Cross Threading in General

Cross Threading in General

• x3tje

  Now that you're looking into multithreading, I'd suggest you keep trying that, but if you want an 'ugly/easy' way to cross threads, then take a look at the pseudocode in my last reply of my first question on this forum:
  http://forums.microsoft.com/MSDN/ShowPost.aspx PostID=1109256&SiteID=1
  
  If you use a Timer in the sourceobject(xxLabel in the example) and make it synchronize with the targetobject(xxPanel in the example - the timer in the xxPanel is irrelevant), then you can access the targetobject in a threadsafe manner during the Timer's Tick/Elapsed event. And just to make sure that access to the target's thread is available, use an invokerequired/isHandleCreated condition like the pseudocode example in my last reply in that topic. I once read that a Timer's performancecost is extremely low, so don't worry about that aspect.
  
  Note that you're better off learning multithreading, though, but this is a little trick that can do the job if you're working on a small program that isn't affected by the possible "wait-for-the-sync" that occurs between the two objects.
  
  
  

• paruchuri

  You shouldn't need to. Concentrate on making the UpdateAttchmentList method thread safe using the techniques from the other thread and then anything calling it won't have to worry about it.

  I'd suggest its best practice to encapsulate the thread issues of the control and only worry about them in the procedure that interacts with it.

  What problem are you getting now ... maybe I can help

  Richard

  
  

• Denny B

  The WHOLE code Ok... you asked for it...

  [code=VB]

  Imports EngGraphicsTool.clsAttachmentGrid

  Imports EngGraphicsTool.clsAttachmentPackage

  Imports EngGraphicsTool.clsAttachmentPage

  Imports EngGraphicsTool.clsReferenceEvents

  Imports EngGraphicsTool.mdlConfiguration

  Imports System.Threading

  Public Class frmAttachmentTool

  Public WithEvents mainGrid As clsAttachmentGrid

  Public WithEvents RefEvtMgr As clsReferenceEvents

  Public txtBoxCollection As Collection

  Public chkBoxCollection As Collection

  Public cmdBtnCollection As Collection

  Private Delegate Sub fn1(Of T)(ByVal arg As T)

  Private Delegate Sub fn2(Of T, T1)(ByVal arg1 As T, ByVal arg2 As T1)

  Private Sub frmAttachmentTool_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

  MSConn()

  Try

  Dim txtBoxCol As New Collection, chkBoxCol As New Collection, cmdBtnCol As New Collection

  Dim newRefEventMgr As New clsReferenceEvents

  With txtBoxCol

  .Add(Me.txt_MainPage, "Main")

  .Add(Me.txt_NorthPage, "North")

  .Add(Me.txt_SouthPage, "South")

  .Add(Me.txt_EastPage, "East")

  .Add(Me.txt_WestPage, "West")

  .Add(Me.txt_NorthEastPage, "NorthEast")

  .Add(Me.txt_NorthWestPage, "NorthWest")

  .Add(Me.txt_SouthEastPage, "SouthEast")

  .Add(Me.txt_SouthWestPage, "SouthWest")

  End With

  With chkBoxCol

  .Add(Me.chk_Base, "Base")

  .Add(Me.chk_Addressing, "Addressing")

  .Add(Me.chk_Contours, "Contours")

  .Add(Me.chk_CreekPond, "CreekPond")

  .Add(Me.chk_OldCreekPond, "OldCreekPond")

  .Add(Me.chk_Orthophoto, "Orthophoto")

  .Add(Me.chk_Paving, "Paving")

  .Add(Me.chk_Storm, "Storm")

  .Add(Me.chk_Waste, "Waste")

  .Add(Me.chk_Water, "Water")

  End With

  With cmdBtnCol

  .Add(Me.btn_BaseLoader, "Base")

  .Add(Me.btn_AddressingLoader, "Addressing")

  .Add(Me.btn_ContoursLoader, "Contours")

  .Add(Me.btn_CreekPondLoader, "CreekPond")

  .Add(Me.btn_OldCreekPondLoader, "OldCreekPond")

