QQ基本代码

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;
using MyQQ;
namespace qq
{
    public partial class LoginFrm : Form
    {
        public LoginFrm()
        {
            InitializeComponent();
        }
        //窗体加载时
        private void LoginFrm_Load(object sender, EventArgs e)
        {
            this.picFace.Image = this.imageFace.Images[0];
        }
        //文本框改变时发生的窗体
        private void txtNum_TextChanged(object sender, EventArgs e)
        {
            if (this.txtNum.Text.Trim().Length == 5)
            {
                this.txtPwd.Focus();
                string sql = string.Format("select FaceId from Users where Id = {0}", this.txtNum.Text);
                SqlCommand cmd = new SqlCommand(sql, DbHelper.conn);
                try
                {
                    DbHelper.opendb();
                    this.picFace.Image = this.imageFace.Images[Convert.ToInt32(cmd.ExecuteScalar())];
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.ToString());
                }
                finally
                {