How to access objects from another thread...

How to access objects from another thread...

• jack katz

  I'll post the code i use.

  In my global vars:

  Delegate Sub UpdateLogDelegate(ByVal toAdd As String, ByVal newLIne As Boolean, ByVal color As Color)
  Dim updateLogDel As UpdateLogDelegate = New UpdateLogDelegate(AddressOf UpdateLog)

  I have a function that traps all gui updates from another thread(it doesn't matter what control you call invoke on as long as it is on the main form):

  Public Sub UpdateGuiFromThread(ByVal method As String, ByVal msg As String, _
  ByVal boolValue As Boolean, ByVal color As Drawing.Color)

  'if form is not currently in closing sequence, update the GUI
  If inExit = False Then

  Select Case method
  Case "updateSendButtonDel"
  Me.btn_asynch_upload.Invoke(updateSendButtonDel, boolValue)
  Case "updateServerDel"
  Me.txt_server_name.Invoke(updateServerDel, msg)
  Case "updateLogDel"
  Me.txt_log.Invoke(updateLogDel, msg, boolValue, color)
  Case "updateFileDel"
  Me.txt_server_name.Invoke(updateFileDel, msg)
  Case "updateStatusDel"
  Me.txt_server_name.Invoke(updateStatusDel, msg)
  Case "refreshGuiDel"
  Me.txt_server_name.Invoke(refreshGuiDel)
  Case "updateProgressBarDel"
  Me.txt_server_name.Invoke(updateProgressBarDel, CInt(msg))
  Case "updateTrayIconDel"
  Me.txt_server_name.Invoke(updateTrayIconDel, msg)
  End Select
  End If
  End Sub

  Then the updateLog function:

  Private Sub UpdateLog(ByVal toAdd As String, ByVal newLine As Boolean, ByVal color As Drawing.Color)
  Me.txt_log.SelectionColor = color
  Me.txt_log.SelectedText = toAdd
  'Me.txt_log.AppendText(toAdd)
  If newLine = True Then
  Me.txt_log.AppendText(Environment.NewLine)
  End If
  ScrollToBottom()
  End Sub

  Then the call from another thread:

  UpdateGuiFromThread("updateLogDel", "Sending file " + fileToUpload.ToString, True, NormColor)

  This is not the most elegant code but it works for me.

  Good Luck,

  Lushdog
  

  
  

• Kartik Subramani

  Thank you shakalama, that actually did the trick. Where I went wrong is in how i called Invoke. I was calling d.invoke so switching that to me.invoke worked out perfectly.
  
  
  

• abhig

  Interesting, i tried shaka's technique a few month's ago and it didn't work for me. I'll try it out again, it would cut down alot on that garbage i posted above :)

  lushdog

  
  

• mr.flx

  Ok, i tried that using an example i found online and it still is giving the same error.
  
  Here's the code that I currently have:
  
  Imports System
  Imports System.Threading
  Imports System.Net
  Imports System.Net.Sockets
  
  Public Class Form1
  Protected Delegate Sub mydelsub(ByVal msg As String)
  
  Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
  Dim sock As System.Net.Sockets.Socket
  sock = New System.Net.Sockets.Socket(Net.Sockets.AddressFamily.InterNetwork, Net.Sockets.SocketType.Stream, Net.Sockets.ProtocolType.Tcp)
  sock.Connect(New IPEndPoint(IPAddress.Parse("127.0.0.1"), 80))
  
  
  Dim request As String = "GET / HTTP/1.1" + Environment.NewLine
  request = request + "host: http://joelclipperton.us" + Environment.NewLine
  request = request + "connection: close" + Environment.NewLine + Environment.NewLine
  
  
  Dim buffer As Byte() = System.Text.Encoding.ASCII.GetBytes(request)
  
  Dim state As AsyncState = New AsyncState
  state.sock = sock
  state.buffer = buffer
  
  sock.BeginSend(buffer, 0, buffer.Length, SocketFlags.None, New AsyncCallback(AddressOf SendCallback), state)
  End Sub
  
  
  Public Sub ReceiveCallback(ByVal ar As IAsyncResult)
  Dim del As mydelsub
  del = New mydelsub(AddressOf printtobox)
  
  Try
  Dim state As AsyncState = CType(ar.AsyncState, AsyncState)
  Dim count As Integer = state.sock.EndReceive(ar)
  
  If (count > 0) Then
  del.Invoke(System.Text.Encoding.ASCII.GetString(state.buffer, 0, count))
  state.sock.BeginReceive(state.buffer, 0, state.buffer.Length, SocketFlags.None, New AsyncCallback(AddressOf ReceiveCallback), state)
  Else
  del.Invoke(Environment.NewLine + "DONE: Socket was closed by the remote peer")
  End If
  
  Catch ex As Exception
  del = New mydelsub(AddressOf showerror)
  del.Invoke(ex.ToString)
  End Try
  End Sub
  
  Public Sub SendCallback(ByVal ar As IAsyncResult)
  Dim del As mydelsub
  del = New mydelsub(AddressOf printtobox)
  Try
  Dim state As AsyncState = CType(ar.AsyncState, AsyncState)
  state.sock.EndSend(ar)
  
  del.Invoke("Data Sent...")
  del.Invoke("Waiting to receive data")
  del.Invoke("")
  
  state.sock.BeginReceive(state.buffer, 0, state.buffer.Length, SocketFlags.None, New AsyncCallback(AddressOf ReceiveCallback), state)
  Catch ex As Exception
  del = New mydelsub(AddressOf showerror)
  del.Invoke(ex.ToString)
  End Try
  End Sub
  
  Protected Sub showerror(ByVal msg As String)
  MessageBox.Show(msg)
  End Sub
  
  Protected Sub printtobox(ByVal msg As String)
  Textbox1.AppendText(msg)
  End Sub
  End Class
  
  
  Public Class AsyncState
  Public sock As Socket
  Public buffer As Byte()
  End Class
  
  I know the code works because I can send the output of the receive buffer to a message box and it works just fine. Upon executing I get a System.InvalidOperationException: Corsss-thread operation not valid: Control 'Textbox1' accessed from a thread other than the thread it was created on.
  
  So using a delegate I'm still getting the same error. Is there something wrong with how i've implemented delegates
  
  
  

• al kerr

  Anyone have any ideas
  
  
  

• Mike Cating

  Look up delegates and .invoke in the MSDN. Basically you call a delegate that will marshal your function and makes sure that the update to the gui (.appendText) is done on the GUI thread.
  
  I'd write the code out for you but my eyes are burning right now.
  
  lushdog
  
  

• SpiderX81

  hi,

  the short and best way is this to creat a delegate for a method that take string, and then creat a method that check if the invokerequired if its required it call the delegate and you reference this method in your code not the textbox, this code is not tested but you got the idea

  Delegate Sub settxtconn(ByVal text As String)
  
  Sub SetTxtConnStatus(ByVal txt As String)
   If Me.txtConnStatus.InvokeRequired Then
     Dim d As settxtconn = AddressOf SetTxtConnStatus
     Me.Invoke(d, New Object() {txt})
   Else
     Me.txtConnStatus.Text = txt
   End If
  End Sub

  hope this helps

   

  
  
  
• How to access objects from another thread...