How to break a loop with a single button click - vb.net

Question

I am using VB.NET and I have:
a Start button
a Stop button
a While loop
When the Start button is pressed, the While loop begins. I want to stop the loop when the Stop button is pressed.
I had tried to use Applications.DoEvents, but the loop stops when the Stop button is pressed twice.
Below is my code using Applications.DoEvents
Dim stopclick As Boolean = False
Private Sub btnPlay_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnPlay.Click
btnForward.Enabled = False
btnStop.Enabled = True
While
' Perform the while statements
If stopclick = True Then
stopclick = False
Application.DoEvents()
Exit While
End If
End While
End Sub
Private Sub btnStop_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnStop.Click
stopClick = True
End Sub
Have I used Application.DoEvents incorrectly?
What are the other options besides Application.DoEvents? How can I stop the loop with a single Stop button click?

Answer 1

You need to put the call to Application.DoEvents outside of your If statement, like this:
While True
Application.DoEvents()
' Perform the while statements
If stopclick Then
stopclick = False
Exit While
End If
End While
The Stop_Click won't have a chance to be processed until you call DoEvents, so, with the way you had it, stopClick would never get set to True.
However, the larger issue, here, is that calling DoEvents, at all, is very bad practice and can lead to some very difficult-to-fix bugs if you aren't very careful. It would be far better if the loop was performed in a background thread. Check out the BackgroundWorker component for an easy to implement threading mechanism for WinForm projects. You'll find it in the tool box of your form designer.
Here's an example of how to do it with the BackgroundWorker component:
Dim stopclick As Boolean = False
Private Sub btnPlay_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnPlay.Click
btnForward.Enabled = False
btnStop.Enabled = True
BackgroundWorker1.RunWorkerAsync()
End Sub
Private Sub btnStop_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnStop.Click
stopClick = True
End Sub
Private Sub BackgroundWorker1_DoWork(sender As Object, e As DoWorkEventArgs) Handles BackgroundWorker1.DoWork
stopClick = False
While Not stopClick
' Perform the while statements
End While
End Sub
Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
btnForward.Enabled = True
btnStop.Enabled = False
End Sub

Answer 2

You can simplify your while loop significantly by using stopClick as your condition:
While Not stopClick
Application.DoEvents()
End While

Answer 3

I know this is an old thread, but I found a simple workaround. Add a CheckBox to the form (it can even be "off the side of the form," if that made sense).
Private Sub btnStopLoop_Click(sender As System.Object, e As System.EventArgs) Handles btnStopLoop.Click
chkEndLoop.CheckState = CheckState.Checked
End Sub
Then, in the Loop you wish to exit:
Do Until chkEndLoop.CheckState = CheckState.Checked
'Do Stuff Here
Loop
As long as the CheckBox.CheckState = CheckState.Unchecked, the Loop will continue, but when the CheckBox becomes Checked, the Loop will Exit

Answer 4

You have to use btnstop.focus() at the start of the loop. This will be sure to solve your problem.
Example:
Dim stopclick As Boolean = False
Private Sub btnPlay_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnPlay.Click
btnForward.Enabled = False
btnStop.Enabled = True
btnStop.Focus() ' new code---------------------
While
' Perform the while statements
If stopclick = True Then
stopclick = False
Application.DoEvents()
Exit While
End If
End While
End Sub
Private Sub btnStop_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnStop.Click
stopClick = True
End Sub