Problem with with output redirection of a process

Question

User-1522632901 posted

Hi!

Maybe you peeps can help me. I am doing a program that runs diverse powershell scripts from the interface...

It works!     once.

Every time I try and start another script, VB throws me an "invalidOperationException" saying that "An async read operation has already been started on the stream".

I do not get it, as I do close the process after all is done to redo it anew. What am I missing?

Here is the code that calls the script

Public Sub RunScript(Script As String, Param1 As String, Param2 As String)

        myProcess.StartInfo.FileName = "powershell"
        myProcess.StartInfo.Arguments =  
        myProcess.StartInfo.UseShellExecute = False
        myProcess.StartInfo.CreateNoWindow = True
        myProcess.StartInfo.RedirectStandardInput = False
        myProcess.StartInfo.RedirectStandardOutput = True
        myProcess.StartInfo.RedirectStandardError = False
        myProcess.StartInfo.StandardOutputEncoding = System.Text.Encoding.GetEncoding(Globalization.CultureInfo.CurrentCulture.TextInfo.OEMCodePage)
        myProcess.EnableRaisingEvents = True

        Application.DoEvents()
   
        AddHandler myProcess.OutputDataReceived, AddressOf proc_OutputDataReceived

        myProcess.Start()
        myProcess.BeginOutputReadLine()
        myProcess.Close()
    End Sub

I had to remove my arguments, as the line was screwing the code renderer here...

The error pops on the "myProcess.BeginOutputReadLine()" line.

Thanks for the help!

Answer 1

User2053451246 posted

Application.DoEvents()

AddHandler myProcess.OutputDataReceived, AddressOf proc_OutputDataReceived

What is going on in these events?  Any stream reading/writing?  Or anything else that would help us figure out where the problem is?  If you comment out those lines and test do you have the same problem?

Answer 2

User-1522632901 posted

Hi!

Thanks for the reply. The DoEvents was pasted from the code I found.  it passes control from the application to the operating system.  It helps in updating in real time, without dabling in threaded porcesses.

the AddHandler line is for redirecting the powershell ofput to a text box. Here is the code:

    Public Sub proc_OutputDataReceived(ByVal sender As Object, ByVal e As DataReceivedEventArgs)
        If Me.InvokeRequired = True Then
            Me.Invoke(myDelegate, e.Data)
        Else
            UpdateTextBox(e.Data)

        End If
    End Sub

It is necessary.

But I did try and remove the do events and lo and behold, it works now!

So mark this as solved and a big thanks. I will be more wary of that function from now on...