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It is quite annoying when a .net program try to update user interface control from a seperate long run task thread.

The runtime give me exception “Control control name accessed from a thread other than the thread it was created on.”

If it is in visual studio 2005, a lot of place recommend use "BackgroundWorker" to solve the problem.

But it is also not flexiable, It works fine with progressbar control only. If I need to display something on textbox, It is not straigt forward. For example, I want to change textbox background color.

I created my own skeleton code which can easily access any user interface control from seperate thread.

The key part is in UpdateUI_handler subroutine.

And if you want to access one control, you just need tell

• what control you want to access,
• what property of the control you want to access,
• and what value you want to set.

That is very easy approach to solve the problem.

Below is my sample application snapshot

You can follow 3 steps below to create the project

1. Create vb winform application in visual studio 2005.
2. Drag a textbox, a label, a progressbar and a button on the form.
3. Copy the code below and overwrite form1.vb

   1:  Imports System

   2:  Imports System.Threading

   3:  Imports system.reflection

   4:  Public Class Form1

   5:      Delegate Sub UpdateUI(ByVal UpdateParameter As UIUpdateParameter)

   6:      Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

   7:          Dim index As Int32

   8:          index = 10

   9:          Me.ProgressBar1.Maximum = index

  10:          Debug.WriteLine("Main Form thread: " & AppDomain.GetCurrentThreadId)

  11:          Dim thread As Thread

  12:          thread = New Thread(AddressOf DoTask)

  13:          thread.IsBackground = True

  14:          thread.Start()

  15:      End Sub 

  16:   

  17:      Private Sub UpdateUI_handler(ByVal UpdateParameter As UIUpdateParameter)

  18:          Debug.WriteLine("Update progress bar thread: " & AppDomain.GetCurrentThreadId)

  19:          Dim theControlType As Object = Nothing

  20:          Dim theControl As Control = Nothing

  21:          For Each p As System.Reflection.PropertyInfo In Me.Controls(UpdateParameter.controlName).GetType().GetProperties()

  22:              theControl = Me.Controls(UpdateParameter.controlName)

  23:              theControlType = Convert.ChangeType(theControl, theControl.GetType)

  24:              If Not IsNothing(p.GetValue(theControlType, Nothing)) Then

  25:                  If UCase(p.Name.ToString) = UCase(UpdateParameter.PropertyName) Then

  26:                      p.SetValue(theControlType, Convert.ChangeType(UpdateParameter.value, p.PropertyType), Nothing)

  27:                  End If

  28:              End If

  29:          Next

  30:      End Sub

  31:      Private Sub DoTask(ByVal t)

  32:          For i As Integer = 1 To 10

  33:              Thread.Sleep(500)

  34:              Debug.WriteLine("Do Task thread: " & AppDomain.GetCurrentThreadId) 

  35:   

  36:              Dim uiUpdate2 As UpdateUI

  37:              uiUpdate2 = New UpdateUI(AddressOf UpdateUI_handler) 

  38:   

  39:              Dim UpdateParameter As New UIUpdateParameter

  40:              UpdateParameter.controlName = "ProgressBar1"

  41:              UpdateParameter.PropertyName = "value"

  42:              UpdateParameter.value = i

  43:              Me.Invoke(uiUpdate2, UpdateParameter) 

  44:   

  45:              UpdateParameter.controlName = "Label1"

  46:              UpdateParameter.PropertyName = "Text"

  47:              UpdateParameter.value = i

  48:              Me.Invoke(uiUpdate2, UpdateParameter) 

  49:   

  50:              UpdateParameter.controlName = "Textbox1"

  51:              UpdateParameter.PropertyName = "backcolor"

  52:              If i Mod 2 = 0 Then

  53:                  UpdateParameter.value = Color.Blue

  54:              Else

  55:                  UpdateParameter.value = Color.Yellow

  56:              End If 

  57:   

  58:              Me.Invoke(uiUpdate2, UpdateParameter)

  59:          Next i

  60:      End Sub

  61:  End Class 

  62:   

  63:  Public Class UIUpdateParameter

  64:      Public controlName As String

  65:      Public PropertyName As String

  66:      Public value As Object

  67:  End Class