  .Add(Me.btn_OrthophotoLoader, "Orthophoto")

  .Add(Me.btn_PavingLoader, "Paving")

  .Add(Me.btn_Stormloader, "Storm")

  .Add(Me.btn_WasteLoader, "Waste")

  .Add(Me.btn_WaterLoader, "Water")

  End With

  txtBoxCollection = txtBoxCol

  chkBoxCollection = chkBoxCol

  cmdBtnCollection = cmdBtnCol

  mainGrid = New clsAttachmentGrid

  If IsNumeric(Me.txt_MainPage.Text) Then

  mainGrid.SetGrid(CInt(txt_MainPage.Text))

  Else

  mainGrid.SetGrid(CInt(0))

  End If

  RefEvtMgr = newRefEventMgr

  MyMSApp.AddAttachmentEventsHandler(RefEvtMgr)

  MyMSApp.RasterManager.AddRasterEventsHandler(RefEvtMgr)

  UpdateAttachmentList()

  Catch ex As Exception

  End Try

  End Sub

  Private Sub mainGrid_GridLoaded() Handles mainGrid.GridLoaded

  Dim tmpTextBox As TextBox

  For Each tmpTextBox In txtBoxCollection

  tmpTextBox.Text = mainGrid.Package(tmpTextBox.Tag).PageNumber

  Next

  End Sub

  Private Sub CheckAllControls()

  ActivateAllCheckBoxes(mainGrid.ActivePackage)

  ActivateAllButtons(mainGrid.ActivePackage)

  End Sub

  Public Function ActivateTextBox(ByVal TargetTextBox As TextBox, ByVal Activate As Boolean) As TextBox

  Try

  Select Case Activate

  Case True

  Me.DeActivateAllTextBoxes()

  TargetTextBox.BackColor = Color.Yellow

  mainGrid.ActivatePackage_byName(CStr(TargetTextBox.Tag))

  CheckAllControls()

  Case False

  TargetTextBox.BackColor = Color.White

  DeActivateAllCheckBoxes()

  DeActivateAllButtons()

  End Select

  Return TargetTextBox

  Catch ex As Exception

  Dim newTextBox As New TextBox

  Return newTextBox

  End Try

  End Function

  Public Sub DeActivateAllTextBoxes()

  Dim tmpTxtBox As TextBox

  For Each tmpTxtBox In txtBoxCollection

  ActivateTextBox(tmpTxtBox, False)

  Next

  End Sub

  Public Function ActivateCheckBox(ByVal TargetAttachmentPage As clsAttachmentPage) As CheckBox

  Try

  Dim tmpCheckBox As CheckBox

  tmpCheckBox = Me.chkBoxCollection.Item(CStr(TargetAttachmentPage.Name))

  ' tmpCheckBox = Me.Controls.Item(CStr("chk_") + CStr(TargetAttachmentPage.Name))

  With tmpCheckBox

  .Checked = CBool(TargetAttachmentPage.CheckAttachStatus)

  End With

  Return tmpCheckBox

  Catch ex As Exception

  Dim newCheckBox As New CheckBox

  Return newCheckBox

  End Try

  End Function

  Public Sub ActivateAllCheckBoxes(ByVal TargetAttachmentPackage As clsAttachmentPackage)

  With TargetAttachmentPackage

  ActivateCheckBox(.Base())

  ActivateCheckBox(.Addressing())

  ActivateCheckBox(.Contours())

  ActivateCheckBox(.CreekPond())

  ActivateCheckBox(.OldCreekPond())

  ActivateCheckBox(.Orthophoto())

  ActivateCheckBox(.Paving())

  ActivateCheckBox(.Storm())

  ActivateCheckBox(.Waste())

  ActivateCheckBox(.Water())

  End With

  End Sub

  Public Sub DeActivateAllCheckBoxes()

  Dim tmpChkBox As CheckBox

  For Each tmpChkBox In chkBoxCollection

  With tmpChkBox

  .Checked = False

  End With

  Next

  End Sub

  Public Function ActivatePageButton(ByVal TargetAttachmentPage As clsAttachmentPage) As Button

