public partial class Frm1

{

[DllImport("user32.dll")]

private static extern bool

SetForegroundWindow(IntPtr hWnd);

[DllImport("user32.dll")]

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

[DllImport("user32.dll")]

private static extern bool IsIconic(IntPtr hWnd);

// 消息函数

[DllImport("user32.dll", EntryPoint = "PostMessageA")]

public static extern bool PostMessage(IntPtr hWnd, int Msg, int wParam, int lParam);

[DllImport("user32.dll")]

public static extern IntPtr FindWindow(string strclassName, string strWindowName);

[DllImportAttribute("user32.dll")]

public static extern int SendMessage(IntPtr hWnd, int Msg, int wParam, int lParam);

public const int WM_SYSCOMMAND = 0x0112;

public const int SC_MAXIMIZE = 0xF030;//窗体最大化消息

public const int SC_NOMAL = 0xF120;//窗体还原消息

private void Frm1_Load(object sender, EventArgs e)

{

CheckAppExists();

}

//判断是否重复打开

public void CheckAppExists()

{

string name = System.Diagnostics.Process.GetCurrentProcess().ProcessName;

System.Diagnostics.Process[] myProcesses = System.Diagnostics.Process.GetProcessesByName(name);//获取指定的进程名

if (myProcesses.Length > 1) //如果可以获取到知道的进程名则说明已经启动

{

MessageBox.Show("程序已启动！");

Process[] process = Process.GetProcessesByName(name);//在所有已启动的进程中查找需要的进程；

if (process.Length > 0)//如果查找到

{

IntPtr handle = process[0].MainWindowHandle;

IntPtr hWnd = process[0].MainWindowHandle;

SendMessage(hWnd, WM_SYSCOMMAND, SC_NOMAL, 0);

SetForegroundWindow(hWnd);

}

Application.Exit();//关闭系统

}

}

}

参考网站：(16条消息) C# 如何判断并且激活,最大化已有的外部应用程序的窗口？ (源码例程)_jamex的博客-CSDN博客_c# 激活已经运行的程序