Expert: Aaron Young - 4/14/2005

Question
What is the DoEvents Function used fore

Answer
Curt,

DoEvents is used to force the application to yield it's use of the processor for one cycle (usually 50ms), it's commonly used to allow other events in your application to fire while you're performing a resource intensive operation.

Here's an example, this code causes the Form's Caption to Count from 1 To 10,000 and also checks to see if you've decided to cancel it by clicking the "Cancel" button.

Run the code with the "DoEvents" line commented out first and you'll notice that you can't click the "Cancel" button to cancel the count.  This is because the loop isn't allowing anything else in your application to use the processor.

Now run the same code again, but this time uncomment the "DoEvents" line, now you'll see that you can cancel the loop at any time without a problem.

'--------------------------------------------------------
Option Explicit

Private m_cancel As Boolean

Private Sub cmdStart_Click()
  Dim i As Long
  m_cancel = False
  For i = 1 To 10000
     Caption = i
     DoEvents
     If m_cancel Then Exit For
  Next
End Sub

Private Sub cmdCancel_Click()
  m_cancel = True
End Sub
'--------------------------------------------------------

Regards,

- Aaron.