  Try

  Dim tmpCmdBtn As Button

  tmpCmdBtn = Me.cmdBtnCollection.Item(CStr(TargetAttachmentPage.Name))

  ' tmpCmdBtn = Me.Controls.Item("btn_" + TargetAttachmentPage.Name + "Loader")

  With tmpCmdBtn

  Select Case TargetAttachmentPage.Exists

  Case True

  .Enabled = True

  Select Case TargetAttachmentPage.CheckAttachStatus

  Case True

  .Text = "Unload " + TargetAttachmentPage.Name

  .Tag = "LOADED"

  Case False

  .Text = "Load " + TargetAttachmentPage.Name

  .Tag = "UNLOADED"

  End Select

  Case False

  .Enabled = False

  .Text = "N/A"

  .Tag = "EMPTY"

  End Select

  End With

  Return tmpCmdBtn

  Catch ex As Exception

  Dim newCmdBtn As New Button

  Return newCmdBtn

  End Try

  End Function

  Public Sub ActivateAllButtons(ByVal TargetAttachmentPackage As clsAttachmentPackage)

  With TargetAttachmentPackage

  ActivatePageButton(.Base())

  ActivatePageButton(.Addressing())

  ActivatePageButton(.Contours())

  ActivatePageButton(.CreekPond())

  ActivatePageButton(.OldCreekPond())

  ActivatePageButton(.Orthophoto())

  ActivatePageButton(.Paving())

  ActivatePageButton(.Storm())

  ActivatePageButton(.Waste())

  ActivatePageButton(.Water())

  End With

  End Sub

  Public Sub DeActivateAllButtons()

  Dim tmpCmdBtn As Button

  For Each tmpCmdBtn In cmdBtnCollection

  With tmpCmdBtn

  .Text = "Loader"

  .Enabled = False

  End With

  Next

  End Sub

  Private Sub txt_MainPage_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_MainPage.TextChanged

  Dim tmpNewPageNumber As Integer

  Select Case Me.txt_MainPage.Text

  Case "", "X", "0"

  tmpNewPageNumber = 0

  Case Else

  tmpNewPageNumber = CInt(Me.txt_MainPage.Text)

  End Select

  mainGrid.SetGrid(tmpNewPageNumber)

  ActivateAllCheckBoxes(mainGrid.Package(CStr(Me.txt_MainPage.Tag)))

  ActivateAllButtons(mainGrid.Package(CStr(Me.txt_MainPage.Tag)))

  End Sub

  Private Sub txt_MainPage_Enter(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_MainPage.Enter

  ActivateTextBox(Me.txt_MainPage, True)

  End Sub

  Private Sub txt_NorthPage_Enter(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_NorthPage.Enter

  ActivateTextBox(Me.txt_NorthPage, True)

  End Sub

  Private Sub txt_SouthPage_Enter(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_SouthPage.Enter

  ActivateTextBox(Me.txt_SouthPage, True)

  End Sub

  Private Sub txt_EastPage_Enter(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_EastPage.Enter

  ActivateTextBox(Me.txt_EastPage, True)

  End Sub

  Private Sub txt_WestPage_Enter(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_WestPage.Enter

  ActivateTextBox(Me.txt_WestPage, True)

  End Sub

  Private Sub txt_NorthEastPage_Enter(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_NorthEastPage.Enter

  ActivateTextBox(Me.txt_NorthEastPage, True)

  End Sub

  Private Sub txt_NorthWestPage_Enter(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_NorthWestPage.Enter

  ActivateTextBox(Me.txt_NorthWestPage, True)

  End Sub

  Private Sub txt_SouthEastPage_Enter(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_SouthEastPage.Enter

  ActivateTextBox(Me.txt_SouthEastPage, True)

  End Sub

  Private Sub txt_SouthWestPage_Enter(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_SouthWestPage.Enter

  ActivateTextBox(Me.txt_SouthWestPage, True)

  End Sub

  Private Sub btn_BaseLoader_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_BaseLoader.Click

