Question

I’m trying to write a Console wrapper WPF gui that simply runs a selection of .bat files, I’d like to be able to view any output from the .bat files “live” (as if it were running in cmd).

I’ve looked into OutputDataReceived and event handlers which append text and then sent this to the screen, however it still waits until the Process has finished before anything appears on the screen.

How do I get the output from the .bat to appear in “real time”?

---

Snippits of my code so far (this is in a form):

The form has one button (go) and one multi-line text field (textArea).

private void go_Click(object sender, EventArgs e)
{
    ExecuteCommand();
}

public void ExecuteCommand()
{

    int ExitCode;
    ProcessStartInfo ProcessInfo;
    Process Process;

    //ProcessInfo = new ProcessStartInfo("cmd.exe", "/C z:\foo.bat");
    ProcessInfo = new ProcessStartInfo(@"z:\foo.bat"); ;

    ProcessInfo.CreateNoWindow = true;
    ProcessInfo.UseShellExecute = false;

    ProcessInfo.RedirectStandardError = true;
    ProcessInfo.RedirectStandardOutput = true;

    Process = new Process();
    Process.StartInfo = ProcessInfo;

    Process.OutputDataReceived += new DataReceivedEventHandler(OutputToTextArea);

    Process.Start();

    // Start the asynchronous read of the sort output stream.
    Process.BeginOutputReadLine();

    Process.WaitForExit();

    ExitCode = Process.ExitCode;
    Process.Close();
}

private int numOutputLines = 0;
private void OutputToTextArea(object sendingProcess, DataReceivedEventArgs outLine)
{
    // Collect the sort command output. 
    if (!String.IsNullOrEmpty(outLine.Data))
    {
        numOutputLines++;

        this.AppendToTextArea("[" + numOutputLines.ToString() + "] - " + outLine.Data + Environment.NewLine);
    }
}

private void AppendToTextArea(string s)
{
    if (this.textArea.InvokeRequired)
    {
        // It's on a different thread, so use Invoke.
        this.BeginInvoke (new MethodInvoker(() => textArea.AppendText(s)));
    } else {
        textArea.AppendText(s);
    }
}

Where my foo.bat is just a for loop:

ECHO OFF

FOR /L %%i IN (1,1,10) DO (
   echo %%i
   ping -n 2 127.0.0.1 >nul
)

Answer 1

Well yeah, you’re currently blocking the main thread (which is the UI thread) as you wait for process exit in ExecuteCommand, which is directly called from the UI thread (in go_Click).

Just start a new thread (or use a ThreadPool) (Winforms example):

private void button1_Click(object sender, EventArgs e)
{
    ThreadPool.QueueUserWorkItem(new WaitCallback(this.ExecuteCommand));
}

public void ExecuteCommand(object state)
{
    ...
}

If you’re using WPF, you probably want to use a BackgroundWorker.