winform单例窗体打开、关闭、隐藏

         private void OpenForm(Type type)
        {
            if (Application.OpenForms[type.Name] != null)
            {
                Application.OpenForms[type.Name].Show();
            }
            else
            {
                //Assembly asm = Assembly.Load(type.Assembly.FullName);
                Form NewForm = (Form)Activator.CreateInstance(type);
                NewForm.Show();
            }
        }

       OpenForm(typeof(Form1));