  Select Case Me.btn_BaseLoader.Tag

  Case "LOADED"

  mainGrid.ActivePackage.Base.DetachFile()

  Case "UNLOADED"

  mainGrid.ActivePackage.Base.AttachFile()

  Case "EMPTY"

  MsgBox("This button is temporarily out of order.", vbOKOnly, "Out Of Order")

  End Select

  CheckAllControls()

  End Sub

  Private Sub btn_CreekPondLoader_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_CreekPondLoader.Click

  Select Case Me.btn_CreekPondLoader.Tag

  Case "LOADED"

  mainGrid.ActivePackage.CreekPond.DetachFile()

  Case "UNLOADED"

  mainGrid.ActivePackage.CreekPond.AttachFile()

  Case "EMPTY"

  MsgBox("This button is temporarily out of order.", vbOKOnly, "Out Of Order")

  End Select

  CheckAllControls()

  End Sub

  Private Sub btn_OldCreekPondLoader_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_OldCreekPondLoader.Click

  Select Case Me.btn_OldCreekPondLoader.Tag

  Case "LOADED"

  mainGrid.ActivePackage.OldCreekPond.DetachFile()

  Case "UNLOADED"

  mainGrid.ActivePackage.OldCreekPond.AttachFile()

  Case "EMPTY"

  MsgBox("This button is temporarily out of order.", vbOKOnly, "Out Of Order")

  End Select

  CheckAllControls()

  End Sub

  Private Sub btn_ContoursLoader_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_ContoursLoader.Click

  Select Case Me.btn_ContoursLoader.Tag

  Case "LOADED"

  mainGrid.ActivePackage.Contours.DetachFile()

  Case "UNLOADED"

  mainGrid.ActivePackage.Contours.AttachFile()

  Case "EMPTY"

  MsgBox("This button is temporarily out of order.", vbOKOnly, "Out Of Order")

  End Select

  CheckAllControls()

  End Sub

  Private Sub btn_WaterLoader_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_WaterLoader.Click

  Select Case Me.btn_WaterLoader.Tag

  Case "LOADED"

  mainGrid.ActivePackage.Water.DetachFile()

  Case "UNLOADED"

  mainGrid.ActivePackage.Water.AttachFile()

  Case "EMPTY"

  MsgBox("This button is temporarily out of order.", vbOKOnly, "Out Of Order")

  End Select

  CheckAllControls()

  End Sub

  Private Sub btn_WasteLoader_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_WasteLoader.Click

  Select Case Me.btn_WasteLoader.Tag

  Case "LOADED"

  mainGrid.ActivePackage.Waste.DetachFile()

  Case "UNLOADED"

  mainGrid.ActivePackage.Waste.AttachFile()

  Case "EMPTY"

  MsgBox("This button is temporarily out of order.", vbOKOnly, "Out Of Order")

  End Select

  CheckAllControls()

  End Sub

  Private Sub btn_StormLoader_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_Stormloader.Click

  Select Case Me.btn_Stormloader.Tag

  Case "LOADED"

  mainGrid.ActivePackage.Storm.DetachFile()

  Case "UNLOADED"

  mainGrid.ActivePackage.Storm.AttachFile()

  Case "EMPTY"

  MsgBox("This button is temporarily out of order.", vbOKOnly, "Out Of Order")

  End Select

  CheckAllControls()

  End Sub

  Private Sub btn_PavingLoader_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_PavingLoader.Click

  Select Case Me.btn_PavingLoader.Tag

  Case "LOADED"

  mainGrid.ActivePackage.Paving.DetachFile()

  Case "UNLOADED"

  mainGrid.ActivePackage.Paving.AttachFile()

  Case "EMPTY"

  MsgBox("This button is temporarily out of order.", vbOKOnly, "Out Of Order")

  End Select

  CheckAllControls()

  End Sub

  Private Sub btn_OrthophotoLoader_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_OrthophotoLoader.Click

  Select Case Me.btn_OrthophotoLoader.Tag

  Case "LOADED"

  mainGrid.ActivePackage.Orthophoto.DetachFile()

