C# WinForm只允许运行一个窗体实例

using System;
using System.Collections.Generic;
using System.Windows.Forms;
using XLuSharpLibrary.DbAccess;
using System.Runtime.InteropServices;//使用DllImport的必须。
using System.Diagnostics;//引入Process 类
namespace BHair
{
    static class Program
    {
        private const int WS_SHOWNORMAL = 1;
        [DllImport("User32.dll")]
        private static extern bool ShowWindowAsync(IntPtr hWnd, int cmdShow);
        [DllImport("User32.dll")]
        private static extern bool SetForegroundWindow(IntPtr hWnd);
        /// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [STAThread]
        static void Main()
        {
            Process instance = GetRunningInstance();
            if (instance == null)
            {
                Application.EnableVisualStyles();
                Application.SetCompatibleTextRenderingDefault(false);
                String ConString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + Application.StartupPath.ToString() + "\\db\\FFHair.mdb";

                DbConfig.DbConnection = ConString;
                DbConfig.DbType = DBType.Access;
                Application.Run(new LoginForm());
            }
            else
            {
                HandleRunningInstance(instance);
            }
        }
        /// <summary>
        /// 获取当前是否具有相同进程。
        /// </summary>
        /// <returns></returns>
        public static Process GetRunningInstance()
        {
            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 (System.Reflection.Assembly.GetExecutingAssembly().Location.Replace("/", "\\") == current.MainModule.FileName)
                        return process;
            }
            return null;
        }
        /// <summary>
        /// 激活原有的进程。
        /// </summary>
        /// <param name="instance"></param>
        public static void HandleRunningInstance(Process instance)
        {
            ShowWindowAsync(instance.MainWindowHandle, WS_SHOWNORMAL);
            SetForegroundWindow(instance.MainWindowHandle);
        }
    }
}