单例模式的创建：

public class Myclass

{

　　private Myclass()

{

}

public static Myclass Instance

{

get
            {
                if (_instance==null||_instance.IsDisposed)//窗体应用程序才有IsDisposed
                {
                    _instance=  new MemberForm();
                }
                return _instance;
            }

}

}