c# - 添加新的 TabPage 问题

Question

这个想法是在双击时为包含主题、发件人和内容的电子邮件打开一个新的标签页MailList。但它可以在第一次双击打开。:(

private void MailList_DoubleClick(object sender, EventArgs e)
{
    TabPage newtab = new TabPage();
    Mime m=EncodingMail(MailTree.SelectedNode.Text, MailList.FocusedItem.Text);

    newtab.Text = m.MainEntity.Subject;
    if (m.Attachments.Length == 0)   attachmentTabPages2.Visible=false;
    else
    {
        attachmentTabPages2.Visible = true;
        for (int j = 0; j < m.Attachments.Count(); j++)
        {
            ListViewItem item1 = new ListViewItem();
            item1.Text = m.Attachments[j].ContentDisposition_FileName;
            attachmentTabPages2.Items.Add(item1);
        }
    }
    //ListViewItem item = sender as ListViewItem;   
    webBrowser2.DocumentText = m.BodyHtml;
    FromTabPage2.Text="From: " + m.MainEntity.From.ToAddressListString();
    ToTabPages2.Text = "To: " + m.MainEntity.To.ToAddressListString();
    SubjectTabPage2.Text = "Subject: " + m.MainEntity.Subject;
    DateTimeTabPages2.Text = "Date: " + m.MainEntity.Date.ToShortDateString();
    foreach (Control control in tabPage2.Controls)
    {
        newtab.Controls.Add(control);
    }
    Acc1Tab.TabPages.Add(newtab);
    Acc1Tab.SelectedTab = newtab;
}