  Case "UNLOADED"

  mainGrid.ActivePackage.Orthophoto.AttachFile()

  Case "EMPTY"

  MsgBox("This button is temporarily out of order.", vbOKOnly, "Out Of Order")

  End Select

  CheckAllControls()

  End Sub

  Private Sub btn_AddressingLoader_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_AddressingLoader.Click

  Select Case Me.btn_AddressingLoader.Tag

  Case "LOADED"

  mainGrid.ActivePackage.Addressing.DetachFile()

  Case "UNLOADED"

  mainGrid.ActivePackage.Addressing.AttachFile()

  Case "EMPTY"

  MsgBox("This button is temporarily out of order.", vbOKOnly, "Out Of Order")

  End Select

  CheckAllControls()

  End Sub

  Private Sub txt_NorthPage_DoubleClick(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_NorthPage.DoubleClick

  With txt_MainPage

  .Focus()

  .Text = txt_NorthPage.Text

  End With

  End Sub

  Private Sub txt_SouthPage_DoubleClick(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_SouthPage.DoubleClick

  With txt_MainPage

  .Focus()

  .Text = txt_SouthPage.Text

  End With

  End Sub

  Private Sub txt_EastPage_DoubleClick(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_EastPage.DoubleClick

  With txt_MainPage

  .Focus()

  .Text = txt_EastPage.Text

  End With

  End Sub

  Private Sub txt_WestPage_DoubleClick(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_WestPage.DoubleClick

  With txt_MainPage

  .Focus()

  .Text = txt_WestPage.Text

  End With

  End Sub

  Private Sub txt_NorthEastPage_DoubleClick(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_NorthEastPage.DoubleClick

  With txt_MainPage

  .Focus()

  .Text = txt_NorthEastPage.Text

  End With

  End Sub

  Private Sub txt_NorthWestPage_DoubleClick(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_NorthWestPage.DoubleClick

  With txt_MainPage

  .Focus()

  .Text = txt_NorthWestPage.Text

  End With

  End Sub

  Private Sub txt_SouthWestPage_DoubleClick(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_SouthWestPage.DoubleClick

  With txt_MainPage

  .Focus()

  .Text = txt_SouthWestPage.Text

  End With

  End Sub

  Private Sub txt_SouthEastPage_DoubleClick(ByVal sender As Object, ByVal e As System.EventArgs) Handles txt_SouthEastPage.DoubleClick

  With txt_MainPage

  .Focus()

  .Text = txt_SouthEastPage.Text

  End With

  End Sub

  Private Sub btn_AssignActive_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_AssignActive.Click

  With txt_MainPage

  .Focus()

  .Text = GetActivePageNumber()

  End With

  End Sub

  Private Sub btn_ClearPage_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_ClearPage.Click

  ClearAllAttachments()

  With txt_MainPage

  .Focus()

  .Text = GetActivePageNumber()

  End With

  UpdateAllViews()

  End Sub

  Private Sub RefEvtMgr_AttachmentStatus1(ByVal TheAttachment As MicroStationDGN.Attachment, ByVal Attached As Boolean) Handles RefEvtMgr.AttachmentStatus

  UpdateAttachmentList(CStr(TheAttachment.LogicalName), Attached)

  End Sub

  Public Sub UpdateAttachmentList(Optional ByVal TargetLogicalName As String = "BLANK", Optional ByVal LeaveThis As Boolean = True)

  Try

  Dim MyCmb As System.Windows.Forms.ComboBox

  Dim counter As Integer, EntryText As String

  Dim PageType As String, PageNumber As Integer, NumberOfAttachments As Integer

  Dim MyActiveModel As ModelReference, MyAttachments As Attachments, MyAttachment As Attachment

  MyActiveModel = MyAMR

  MyAttachments = MyActiveModel.Attachments

  MyCmb = Me.cmb_References

  clearCombobox(MyCmb)

  NumberOfAttachments = IIf((LeaveThis = True), MyAttachments.Count, MyAttachments.Count - 1)

