C#嵌入子窗体，判断子窗体是否打开了

/// <summary>
        /// 嵌入子窗体，判断子窗体是否打开了
        /// </summary>
        public static Form1 f;
        public void Form1Show()
        {

            if (f == null || f.IsDisposed)
            {
                f = new Form1
                {
                    WindowState = FormWindowState.Maximized,
                    FormBorderStyle = FormBorderStyle.None,
                    TopLevel = false,
                    Parent = this.tabPage1
                };

                f.Show();
            }
        }