.NET Framwork Passing information to already running process

Question

I currently have an application (.Net Frameowork) that gets triggered via CMD request. I would like to only have one instance of the application running and I would like to handle the arguments being passed in. Right now I have the application identifying if there is a currently running instance.

Example:

1. cmd ReceiptApplication.exe -r:blah -c:foo
2. cmd ReceiptApplication.exe -r:blah2 -c:foo2

The second request would pass blah2 and foo2 to the currently running process of ReceiptApplication.exe and kill the second application.

What is the process or pattern for passing the parameters?

using System.Linq;
using System.Windows;

namespace ReceiptApplication
{
/// <summary>
/// Interaction logic for App.xaml
/// </summary>
public partial class App : Application
{
    /// <summary>
    /// Startup the application, 
    /// Process:
    ///     Get the arguments passed in
    ///     Validate the arguments
    ///     check to see if there is a running instance of the application
    ///     if there is a running app
    ///         Pass the arguments to the running application
    ///         kill the current application. 
    ///     else
    ///         process the request
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    private void Application_Startup(object sender, StartupEventArgs e)
    {
        string receiptID = GetArgument(e.Args, "-r");
        string creditUnionFile = GetArgument(e.Args, "-c");
        if(receiptID == null || creditUnionFile == null)
        {
            System.Windows.Forms.Application.Exit();
        }
        if (AppCurrntlyRunning())
        {
            //pass arguments to the current running application
            Process alreadyRunningApplication = GetOriginalProcess();
            var streamWriter = alreadyRunningApplication.StandardInput;
            streamWriter.WriteLine("-r:blah -c:yay");

            //kill this one
            System.Windows.Forms.Application.Exit();
        }
        MessageBox.Show("Starting UI!");
        MainWindow wnd = new MainWindow();
        wnd.PullReceipt(receiptID, creditUnionFile);
        wnd.Show();
    }
}
}

Answer 1

If you want to pass information to your application during runtime you could use the standard input stream. This is how it's done: How to write to stdin in C# Then in your running application you can read the written data with Console.ReadLine();

On the linked answer on how to write to stdin in C# mind that instead of starting a new application you want to store a reference to your already running one:

//DON'T do this
//var process = new Process();
//process.StartInfo = startInfo;
//process.Start();
        
//DO this
var processes =  Process[] localByName = Process.GetProcessesByName("The Title Of My Application"); //This should give back multiple processes if you start your application for a second time so be mindful about that
Process alreadyRunningApplication;
if(processes.Length > 1)
{
    if (processes[0].Id == Process.GetCurrentProcess.Id)
    {
        alreadyRunningApplication = processes[1];
    }
    else
    {
        alreadyRunningApplication = processes[0];
    }
    var streamWriter = alreadyRunningApplication.StandardInput;
    streamWriter.WriteLine("I'm supplying input!");
}
else
{
//If we get into this else, it means this instance is the first running instance so your normal program behavior should go here for example using Console.ReadLine();
}