本文以实例描述了C#实现让窗体永远在窗体最前面显示的方法，具体步骤如下：

1、新建一个窗体程序，添加一个Timer以及设置它可用并绑定事件。

2、设置窗体的TopMost属性为True

3、然后设置代码如下即可实现.

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Text;

using System.Windows.Forms;namespace jiyi

{

  public partial class Form1 : Form

  {public Form1()

    {

      InitializeComponent();

    }

    private void Form1_Load(object sender, EventArgs e)

    {

    }

    private void timer1_Tick(object sender, EventArgs e)

    {

      this.TopMost = false;

      this.BringToFront();

      this.TopMost = true;

    }

  }

}

using System.Runtime.InteropServices;

using System.Diagnostics;

using System.Reflection;

//*****************************************************

  static class Program

    {

        /// <summary>

        /// 该函数设置由不同线程产生的窗口的显示状态。

        /// </summary>

        /// <param name="hWnd">窗口句柄</param>

        /// <param name="cmdShow">指定窗口如何显示。查看允许值列表，请查阅ShowWlndow函数的说明部分。</param>

        /// <returns>如果函数原来可见，返回值为非零；如果函数原来被隐藏，返回值为零。</returns>

        [DllImport("User32.dll")]

        private static extern bool ShowWindowAsync(IntPtr hWnd, int cmdShow);

        /// <summary>

        /// 该函数将创建指定窗口的线程设置到前台，并且激活该窗口。键盘输入转向该窗口，并为用户改各种可视的记号。系统给创建前台窗口的线程分配的权限稍高于其他线程。

        /// </summary>

        /// <param name="hWnd">将被激活并被调入前台的窗口句柄。</param>

        /// <returns>如果窗口设入了前台，返回值为非零；如果窗口未被设入前台，返回值为零。</returns>

        [DllImport("User32.dll")]

        private static extern bool SetForegroundWindow(IntPtr hWnd);

        private const int WS_SHOWNORMAL = ;

        /// <summary>

        /// 应用程序的主入口点。

        /// </summary>

        [STAThread]

        static void Main()

        {

            Application.EnableVisualStyles();

            Application.SetCompatibleTextRenderingDefault(false);

            Process instance = RunningInstance();

            if (instance == null)

            {

                Form1 frm = new Form1();

                Application.Run(new Form1());

            }

            else

            {

                HandleRunningInstance(instance);

            }

        }

        /// <summary>

        /// 获取正在运行的实例，没有运行的实例返回null;

        /// </summary>

        public static Process RunningInstance()

        {

            Process current = Process.GetCurrentProcess();

            Process[] processes = Process.GetProcessesByName(current.ProcessName);

            foreach (Process process in processes)

            {

                if (process.Id != current.Id)

                {

                    if (Assembly.GetExecutingAssembly().Location.Replace("/", "\\") == current.MainModule.FileName)

                    {

                        return process;

                    }

                }

            }

            return null;

        }

        /// <summary>

        /// 显示已运行的程序。

        /// </summary>

        public static void HandleRunningInstance(Process instance)

        {

            ShowWindowAsync(instance.MainWindowHandle, WS_SHOWNORMAL); //显示，可以注释掉

            SetForegroundWindow(instance.MainWindowHandle);            //放到前端

        }

    }

//=====创建互斥体法：=====

bool blnIsRunning;

Mutex mutexApp = new Mutex(false, Assembly.GetExecutingAssembly().FullName, out   blnIsRunning);

if (!blnIsRunning)

{

    MessageBox.Show("程序已经运行！", "提示",

    MessageBoxButtons.OK, MessageBoxIcon.Exclamation);

    return;

}   

//保证同时只有一个客户端在运行

System.Threading.Mutex mutexMyapplication = new System.Threading.Mutex(false, "OnePorcess.exe");

if (!mutexMyapplication.WaitOne(, false))

{

    MessageBox.Show("程序" + Application.ProductName + "已经运行！", Application.ProductName,

    MessageBoxButtons.OK, MessageBoxIcon.Error);

    return;

}

//=====判断进程法：(修改程序名字后依然能执行)=====

Process current = Process.GetCurrentProcess();

Process[] processes = Process.GetProcessesByName(current.ProcessName);

foreach (Process process in processes)

{

    if (process.Id != current.Id)

    {

        if (process.MainModule.FileName

        == current.MainModule.FileName)

        {

            MessageBox.Show("程序已经运行！", Application.ProductName,

            MessageBoxButtons.OK, MessageBoxIcon.Exclamation);

            return;

        }

    }

}