MDI窗体容器中,相同窗体只显示一个

private frmChannelInfo myChannelInfo = null;

        private void tsbChannelInfo_Click(object sender, EventArgs e)
        {
            if (myChannelInfo != null && myChannelInfo.Created)
            {
                myChannelInfo.Focus();
                return;
            }
            myChannelInfo = new frmChannelInfo();
            myChannelInfo.MdiParent = this;
            myChannelInfo.Show();
        }