public MainForm()
        {
            InitializeComponent();
            button1.Click += new EventHandler(btn_Click);
            button2.Click += new EventHandler(btn_Click);
            button3.Click += new EventHandler(btn_Click);
            button4.Click += new EventHandler(btn_Click);
            button5.Click += new EventHandler(btn_Click);
            leftMenu();

        }
        private void leftMenu()
        {
            button5.Tag = button4.Tag = button3.Tag = button1.Tag = button2.Tag = 1;
            panel5.Visible = panel4.Visible = panel3.Visible = panel1.Visible = panel2.Visible = false;
        }
        //折疊按鈕
        private void btn_Click(object sender, EventArgs e)
        {
            Button btn = sender as Button;
            foreach (Control x in splitContainer1.Panel1.Controls)
            {
                if (x.Name == "panel" + btn.Name[btn.Name.Length - 1])
                {
                    if ((int)btn.Tag == 2)
                    {
                        btn.Tag = 1;
                        x.Visible = false;
                        return;
                    }
                    else
                    {
                        btn.Tag = 2;
                        x.Visible = true;
                    }
                    break;
                }
            }
            int tmpUp = Convert.ToInt32(btn.Name[btn.Name.Length - 1].ToString()) - 1;
            int tmpDown = Convert.ToInt32(btn.Name[btn.Name.Length - 1].ToString()) + 1;

            foreach (Control x in splitContainer1.Panel1.Controls)
            {
                if (tmpUp != 1)
                {
                    if (x.Name == "panel" + tmpUp) x.Visible = false;
                    if (x.Name == "button" + tmpUp) x.Tag = 1;
                }
                if (x.Name == "panel" + tmpDown) x.Visible = false;
                if (x.Name == "button" + tmpDown) x.Tag = 1;
            }

        }

左側菜單，2個控件一個按妞和一個面板，通過Name屬性，使按鈕和面板聯系在一起，

winfrom 左側菜單