VB.net avoiding cross thread exception with extension method

Posted by user574632 on Stack Overflow See other posts from Stack Overflow or by user574632
Published on 2011-01-13T18:03:31Z Indexed on 2011/01/13 20:53 UTC
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Hello I am trying to implement a solution for updating form controls without using a delegate.

I am attempting to use the 1st solution on this page:

http://www.dreamincode.net/forums/blog/143/entry-2337-handling-the-dreaded-cross-thread-exception/

Imports System.ComponentModel
Imports System.Runtime.CompilerServices

Public Module MyInvoke
    <Extension()> _
    Public Sub CustomInvoke(Of T As ISynchronizeInvoke)(ByVal control As T, ByVal toPerform As Action(Of T))
        If control.InvokeRequired Then
            control.Invoke(toPerform, New Object() {control})
            toPerform(control)
        End If
    End Sub
End Module

The site gives this as example of how to use:

Label1.CustomInvoke(l => l.Text = "Hello World!")

But i get 'l' is not declared error. As you can see im very new to VB or any OOP.

I can get the second solution on that page to work (using delegates) but i have quite a few things to do in this thread and it seems like i would need to write a new delegate sub for each thing, which seems wasteful.

What i need to do is select the 1st item from a combobox, update a textbox.text with the selected item, and pass the selected item to a function. Then wait for x seconds and start again, selecting the second item.

I can get it to work in a single threaded application, but i need the interface to remain responsive.

Any help greatly appreciated.

EDIT: OK so changing the syntax worked for the example. However if i change it from

Label1.CustomInvoke(Sub(l) l.text = "hello world!")

(which worked just fine) to:

Dim indexnumber As Integer = 0
ComboBox1.CustomInvoke(Sub(l) l.SelectedIndex = indexnumber)

I get a cross threading error as though i didnt even use this method:

Cross-thread operation not valid: Control 'ComboBox1' accessed from a thread other than the thread it was created on.

So now im back to where i started? Any further help very much appreciated.

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