public static Process GetExistProcess()  
{  
    Process currentProcess = Process.GetCurrentProcess(); // 當(dāng)前程序  
    foreach (Process process in Process.GetProcessesByName(currentProcess.ProcessName))  
    {  
        if (process.Id != currentProcess.Id) // 找到其他同名進(jìn)程  
        {  
            return process; // 返回已運(yùn)行的進(jìn)程  
        }  
    }  
    return null; // 沒有其他實(shí)例  
}  

static class Program  
{  
    [STAThread]  
    static void Main()  
    {  
        Application.EnableVisualStyles();  
        Application.SetCompatibleTextRenderingDefault(false);  

        var runningProcess = GetExistProcess();  
        if (runningProcess != null) // 如果有實(shí)例運(yùn)行  
        {  
            IntPtr mainWindowHandle = runningProcess.MainWindowHandle;  
            if (mainWindowHandle == IntPtr.Zero) // 窗口被隱藏  
            {  
                mainWindowHandle = FindWindow(null, "唯一程序");  
            }  
            ShowWindowAsync(mainWindowHandle, 1); // 顯示窗口  
            SetForegroundWindow(mainWindowHandle); // 置于前臺  
        }  
        else  
        {  
            Application.Run(new MainForm()); // 啟動新實(shí)例  
        }  
    }  
}  

[DllImport("User32.dll", EntryPoint = "FindWindow")]  
public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);  

[DllImport("user32.dll")]  
public static extern bool ShowWindowAsync(IntPtr hWnd, int nCmdShow);  

[DllImport("user32.dll ")]  
public static extern bool SetForegroundWindow(IntPtr hWnd);  

static Mutex mutex = new Mutex(true, "UniqueAppName", out bool createdNew);  
    if (!createdNew)  
    {  
    // 已經(jīng)有實(shí)例運(yùn)行  
    return;  
    }