简单版用户登录

简单实现：

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;
using System.Text.RegularExpressions;

namespace 用户登录
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void but1_Click(object sender, EventArgs e)
        {
            if (string.IsNullOrWhiteSpace(textb1.Text) ||
                textb2.Text == "" ||
                textb3.Text == "")
            {
                MessageBox.Show("请输入正确的信息");
                return;
            }
            if (textb2.Text.Trim() != textb3.Text.Trim())
            {
                MessageBox.Show("两次密码输入不正确");
                return;
            }
            string uid = textb1.Text.Trim();
            string pwd = textb2.Text.Trim();
            string sqlconn = @"server=.;database=MyDataBase;Integrated security=true";
            string sql = string.Format("insert into UseLogin(name,pwd) values('{0}','{1}');", uid, pwd);
            using (SqlConnection conn = new SqlConnection(sqlconn))
            {
                using (SqlCommand cmd = new SqlCommand(sql, conn))
                {
                    if (conn.State == ConnectionState.Closed)
                    {
                        conn.Open();
                    }
                    try
                    {
                        int res = cmd.ExecuteNonQuery();
                        textb1.Clear();
                        textb2.Text = string.Empty;
                        textb3.Text = "";
                        MessageBox.Show(string.Format("{0}行受影响", res));
                    }
                    catch (Exception ex)
                    {
                        MessageBox.Show(ex.Message);
                    }
                }
            }
        }
        private void textb1_Leave(object sender, EventArgs e)
        {
            string sqlconn = @"server=.;database=MyDataBase;Integrated security=true";
            string sql = string.Format(@"select count(*) from uselogin where name='{0}'", textb1.Text.Trim());
            using (SqlConnection conn = new SqlConnection(sqlconn))
            {
                using (SqlCommand cmd = new SqlCommand(sql, conn))
                {
                    if (conn.State == ConnectionState.Closed)
                    {
                        conn.Open();
                    }
                    int set = Convert.ToInt32(cmd.ExecuteScalar());
                    if (Regex.IsMatch(textb1.Text.Trim(), @"^\w{0,10}$"))
                    {
                        if (set != 0)
                        {
                            label4.ForeColor = Color.Red;
                            label4.Text = "该用户名存在，请重新输入";
                        }
                        else
                        {
                            label4.ForeColor = Color.Blue;
                            label4.Text = "√";
                        }
                    }
                    else
                    {
                        label4.ForeColor = Color.Red;
                        label4.Text = "该用户长度，请重新输入";
                    }
                }
            }
        }
    }
}