先添加notifyicon控件notifyIcon1 

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;namespace notifyIconShow{    public partial class ColdJoke : Form    {        #region        //创建NotifyIcon对象         NotifyIcon notifyicon = new NotifyIcon();        //创建托盘图标对象         Icon ico = new Icon("snow.ico");        //创建托盘菜单对象         ContextMenu notifyContextMenu = new ContextMenu();        #endregion        public ColdJoke()        {            InitializeComponent();        }        #region 托盘提示        private void Form1_Load(object sender, EventArgs e)        {            //设置鼠标放在托盘图标上面的文字             this.notifyIcon1.Text = "笑话";        }        #endregion        #region 隐藏任务栏图标、显示托盘图标        private void Form1_SizeChanged(object sender, EventArgs e)        {            //判断是否选择的是最小化按钮             if (WindowState == FormWindowState.Minimized)            {                //托盘显示图标等于托盘图标对象                 //注意notifyIcon1是控件的名字而不是对象的名字                 notifyIcon1.Icon = ico;                //隐藏任务栏区图标                 this.ShowInTaskbar = false;                //图标显示在托盘区                 notifyicon.Visible = true;            }        }        #endregion        #region 还原窗体        private void notifyIcon1_DoubleClick(object sender, EventArgs e)        {            //判断是否已经最小化于托盘             if (WindowState == FormWindowState.Minimized)            {                //还原窗体显示                 WindowState = FormWindowState.Normal;                //激活窗体并给予它焦点                 this.Activate();                //任务栏区显示图标                 this.ShowInTaskbar = true;                //托盘区图标隐藏                 notifyicon.Visible = false;            }        }        #endregion    }}