Question

I have a weird problem where Excel is behaving differently on my development machine and a testing machine.

In my add-in, I’ve turned off ScreenUpdating in several places for long running processes. On my machine this works fine. On the testing machine, Excel sets ScreenUpdating = true as soon as I write to a cell.

The following code demonstrates the issue for me.

private void ThisAddIn_Startup(object sender, System.EventArgs e)
{
    Microsoft.Office.Interop.Excel.Application excel = Globals.ThisAddIn.Application;

    MessageBox.Show(excel.ScreenUpdating.ToString());

    excel.ScreenUpdating = false;
    MessageBox.Show(excel.ScreenUpdating.ToString());

    Workbook workbook = Globals.ThisAddIn.Application.ActiveWorkbook;
    Worksheet w = (Worksheet)workbook.Worksheets[1];
    ((Range)w.Cells[1, 1]).Value = "Test";
    MessageBox.Show(excel.ScreenUpdating.ToString());
}

On my machine, opening Excel gives three message boxes saying

“True”, “False”, “False”.

On the test machine they say

“True”, “False” and “True”.

I’ve also stepped through with a remote debugger and watched the ScreenUpdating property change immediately after the cell value is set. Further, this isn’t the only thing that resets ScreenUpdating. Adding or removing a Worksheet or Workbook will also do this.

The Excel version on each system is the same (14.0.6112.5000 (32-bit)).

What could be causing this? How can I fix it so that Excel respects my settings?

Answer 1

Other addins in Excel can interfere with that single global setting.

It is for that reason you are supposed to save the current ScreenUpdating state to a local variable before, and restore it after, each use.

Ignore the changing of that setting in the ThisAddIn_Startup event (as you would not normally do your work there anyway).