vb.net - Stop loop when I press Button

Question

I have a loop (in another class) what I want stop when I press a button, but I don't know how to do it

This is my code:

'My FORM

Dim blStop = False

Private Sub btnFilter_Click(sender As Object, e As EventArgs) Handles btnFilter.Click
        AnotherClass.doTheLoop(blStop)
End Sub

Private Sub btnStop_Click(sender As Object, e As EventArgs) Handles btnStop.Click
        blStop = True
End Sub



'AnotherClass Loop

While (blStop = False)
    'blablabla
End While

What's the line that declares blStop? Also your `AnotherClass` definition shouldnt include the parameter `blstop`. Your code in the class will treat it as a local variable, not the variable that was defined outside the class. — David Wilson, May 03 '16 at 09:59
@MattWilko this is the code: Public Sub doTheLoop(blStop as Boolean) While (blStop = False) 'blablabla End While End Sub — cnbandicoot, May 03 '16 at 10:20
Ok add a boolean property to your Another class called Cancel Set that in your button click and handle it in the loop. — David Wilson, May 03 '16 at 10:25

score 1 · Accepted Answer · answered May 03 '16 at 10:44

1

your issue is this:

Public Sub doTheLoop(blStop as Boolean) 
    While (blStop = False) 
       'blablabla 
    End While 
End Sub

The declaration of blStop, creates a new variable, so when you set, the value to False, you only set the one decalred locally.

A quick and dirty fix would be to declare the boolean ByRef - that would mean that it will still reference the original variable.

Public Sub doTheLoop(ByRef blStop as Boolean) 
    While (blStop = False) 
       'blablabla 
    End While 
End Sub

A better solution would be to have a method in your class that you call when you want to stop rather than passing round variables.

answered May 03 '16 at 10:44

Matt Wilko

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That loop will never stop because it is called by UI thread... UI will freeze until loop is over so user will never be able to press button to stop the loop... – Martin Verjans May 03 '16 at 13:17
@SuperPeanut - depends what is in `'blablabla ` – Matt Wilko May 03 '16 at 13:29

score 1 · Answer 2 · answered May 03 '16 at 11:42

Here is how your other class should look like :

Public class AnotherClass
    Private Shared blStop As Boolean = False

    'blablabla

    Public Shared Sub doTheLoop()
        While Not blStop
            'blablabla
        End While
    End Sub

    Public Shared Sub StopTheLoop()
        blStop = True
    End Sub

    'blablabla
End Class

Then you can call this loop like this :

'Form class
Private Sub btnFilter_Click(sender As Object, e As EventArgs) Handles btnFilter.Click
    'You must run the loop on another thread or you will block the UI thread. 
    'Therefore your application will 'Stop Responding'
    System.Threading.Thread.QueueWorkUserItem(AddressOf(AnotherClass.DoTheLoop))
End Sub

Private Sub btnStop_Click(sender As Object, e As EventArgs) Handles btnStop.Click
    AnotherClass.StopTheLoop()
End Sub

vb.net - Stop loop when I press Button

2 Answers2