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本文介绍了一个简单的国家查询功能实现方式，通过输入国家名称，系统能够返回对应的国家ID及名称列表。利用C#语言实现了数据库查询操作，并展示了如何响应用户输入进行实时反馈。

CountClass countClass=new CountClass ();

//类

{

/// <returns>返回国籍名与ＩＤ</returns>
public static ArrayList getCountryArrayList(string cname)
{

            ArrayList arraylist = new ArrayList();
            string sql = "select C_ID ,c_namee from country where c_namee like '%" + cname + "%'";
            SqlConnection con = new SqlConnection(SqlHelper.SQLConnectionString);
            SqlDataReader dr = SqlHelper.ExecuteReader(con, CommandType.Text, sql, null);
            while (dr.Read())
            {
                arraylist.Add(dr["C_ID"].ToString() + "," + dr["c_namee"].ToString());

}
return arraylist;

}

/// <returns>返回国籍名与ＩＤ</returns>
public static string getCountryID(string cname)
{

            string countryid = string.Empty;
            string sql = "select C_ID from country where c_namee ='" + cname + "'";
            SqlConnection con = new SqlConnection(SqlHelper.SQLConnectionString);
            SqlDataReader dr = SqlHelper.ExecuteReader(con, CommandType.Text, sql);
            while (dr.Read())
            {
                countryid = dr[0].ToString();

            }
            dr.Close();
            return countryid;

}

///页面事件

private void txtCountry_KeyPress(object sender, KeyPressEventArgs e)
            {
                try
                {
                    if (e.KeyChar == (char)Keys.Enter)
                    {

                        if (lstCountry != null)
                        {
                            if (lstCountry.Items.Count != 0)
                            {
                                lstCountry.Items.Clear();
                            }

                        }
                        ArrayList arraylist = countClass.getCountryArrayList(this.txtCountry.Text);
                        if (arraylist != null)
                        {
                            if (arraylist.Count != 0)
                            {

                                for (int i = 0; i < arraylist.Count; i++)
                                {
                                    lstCountry.Items.Add((arraylist[i].ToString().Split(','))[1].ToString());

                                }
                                this.lstCountry.Visible = true;
                            }
                            else
                            {
                                MessageBox.Show("没有这个国家名称，请重新录入", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
                                this.txtCountry.Focus();
                                this.txtCountry.Text = "";
                                this.lstCountry.Visible = false;
                            }

}
}

                }
                catch (Exception ex)
                {
                    ex.GetBaseException();
                }
            }

private void lstCountry_DoubleClick(object sender, EventArgs e)
            {
                if (lstCountry.Items.Count != 0)
                {
                    this.txtCountry.Text = this.lstCountry.Text;
                    countryidlist = countClass.getCountryID(this.txtCountry.Text);
                    this.lstCountry.Visible = false;
                }
            }