winform实现只能打开一次

//在程序的main函数中加入以下代码 
bool createdNew; 
System.Threading.Mutex instance = new System.Threading.Mutex(true, "MutexName", out createdNew); 
if (createdNew) 
{ 
　　Application.Run(new LoginForm()); 
　　instance.ReleaseMutex(); 
} 
else 
{ 
　　Application.Exit(); 
} 
//还可以写成以下形式，一个窗体只能启动一次 
Form1 a = new Form1(); 
bool createdNew; 
System.Threading.Mutex instance = new System.Threading.Mutex(true, "MutexName", out createdNew); 
if (createdNew) 
{ 
　　a.ShowDialog(); 
　　instance.ReleaseMutex(); 
} 
else 
{ 
　　a.Close(); 
}

private static bool HasRunning()
{
    Process currentProcess = Process.GetCurrentProcess();
    Process[] processCollection = Process.GetProcessesByName(currentProcess.ProcessName);
    foreach (Process p in processCollection)
    {
        if (p.Id == currentProcess.Id)  //检查ID是否相同
        {
            return true;
        }
    }
    return false;
}

//预防程序启动多个
bool newMutexCreated = true;
using (new Mutex(true, Assembly.GetExecutingAssembly().FullName, out newMutexCreated))
{
if (!newMutexCreated)
{
MessageBox.Show("程序已启动！请不要启动多个程序");
System.Environment.Exit(0);
}
else
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new frmMain());
}
}