给MDI程序加上标签栏之新解－感谢沐枫！

去掉了原有基类，所有功能都在主窗体中完成，拖入一个TabControl，加入以下代码：

MainFormMDI_MdiChildActivate#region MainFormMDI_MdiChildActivate
private void MainFormMDI_MdiChildActivate(object sender, System.EventArgs e)
        {
            if (this.ActiveMdiChild != null)
            {
this.tabControl1.Visible = true;
                for (int i = 0; i < this.tabControl1.TabCount; i++)
                { 
                    if(this.ActiveMdiChild.Equals(tabControl1.TabPages[i].Tag))
                    {
                        this.tabControl1.SelectedTab = this.tabControl1.TabPages[i];
                        break;
                    }
                }
            }
            else
            {
      this.tabControl1.Visible = false;
            }        
        }

        #endregion

把MDI窗口与TabControl关联并加入快捷菜单#region 把MDI窗口与TabControl关联并加入快捷菜单

        private void tabControl1_SelectedIndexChanged(object sender, System.EventArgs e)
        {
            foreach (Form childForm in this.MdiChildren) 
            {
                //Check for its corresponding MDI child form
                if (this.tabControl1.SelectedTab != null && childForm.Equals(tabControl1.SelectedTab.Tag)) 
                {
                    //Activate the MDI child form
                    childForm.Select();
                }
            }
        }
        private void AddMDIChildToTabCtrl(Form frmChild)
        {
            frmChild.MdiParent = this;
            frmChild.Closed += new EventHandler(frmChild_Closed);

            //child Form will now hold a reference value to the tab control
            //frmChild.TabCtrl = tabControl1;

            //Add a Tabpage and enables it
            TabPage tp = new TabPage();
            tp.Parent = tabControl1;
            tp.Text = frmChild.Text;
            tp.Tag = frmChild;
            tp.Show();

            //child Form will now hold a reference value to a tabpage
            frmChild.Show();
            this.tabControl1.SelectedTab = tp;
        }

        void frmChild_Closed(object sender, EventArgs e)
        {
            this.RemoveTabPageFromTabCtrl();
        }

        private void ctxmnuClose_Click(object sender, System.EventArgs e)
        {
            if(this.tabControl1.Visible && tabControl1.TabCount > 0)
            {
                Form childForm = this.ActiveMdiChild;
                childForm.Close();
                this.RemoveTabPageFromTabCtrl();  
            }
        }
        /**//// <summary>
        /// 在子窗体关闭时移除对应的TabPage
        /// </summary>
        private void RemoveTabPageFromTabCtrl()
        {
            for (int i = 0; i < this.tabControl1.TabCount; i++)
            {
                if (this.ActiveMdiChild.Equals(tabControl1.TabPages[i].Tag))
                {
                    this.tabControl1.TabPages.Remove(this.tabControl1.TabPages[i]);
                    break;
                }
            }
        }
        private void tabControl1_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
        {
            if(e.Button == MouseButtons.Right)
            {
                Rectangle rct;
                for(int i=0; i< tabControl1.TabPages.Count; i++)
                {
                    rct = tabControl1.GetTabRect(i);

                    if(rct.Contains(e.X, e.Y))
                    {
                        //tabControl1.SelectedIndex = i;
                        tabControl1.SelectedTab = tabControl1.TabPages[i];
                        break;
                    }
                }
            }
        }

        #endregion

创建MDI子窗口时，调用AddMDIChildToTabControl即可。