  For counter = 0 To NumberOfAttachments - 1

  MyAttachment = MyAttachments.Item(counter + 1)

  PageType = LogicalName_to_PageType(MyAttachment.LogicalName)

  PageNumber = LogicalName_to_PageNumber(MyAttachment.LogicalName)

  EntryText = PageType + " Type, Page #: " + CStr(PageNumber)

  ' MyCmb.Items.Add(EntryText)

  addComboBoxItem(MyCmb, EntryText)

  Next counter

  Catch ex As Exception

  Select Case Err.Number

  Case 5 ' Cross-thread operation not valid: Control 'cmb_References' accessed from a thread other than the thread it was created on.

  End Select

  End Try

  End Sub

  Private Shared Sub clearCombobox(ByVal MyComboBox As ComboBox)

  If MyComboBox.InvokeRequired Then

  MyComboBox.Invoke(New fn1(Of ComboBox)(AddressOf clearCombobox), MyComboBox)

  Else

  MyComboBox.Items.Clear()

  End If

  End Sub

  Private Shared Sub addComboBoxItem(ByVal MyComboBox As ComboBox, ByVal ItemEntry As String)

  If MyComboBox.InvokeRequired Then

  MyComboBox.Invoke(New fn2(Of ComboBox, String)(AddressOf addComboBoxItem), MyComboBox, ItemEntry)

  Else

  MyComboBox.Items.Add(ItemEntry)

  End If

  End Sub

  Protected Overrides Sub Finalize()

  MyMSApp.RemoveAttachmentEventsHandler(RefEvtMgr)

  MyMSApp.RasterManager.RemoveRasterEventsHandler(RefEvtMgr)

  MyBase.Finalize()

  End Sub

  End Class

  [/code]

  Again, I am getting the errors whenever the RefEvtMgr event fires off UpdateAttachmentList...

  
  
  

• Fredrik Melin

  Richard,

  I am so glad I caught you online... I think my original problem, with updating the combobox, is being caused by an internal Sub.

  I'm hoping you can tell me what to do.

  I use a Sub called UpdateAttachmentList to get a list of attached reference files in my working Microstation Application and update that list to my combobox.

  I just noticed that UpdateAttachmentList is called from a Microstation Event...

  [code=vb]

  Private Sub RefEvtMgr_AttachmentStatus1(ByVal TheAttachment As MicroStationDGN.Attachment, ByVal Attached As Boolean) Handles RefEvtMgr.AttachmentStatus

  UpdateAttachmentList(CStr(TheAttachment.LogicalName), Attached)

  End Sub

  [/code]

  So I wonder if there is a way to make sure that UpdateAttachmentList when called from THERE is threaded appropriately

  
  
  

• Socrates Kapetaneas

  The problem I am getting now is that whenever it hits that ComboBox from a InvokeRequired = True event It just freezes

  My biggest problem with all of this is that I had this WHOLE thing working JUST FINE in VBA...

  However VBA has a Max Controls limit. So as I attempted to make my little tool / app larger I hit a point where it stopped allowing me to add new controls to it... SO, I am converting this thing over to .NET and now I am hitting the Thread Issues.

  
  
  

• Bealby

  If you make your application multithreaded then you will have to deal with threading issues. If you want it to be single threader, then don't create threads. The application will respond more in-line to what you are used to.

  Threads don't magically create themselves (depends on what components you are using...) - what is it that's causing this cross thread issue

  
  
  

• ctssoms

  MyComboBox.Invoke(New fn1(Of ComboBox)(AddressOf clearCombobox), MyComboBox)

  That line hangs...

  Sell Ha... My code is a little wasteful, especially with all the new stuff I am learning... chuckle. I just wish I had dealt with threading before. I am 100% self-taught, so every new thing is such a hurdle. Thankfully, I have this board and people like yourself who are willing to help out us newbs.

  
  
  

• Kamii47

  ... is this code I can sell

  Can you advise which line causes the debugger to hang

  
  

• Hrishikesh

  I did not purposely create a thread... having never worked with them up till now I was happy to continue on my path until I have a chance for some more courses on programming... that said...

