ListBox重复项检测

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;

namespace Ex067

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        private void btn_add_Click(object sender, EventArgs e)

        {

            if (txt_add.Text == "")        //文本框为空

            {

                MessageBox.Show("添加的内容不能为空！");

                txt_add.Focus();              //获取焦点

            }

            else

            {

                if (listBox1.Items.Count > 0) //判断列表框中是否有项

                {

                    //循环比较是否有重复项，有则放弃添加

                    for (int i = 0; i < listBox1.Items.Count; i++)

                    {

                        if (string.Compare(listBox1.Items[i].ToString(), txt_add.Text) == 0)

                        {

                            MessageBox.Show("列表框中已有相同项，不能添加！");       //提示信息

                            txt_add.Text = "";    //清空文本框

                            txt_add.Focus();

                            return;

                        }

                    }

                    listBox1.Items.Add(txt_add.Text.ToString());      //添加项

                    txt_add.Text = "";

                }

                else

                {

                    listBox1.Items.Add(txt_add.Text.ToString());    //将文本框中的数据添加到列表框

                    txt_add.Text = "";

                }

            }

        }

    }

}