Quick XML Reader

using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;
using Trezorix.Qxr.Forms;
using System.IO;
using System.Diagnostics;
using System.Runtime.InteropServices;

namespace Trezorix.Qxr
{
	static class Program
	{

		// Extern DLL for sending a message to the running software instance
		[DllImport("User32.dll", EntryPoint = "SendMessage")]
		public static extern int SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, ref COPYDATASTRUCT lParam);

		// Extern DLL for setting the focus on the running software
		[DllImport("user32.dll")]
		[return: MarshalAs(UnmanagedType.Bool)]
		static extern bool SetForegroundWindow(IntPtr hWnd);

		// Constant for sending data between software instances
		internal const int WM_COPYDATA = 0x4A;

		// Structure containing data sent to other software instances
		public struct COPYDATASTRUCT
		{
			public IntPtr dwData;
			public int cbData;
			[MarshalAs(UnmanagedType.LPStr)]
			public string lpData;
		}

		/// <summary>
		/// The main entry point for the application.
		/// </summary>
		[STAThread]
		static void Main(string[] arguments)
		{

			string m_sFileToOpen = null;

			foreach (string fileToOpen in arguments)
			{
				if (File.Exists(fileToOpen))
					m_sFileToOpen = fileToOpen;
			}


			// Get the running instances of the system
			Process proc = Process.GetCurrentProcess();
			Process[] processes = Process.GetProcessesByName(proc.ProcessName);

			// If there is a different instance of the system running, pass
			// the filename command to the running version of the software
			// and focus that window
			if (processes.Length > 1)
			{
				//iterate through all running target applications
				foreach (Process p in processes)
				{
					if (p.Id != proc.Id)
					{
						int result = 0;

						// Get a pointer to the main window of the already running version
						IntPtr targetWindow = p.MainWindowHandle;

						// Send the file opened to the other running instance
						if (!string.IsNullOrWhiteSpace(m_sFileToOpen))
						{
							byte[] sarr = System.Text.Encoding.Default.GetBytes(m_sFileToOpen);
							int len = sarr.Length;
							COPYDATASTRUCT cds;
							cds.dwData = (IntPtr)100;
							cds.lpData = m_sFileToOpen;
							cds.cbData = len + 1;
							result = SendMessage(targetWindow, WM_COPYDATA, IntPtr.Zero, ref cds);
						}

						// Focus the main window of the other instance
						SetForegroundWindow(p.MainWindowHandle);
					}
				}
			}
			else
			{
				Application.EnableVisualStyles();
				Application.SetCompatibleTextRenderingDefault(false);

				// This is the only running instance, create a new instance
				// of the main window and display it.
				using (Main frmMain = new Main())
				{
					if (!string.IsNullOrWhiteSpace(m_sFileToOpen))
						frmMain.OpenAtStartup.Add(m_sFileToOpen);
					Application.Run(frmMain);
				}
			}
		}

	}
}