private void ShowNewForm(object sender, EventArgs e)
        {
            frm_Networking_Maintenance childForm = new frm_Networking_Maintenance();
            childForm.MdiParent = this;            
            childForm.Show();
            this.notifyIcon1.Visible = false; [font color=#FF0000]//加了这句都没有用，每次点父窗口菜单，打开一个子窗口，可下方的notifyIcon1图标就会多出一个，要关了再点，又会再多出一个图标，要怎样作才可以让程序只显示一个图标呀？请老师指点一下，谢谢。[/font]
        }






[font color=#FF0000]//以下是完整的代码[/font]

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;

using System.Data.SqlClient; 



namespace IT部门管理系统
{
    public partial class frm_main : Form
    {
        

        public frm_main()
        {
            InitializeComponent();
        }

        private void ShowNewForm(object sender, EventArgs e)
        {
            frm_Networking_Maintenance childForm = new frm_Networking_Maintenance();
            childForm.MdiParent = this;            
            childForm.Show();
            this.notifyIcon1.Visible = false;
        }

        private void OpenFile(object sender, EventArgs e)
        {
            OpenFileDialog openFileDialog = new OpenFileDialog();
            openFileDialog.InitialDirectory = Environment.GetFolderPath(Environment.SpecialFolder.Personal);
            openFileDialog.Filter = "文本文件(*.txt)|*.txt|所有文件(*.*)|*.*";
            if (openFileDialog.ShowDialog(this) == DialogResult.OK)
            {
                string FileName = openFileDialog.FileName;
            }
        }

        private void SaveAsToolStripMenuItem_Click(object sender, EventArgs e)
        {
            SaveFileDialog saveFileDialog = new SaveFileDialog();
            saveFileDialog.InitialDirectory = Environment.GetFolderPath(Environment.SpecialFolder.Personal);
            saveFileDialog.Filter = "文本文件(*.txt)|*.txt|所有文件(*.*)|*.*";
            if (saveFileDialog.ShowDialog(this) == DialogResult.OK)
            {
                string FileName = saveFileDialog.FileName;
            }
        }

        private void ExitToolsStripMenuItem_Click(object sender, EventArgs e)
        {
            this.Close();
        }

        private void CutToolStripMenuItem_Click(object sender, EventArgs e)
        {
        }

        private void CopyToolStripMenuItem_Click(object sender, EventArgs e)
        {
        }

        private void PasteToolStripMenuItem_Click(object sender, EventArgs e)
        {
        }               

        private void CascadeToolStripMenuItem_Click(object sender, EventArgs e)
        {
            LayoutMdi(MdiLayout.Cascade);
        }

        private void TileVerticalToolStripMenuItem_Click(object sender, EventArgs e)
        {
            LayoutMdi(MdiLayout.TileVertical);
        }

        private void TileHorizontalToolStripMenuItem_Click(object sender, EventArgs e)
        {
            LayoutMdi(MdiLayout.TileHorizontal);
        }

        private void ArrangeIconsToolStripMenuItem_Click(object sender, EventArgs e)
        {
            LayoutMdi(MdiLayout.ArrangeIcons);
        }

        private void CloseAllToolStripMenuItem_Click(object sender, EventArgs e)
        {
            foreach (Form childForm in MdiChildren)
            {
                childForm.Close();
            }
        }

        private void optionsToolStripMenuItem_Click(object sender, EventArgs e)
        {
            frm_dbConf frmdb = new frm_dbConf();    //显示主窗体
            frmdb.Show(); 
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            tsslSTime.Text = "系统时间：" + DateTime.Now.ToString();
        }

        private void frm_main_Load(object sender, EventArgs e)
        {

            frm_note childForm = new frm_note();
            childForm.MdiParent = this;
            childForm.Show();

            timer1.Start();
            tsslLTime.Text = "|登录时间：" + DateTime.Now.ToShortTimeString();
            tsslSTime.Text = "|系统时间：" + DateTime.Now.ToString();

            this.notifyIcon1.Visible = false;
            
        }

        private void saveToolStripMenuItem_Click(object sender, EventArgs e)
        {

        }

        private void 管理ToolStripMenuItem_Click(object sender, EventArgs e)
        {

        }

        private void FrmMain_FormClosing(object sender, FormClosingEventArgs e)
        {
            //if (MessageBox.Show("将要要关闭窗体，是否继续？", "询问", MessageBoxButtons.YesNo) == DialogResult.Yes)
            //{
            //    e.Cancel = false;
            //}
            //else
            //{
            //    e.Cancel = true;
            //}

            e.Cancel = true;
            this.Hide();
            this.notifyIcon1.Visible = true;  
        }

        private void notifyIcon1_MouseDoubleClick(object sender, MouseEventArgs e)
        {
            if (this.Visible == true)   //根据窗口的显示和隐藏设置Trayico对象的显示   
            {
                this.Hide();
                this.notifyIcon1.Visible = true;
            }
            else
            {
                this.Show();
                this.notifyIcon1.Visible = false;
            }   

        }

        private void 退出系统ToolStripMenuItem_Click(object sender, EventArgs e)
        {

            Application.ExitThread(); 
            this.notifyIcon1.Visible = false;
        }

        private void 打开主界面ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            this.Show();
            this.notifyIcon1.Visible = false;
        }


    }
}