Sub KeyCellsChanged()
      Dim Cell as Object
      ' If the values in A11:C11 are greater than 50...
      For Each Cell In Range("A11:C11")
      If Cell > 50 Then
   
      ' Make the background color of the cell the 3rd color on the
      ' current palette.
      Cell.Interior.ColorIndex = 3
   
      Else
      ' Otherwise, set the background to none (default).
      Cell.Interior.ColorIndex = xlNone
   
      End If
      Next Cell
   
   End Sub

6. Save the workbook, and then close it.
7. Open the workbook.
   
   This will cause the Auto_Open macro to run.
8. In cell A1, type 60.
   
   Cell A11 should change to a Red background color because you changed a cell in the KeyCells range and the value of cell A11 became greater than 50.
9. In cell D1, type 60
   
   Nothing will happen to the color of D11, even though the value in D11 is now greater than 50. Nothing happens because cell D1 is not in the KeyCells range.