Question

Multi-Thread VB.NET application

Asked by: Nonamerz

Subj: Multiline VB.NET application

Hi there!

I need to find out how to operate with delegates in VB.NET; especially I need the universal example of the following:

- how to change text for TextBox'a
- how to clear ComboBox
- how to add Item in ComboBox

Thanks!

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Asked On
2009-09-17 at 08:07:37ID24740089
Tags

Thread VB.NET delegate Invoke

Topics

Microsoft Visual Basic.Net

,

C# Programming Language

,

.NET

Participating Experts
2
Points
500
Comments
10

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Answers

 

by: VBRocksPosted on 2009-09-17 at 08:33:09ID: 25357341

Here's an example of using a delegate to make thread-safe calls to windows forms controls:

    Private Delegate Sub mSetTextDelegate(ByVal txt As String)
    Private Sub SetText(ByVal txt As String)

        If Me.InvokeRequired Then

            Dim d As New mSetTextDelegate(AddressOf SetText)
            Me.Invoke(d, New Object() {txt})

        Else
            Me.TextBox1.Text = txt
        End If
    End Sub



'When you want to set the text from another thread:

    Private Sub Go()
        SetText("test")
    End Sub



For more information:
http://msdn.microsoft.com/en-us/library/ms171728(VS.80).aspx

 

by: ChaosianPosted on 2009-09-17 at 08:48:37ID: 25357522

Yeah. What VBRocks said! :)

Except that you I might argue a bit with the naming convention for his delegate. It makes it kind of confusing -- kind of makes the dele gate declaration looks like it's a variable. But I'm just picky that way.

 

by: NonamerzPosted on 2009-09-17 at 09:15:55ID: 25357846

Yes I saw similar examples before, but I need for universality e.g. I have 10 TextBoxes, but do I really have to write 10 times the same procedure as SetText?

 

by: ChaosianPosted on 2009-09-17 at 09:39:36ID: 25358126

Nope. Just pass the text box to update into the function. Something like this:

Private Delegate Sub SetTextDelegate(target As TextBox, ByVal txt As String)
 
Private Sub SetText(target As TextBox, ByVal txt As String)
        If target.InvokeRequired Then
            Dim d As New mSetTextDelegate(AddressOf SetText)
            Me.Invoke(d, New Object() {target, txt})
        Else
            target.Text = txt
        End If
End Sub

                                              
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by: NonamerzPosted on 2009-09-17 at 09:56:21ID: 25358340

Excellent
How do I Clear ComboBox and how to get the text from the textBox using this code?

 

by: ChaosianPosted on 2009-09-17 at 10:06:47ID: 25358472

Getting the text box should be thread-safe, so you should be able to just read it.

However, here's the code you've asked for.

	Private Delegate Function ReadTextDelegate(ByVal target As TextBox) As String
	Private Function ReadText(ByVal target As TextBox) As String
		If target.InvokeRequired Then
			Dim d As New ReadTextDelegate(AddressOf ReadText)
			Return Me.Invoke(d, New Object() {target})
		Else
			Return target.Text
		End If
	End Function
 
	Private Delegate Sub ClearComboBoxDelegate(ByVal target As ComboBox)
	Private Sub ClearComboBox(ByVal target As ComboBox)
		If target.InvokeRequired Then
			Dim d As New ClearComboBoxDelegate(AddressOf ClearComboBox)
			Me.Invoke(d, New Object() {target})
		Else
			target.Items.Clear()
		End If
	End Sub
                                              
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by: VBRocksPosted on 2009-09-17 at 10:11:49ID: 25358532

Hey Chaosian!  Long time since we've been on the same thread!  I hope all is well.

My original example is didn't target naming conventions, but just provided an overall example of how the process works.

 

by: NonamerzPosted on 2009-09-17 at 10:18:12ID: 25358621

And how to use it? I thought so
Dim cb As ComboBox
ClearComboBox (cb.Items.Clear)

 

by: ChaosianPosted on 2009-09-17 at 10:19:18ID: 25358638

ClearComboBox(cb)

 

by: ChaosianPosted on 2009-09-17 at 10:29:20ID: 25358750

I'd really be a lot happier if VBRocks got most of the points on this one. I only tweaked the correct answer they gave.

20120131-EE-VQP-002

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