C# - Launch Invisible Process (CreateNoWindow & WindowStyle not working?)

Question

I have 2 programs (.exe) which I've created in .NET. We'll call them the Master and the Worker. The Master starts 1 or more Workers. The Worker will not be interacted with by the user, but it is a WinForms app that receives commands and runs WinForms components based on the commands it receives from the Master.

I want the Worker app to run completely hidden (except showing up in the Task Manager of course). I thought that I could accomplish this with the StartInfo.CreateNoWindow and StartInfo.WindowStyle properties, but I still see the Client.exe window and components in the form. However, it doesn't show up in the taskbar.

   Process process = new Process
      {
          EnableRaisingEvents = true,
          StartInfo =
              {
                  CreateNoWindow = true,
                  WindowStyle = ProcessWindowStyle.Hidden,
                  FileName = "Client.exe",
                  UseShellExecute = false,
                  ErrorDialog = false,
              }
      };

What do I need to do to let Client.exe run, but not show up?ㅤㅤㅤㅤㅤ

Answer 1

Your usage of CreateNoWindow/WindowStyle works fine on my system with notepad.exe (e.g. it is hidden but running in the background), so it's probably something the WinForms app is doing. Some ideas:

Option 1: If you control the WinForms worker process, you can override Control.SetVisibleCore to always hide the form. If you don't want to always hide it, you can pass a command-line argument to it, e.g. /hide that will cause it to be hidden. Example (assuming there's already code-behind for the form):

public partial class MyForm : Form
{
    public MyForm()
    {
        InitializeComponent();
    }

    protected override void SetVisibleCore(bool value)
    {
        // You'd probably want to parse the command line.
        if (Environment.CommandLine.Contains("/hide"))
            base.SetVisibleCore(false);
        else
            base.SetVisibleCore(value);
    }
}

With this, running MyForm.exe results in a process with a visible form. Running MyForm.exe /hide results in a process with a hidden form. You could pass the /hide argument from your master process, so then normal users running the application will still see it.

Option 2: You can hide the application after it starts by doing a P/Invoke to ShowWindow. More info on this here. This has the drawback that you can sometimes see the worker window flicker into existence before being hidden. Example:

class Program
{
    public static void Main(string[] args)
    {
        ProcessStartInfo psi = new ProcessStartInfo()
        {
            FileName = @"C:\windows\system32\notepad.exe",
        };

        Process process = Process.Start(psi);

        // Wait until the process has a main window handle.
        while (process.MainWindowHandle == IntPtr.Zero)
        {
            process.Refresh();
        }

        ShowWindow(process.MainWindowHandle, SW_HIDE);
    }

    const int SW_HIDE = 0;

    [DllImport("user32.dll")]
    static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);
}