Stop Button

MDavid Johnson

14y1.8k

I need to use a "Run" button and a "Stop" button to control the execution of an internal subroutine. The following code works, but you have to click the Stop button twice to stop the routine. What do I have to do to get it to stop in a single click?

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' RunTest.exe
' Version 1.0.0
' MDJ 2012/06/27

' Label1 initially displays "STOPPED"

Option Strict On

Imports System.Windows

Public Class Form1

    ' Global Variable
    Public runControl As Boolean

    ' Run Button
    Private Sub RunButton_Click(sender As System.Object, e As System.EventArgs) Handles RunButton.Click
        runControl = True
        Label1.Text = "RUNNING"
        While runControl = True
            RunStep()
        End While
    End Sub

    ' Stop Button
    Private Sub StopButton_Click(sender As System.Object, e As System.EventArgs) Handles StopButton.Click
        ' With this configuration, the Stop button must be clicked twice before the While Loop will exit ???
        runControl = False
        Label1.Text = "STOPPED"
    End Sub

    Public Sub RunStep()
        Dim ValueHolder As Integer

        ' Process some data
        For i = 1 To 79
            For j = 1 To 79
                ValueHolder = i * j + 23
            Next
        Next

        ' Allow outside events to be processed
        Application.DoEvents()

    End Sub
End Class

2 Replies

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Vulpes14y ago
Accepted answer
Where possible, I'd avoid Application.DoEvents which (as here) can produce unexpected behaviour.

As the code in the RunStep() method will execute very quickly, a BackgroundWorker or multi-threading is not very suitable either.

What I'd suggest you do instead is to use a timer with a short interval, say 60 milliseconds. This doesn't use much in the way of resources and all the code will continue to execute on the user interface thread

So, I'd add a timer to your form, double click on it to add a Tick handler and change your code as follows:

Public Class Form1

' Run Button
Private Sub RunButton_Click(sender As System.Object, e As System.EventArgs) Handles RunButton.Click
Label1.Text = "RUNNING"
Timer1.Interval = 60
Timer1.Start()
End Sub

' Stop Button
Private Sub StopButton_Click(sender As System.Object, e As System.EventArgs) Handles StopButton.Click
' should now get called on first click
Timer1.Stop()
Label1.Text = "STOPPED"
End Sub

Public Sub RunStep()
Dim ValueHolder As Integer

' Process some data
For i = 1 To 79
For j = 1 To 79
ValueHolder = i * j + 23
Next
Next
End Sub

Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
RunStep()
End Sub

End Class
MDavid Johnson14y ago
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Hi MDavid Johnson,
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Thank you, but none of those articles appear to address my issue.