  I am building a VB.NET Application to use with Bentley's Microstation v8

  Whenever you attach a reference to an active DGN file, it fires off an event. I want that event to insert the name and id of the reference that was attached.

  Well, THAT event is what is calling my UpdateAttachmentList Sub, and THAT is when I have problems. I also call the UpdateAttachmentList Sub when the Form is first Loaded. That way any references ALREADY attached are added into my ComboBox then as well.

  Like I said. I DO have UpdateAttachmentList called from other locations. BUT it is only hitting problems when called from the

  [code=vb]

  Public WithEvents RefEvtMgr As clsReferenceEvents

  ...

  Private Sub RefEvtMgr_AttachmentStatus1(ByVal TheAttachment As MicroStationDGN.Attachment, ByVal Attached As Boolean) Handles RefEvtMgr.AttachmentStatus

  UpdateAttachmentList(CStr(TheAttachment.LogicalName), Attached)

  End Sub

  [/code]

  SO, again... I am NOT using threads on purpose.

  
  
  

• shakalama

  Help
  
  

• Hiral

  Hanging:

  Me.cmb_References.Invoke(New MethodInvoker(AddressOf ClearCombobox))

  Help me Mr. Popeil... I'm in trouble. I guess this means I need to research and start learning Threads I am assuming that my 'thread' problem is arising because I am working with the Bentley Microstation. I believe there is serious threading done in it, it is a CADD program. Thanks for your time again...

  
  
  

• Sang Hoang

  Hi

  I never used VBA but I suspect that it's used the single thread apartment model, the same way that VB6 application did.

  VB.NET opened up the possibility of developing multi-threaded applications in your favourite language.

  With regard to the control classes, these are just simple wrappers for the Win32 equivalent which also use an STA model. The Win32 controls use a message dispatcher that runs on a single thread (the one that was running when it was created). These controls are not therefore inherently thread safe.

  The .NET wrapper gives us an easy way to ensure that communication with the underlying control is on the same thread on which the control was created (assuming we need to worry about such things .. which most folk don't); the Invoke and InvokeRequired methods. Invoke simply ensures the passed delegate is executed on the controls thread thus allowing you to safely interact with it.

  Indeed I would agree that the .net developers could perhaps have solved this problem by invoking internal delegates, but I'd also suggest that there was little reason to saddle controls and control developers with the overhead where it (most of the time) is unneccessary. In short, it probably helps keep things simpler and speedier for most VB developers .. which is after all the ultimate goal of the language.

  Richard

  
  

• Salte1

  He he .. it's like being a real programmer .. once you grasp it, you'll never look back (maybe).

  What do you mean by 'freezing' What is Your whole app or something else

  If you post your current code, I'll have a look.

  Richard

  
  

• Lenmax

  randomblink wrote:

  MyComboBox.Invoke(New fn1(Of ComboBox)(AddressOf clearCombobox), MyComboBox) That line hangs... Sell Ha... My code is a little wasteful, especially with all the new stuff I am learning... chuckle. I just wish I had dealt with threading before. I am 100% self-taught, so every new thing is such a hurdle. Thankfully, I have this board and people like yourself who are willing to help out us newbs.

   

  Now I've seen how the UpdateWotsit function sits with the other code, I wouldn't pass the combobox as a parameter to your clear and update methods.  Instead change them to ....

  Private Sub ClearCombobox()

  If Me.cmb_References.InvokeRequired Then

  Me.cmb_References.Invoke(New MethodInvoker(AddressOf ClearCombobox))

  Else

  Me.cmb_References.Items.Clear()

  End If

  End Sub

  Private Sub addComboBoxItem(ByVal ItemEntry As String)

  If Me.cmb_References.InvokeRequired Then

  Me.cmb_References.Invoke(New fn1(Of String)(AddressOf addComboBoxItem), ItemEntry)

  Else

  Me.cmb_References.Items.Add(ItemEntry)

  End If

  Let me know how you get on.

  Richard

  
  
• Cross Threading in General