// 
            // toolBarButton1
            // 
            this.toolBarButton1.Style = System.Windows.Forms.ToolBarButtonStyle.ToggleButton;
            this.toolBarButton1.Text = "显示子窗体";
private void toolBar1_ButtonClick(object sender, System.Windows.Forms.ToolBarButtonClickEventArgs e)
        {
            if(e.Button == toolBarButton1)//显示子窗口按钮被按下
            {
                ChildForm form = new ChildForm();
                form.MdiParent = this;
                form.Disposed+=new EventHandler(form_Disposed);//捕获子窗口的销毁事件
                form.Show();
            }
        }

        /// <summary>
        /// 子窗口销毁事件
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void form_Disposed(object sender, EventArgs e)
        {
            ///弹起工具栏的按钮
            toolBarButton1.Pushed = false;
        }