WPF 只允许打开一个实例

                    // 确保不存在程序的其他实例
                    singleInstanceWatcher = new Semaphore(
                        0, // Initial count.
                        1, // Maximum count.
                        Assembly.GetExecutingAssembly().GetName().Name, out createdNew);
                    if (createdNew)
                    {
                        //之前没有运行过
                    }
                    else
                    {
                      //重复运行
                        MessageBox.Show("请不要重复运行(ノ｀Д)ノ");
                        Environment.Exit(-2);
                    }

            string mutexName = Properties.Resources.ProgramTitle + "Mutex";
            singleInstanceWatcher = new Mutex(false, mutexName, out createdNew);
            if (!createdNew)
            {
                MessageBox.Show("程序已经运行!", "错误", MessageBoxButton.OK, MessageBoxImage.Error);
                Environment.Exit(-1);
            }

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();
}