c# 应用程序只运行一个实例

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;
using System.Diagnostics;
using System.Reflection;

namespace OneInstance
{
    /// <summary>
    /// Class with program entry point.
    /// </summary>
    internal sealed class Program
    {
        
        //Api声明，并声明一

        [DllImport("User32.dll")]  private static extern bool ShowWindowAsync(    IntPtr hWnd, int cmdShow);
        [DllImport("User32.dll")]  private static extern bool    SetForegroundWindow(IntPtr hWnd);
        private const int WS_SHOWNORMAL = 1;

        [STAThread]  public static void Main()
        {
            //得到正在运行的例程
            Process instance = RunningInstance();
            if (instance == null)
            {
                //如果没有其它例程，就新建一个窗体
                Application.Run (new MainForm());
            }
            else
            {
                //处理发现的例程
                HandleRunningInstance(instance);
            }
        }
        public static Process RunningInstance()
        {
            Process current = Process.GetCurrentProcess();
            Process[] processes = Process.GetProcessesByName (current.ProcessName);
            //遍历正在有相同名字运行的例程
            foreach (Process process in processes)
            {
                //忽略现有的例程
                if (process.Id != current.Id)
                {
                    //确保例程从EXE文件运行
                    if (Assembly.GetExecutingAssembly().Location.Replace("/", "\\") ==current.MainModule.FileName)
                    {
                        //返回另一个例程实例
                        return process;
                    }
                }
            }
            //没有其它的例程，返回Null
            return null;
        }
        public static void HandleRunningInstance(Process instance)
        {
            //确保窗口没有被最小化或最大化
            ShowWindowAsync (instance.MainWindowHandle , WS_SHOWNORMAL);
            //设置真实例程为foreground window
            SetForegroundWindow (instance.MainWindowHandle);
        }
        
    }
}