Log In

Come Join Us!

Are you a
Computer / IT professional?
Join Tek-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Tek-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Process delegate updates textbox.text but the textbox does not repaint until process finished

Process delegate updates textbox.text but the textbox does not repaint until process finished

Process delegate updates textbox.text but the textbox does not repaint until process finished

There are many similar problems on the internet but none have solved this exact problem.
I use a process and delegate to call a c program and redirect output to a textbox.
I want the textbox to update line by line, in real time. BUT it seems to wait until a large chunk of text is in the textbox.text property before repainting it.

CODE --> vb.net

Private Sub cmdReadFields_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles cmdReadFields.Click
        txtOutput.AppendText(vbCrLf & "Reading Fields from " & gstrSimulatorType & vbCrLf)
        mProcess = New Process

        AddHandler mProcess.OutputDataReceived, AddressOf process_OutputDataReceived
        AddHandler mProcess.ErrorDataReceived, AddressOf process_OutputDataReceived
        ' handlers should send both output and errors to same handling sub

        ' now can call the c program in a process (separate thread) and redirect the output to the textbox
        Dim startInfo As New ProcessStartInfo
        startInfo.FileName = Path.Combine(System.AppDomain.CurrentDomain.BaseDirectory(), "ReadFields\ReadFieldsInfo.exe")
        startInfo.WorkingDirectory = Path.Combine(System.AppDomain.CurrentDomain.BaseDirectory(), "ReadFields")
        startInfo.UseShellExecute = False
        startInfo.CreateNoWindow = True
        'startInfo.RedirectStandardInput = True    'doesn't seem to help, so commented out
        startInfo.RedirectStandardOutput = True
        startInfo.RedirectStandardError = True
        startInfo.ErrorDialog = True
        mProcess.StartInfo = startInfo
        mProcess.EnableRaisingEvents = True


        Catch ex As Exception
            MsgBox("error" & ex.Message)

            mProcess.Close()  ' tried commenting this out - no change
            mProcess.Dispose()  ' tried commenting this out - no change
        End Try

     End Sub
    ' fires from handler, when output data rcvd from process 
    Public Sub process_OutputDataReceived(ByVal sender As Object, ByVal e As DataReceivedEventArgs)
        ' called as the handler for data output being detected in the redirect
    End Sub

    Delegate Sub UpdateTxtBoxDelegate(ByVal Text As String)

    Public Sub UpdateTextBox(ByVal Tex As String)
        If txtOutput.InvokeRequired Then
            Dim myDelegate As New UpdateTxtBoxDelegate(AddressOf UpdateTextBox)
            Dim args As Object() = {Tex}
            Me.txtOutput.Invoke(myDelegate, args)
            txtOutput.AppendText(Tex & Environment.NewLine)
            ' application.doEvents   ' tried this but only refreshes GUI when stepping through code with F11
        End If
    End Sub 

Note 1: I found none of the delegate calls run until the main sub cmdReadFields_Click() finishes and exits;
THEN all the calls to the delegate are executed and the text box prints out all the text at the end.
Interesting- I thought a separate thread would be running these delegate events while the GUI command button event is still running.

Note 2: I tried a breakpoint in the UpdateTextBox() sub and I watched the value of txtOutput.text.
The text property was actually updating at each call but the GUI textbox did NOT update/refresh until it was 'nearly all done'.

When the c program runs in a console it prints to screen a line-by-line report of what the code is doing as it creates a copy of a dll,
creates an object in memory and reads data fields from that object then destroys the object and dll copy.
( The c program prints a line feed after each line and flushes the buffer )

HOWEVER, WHEN the c program runs in the vb.net thread (process), the textbox shows nothing while the console program is gradually printing out the
creation messages, reading data values etc. then the textbox suddenly updates to show the entire block of text lines; Then it again pauses while the
c program is destroying the objects and printing out strings about this; THEN the textbox suddenly prints those lines out.

Note 3: I tried application.doEvents, as many internet posts suggest, but that does not refresh the textbox in real time either.
In fact... when I put a breakpoint in the UpdateTextBox() sub and let it run one call at a time, the GUI actually DID update the textbox at each line BUT when I
run the code without the breakpoint, the textbox does NOT update for each line.
I can only assume the successful update when stepping through the code is because the IDE is passing focus between the GUI and code as I step through,
whereas in continuous run mode the textbox never receives a paint message.(?)

Note 4: I also tried using an exit event for the process at one time and I had tried commenting out the mProcess.close and mProcess.dispose statements
inside the main sub in case I was somehow destroying the process before my exit event was called but that did not help anything.

***** SO.. Has anyone already solved this?
How do I get the textbox to actually repaint at each update of the .text property so my lines are printed out one at a time, in real time, as the c program is doing behind the scenes???

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Tek-Tips Forums free from inappropriate posts.
The Tek-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Tek-Tips forums is a member-only feature.

Click Here to join Tek-Tips and talk with other members!

Close Box

Join Tek-Tips® Today!

Join your peers on the Internet's largest technical computer professional community.
It's easy to join and it's free.

Here's Why Members Love Tek-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close