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| Title | Allow the user to start and stop a long process |
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| Keywords | long process, start, stop |
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| Categories | Software Engineering |
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Use a form-level Boolean variable Running to tell the procedure when to stop. The RunLongProcess subroutine is the long process in this example. It periodically calls DoEvents to let the program process button clicks and then checks Running to see if it should still be running.
The CmdStart_Click event handler checks Running to see if the long process is currently running. If the process is running, the user is trying to stop the process so the program sets Running to False to tell RunLongProcess to stop.
If the process is not running, the user is trying to start it. The program sets Running = True and calls RunLongProcess.
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Private Running As Boolean
Private Sub RunLongProcess()
Dim i As Long
i = 1
Do While Running
i = i + 1
CountLabel.Caption = Format$(i)
DoEvents ' Very important!
Loop
End Sub
Private Sub CmdStart_Click()
If Running Then
' The process is running. Stop it.
Running = False
CmdStart.Caption = "Stopping"
CmdStart.Enabled = False
Else
' The process is not running. Start it.
' Prepare the button.
CmdStart.Caption = "Stop"
DoEvents
' Perform the long process. It will stop
' when Running is False. That happens when
' RunLongProcess calls DoEvents and the
' user has clicked Stop. At that point
' this routine is called again and the code
' above runs, changing the button's caption
' and disabling it.
Running = True
RunLongProcess
CmdStart.Caption = "Start"
CmdStart.Enabled = True
End If
End Sub
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