vb.net undertanding invoke/delegate

Discussion in 'Application Software' started by Stannieman, Jul 5, 2010.

  1. Stannieman

    Stannieman MDL Guru

    Sep 4, 2009
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    #1 Stannieman, Jul 5, 2010
    Last edited by a moderator: Apr 20, 2017
    Hi, I'm trying to show text in a label and disable/enable buttons etc from within a backgroundworker.
    I'm aware of the fact that just puting
    Code:
    lblLabel.text = ""
    in the backgroundworker sub will result in an error because the label isn't updated from the form tread.

    I read a bit on the web about invoking but I can't get it to work. It will probable work by just copy past the code from the web but I can't do anything with that in the future if I don't understand what that code is doing.

    So I made test project with a form with 1 label and 1 button and this code:
    Code:
    Public Class Form1
        Private Delegate Sub delegateInvoke()
        Dim delegateInvoketest As delegateInvoke
    
        Private Sub btnStart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnStart.Click
            bkgInvokeTest.RunWorkerAsync()
        End Sub
    
        Private Sub bkgInvokeTest_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles bkgInvokeTest.DoWork
            delegateInvoketest = New delegateInvoke(AddressOf updatelabel)
            delegateInvoketest.Invoke()
        End Sub
    
        Private Sub updatelabel()
            lblReport.Text = "hello world"
        End Sub
    End Class
    This isn't working cause I still get the error about crosstread stuff, but it's almost directly copy past.
    Is there anyone who can tell me how I should do this?

    EDIT: Topic title should be vb.net underStanding...
     
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  2. Stannieman

    Stannieman MDL Guru

    Sep 4, 2009
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    OK managed to do it using progresschanged.
    I think it's not the best/cleanest way to do it, but at least it works and I undertand how that works.
     
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