MDI 父子窗体

        public bool checkChildFrmExist(string childFrmName)
        {
            foreach (Form childFrm in this.ParentForm.MdiChildren)
            {
                if (childFrm.Text == childFrmName)
                {
                    childFrm.Activate();
                    return true;
                }
            }
            return false;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (this.checkChildFrmExist("Form2") == true)
            {
                return;
            }
            Form2 f2 = new Form2();
            f2.MdiParent = this.MdiParent;
            f2.Show();
        }