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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;namespace LJL{       public partial class Form1 : Form    {         public Form1()        {            InitializeComponent();        }            private void button2_Click(object sender, EventArgs e)        {          DialogResult result=MessageBox.Show("确定退出吗?", "提示", MessageBoxButtons.YesNo, MessageBoxIcon.Question);          if (result == DialogResult.Yes)          {              this.Close();          }        }        private void Form1_Click(object sender, EventArgs e)        {            if (this.BackColor == Color.Red)            {                this.BackColor = Color.Yellow;            }            else if (this.BackColor == Color.Yellow)            {                this.BackColor = Color.Green;            }            else            {                this.BackColor = Color.Red;            }        }            public const string CAPTION = "输入提示";        public const string ADMIN = "教员";        private void button1_Click_1(object sender, EventArgs e)        {            string mingzi = textBox1.Text.Trim();                if (CheckInput())                {                    if (this.comboBox1.Text.Equals(ADMIN))                    {                        guanliyuan guanli = new guanliyuan();                        guanli.name = mingzi;                        guanli.Show();                    }                    this.Hide();                }            }                public bool CheckInput()        {            if (this.label1.Text.Trim().Equals(string.Empty))            {                MessageBox.Show("请输入用户名", CAPTION, MessageBoxButtons.OK, MessageBoxIcon.Information);                this.label1.Focus();                return false;            }            else if (this.label2.Text.Trim().Equals(string.Empty))            {                MessageBox.Show("请输入密码", CAPTION, MessageBoxButtons.OK, MessageBoxIcon.Information);                this.label2.Focus();                return false;            }            else if (this.label3.Text.Trim().Equals(string.Empty))            {                MessageBox.Show("请选择登录类型", CAPTION, MessageBoxButtons.OK, MessageBoxIcon.Information);                this.label3.Focus();                return false;            }            else            {                return true;            }        }        public bool CheckUser(ref string message)        {            bool i = false;            string mingzi =textBox1.Text.Trim();            string mima = textBox2.Text.Trim();            StringBuilder sb = new StringBuilder();            if (label3.Equals(ADMIN))            {                sb.AppendFormat("SELECT COUNT(*) FROM [Table_1]" + " WHERE [mingzi]='{0}' AND [mima]='{1}'", mingzi, mima);            }             int count = 0;            DEHelper dbhelper = new DEHelper();            try            {                SqlCommand comm = new SqlCommand(sb.ToString(), dbhelper.Connection);                dbhelper.OpenConnection();                count = (int)comm.ExecuteScalar();                if (count > 0)                {                    i = true;                }                else                {                    message = "用户名或密码不存在";                    i = false;                }            }            catch (Exception)            {                message = "系统发生错误,请稍后再试";                i = false;            }            finally            {                dbhelper.CloseConnection();            }            return i;        }        }           }

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;namespace LJL{    public partial class guanliyuan : Form    {        public string name = "";        public guanliyuan()        {            InitializeComponent();        }        private void guanliyuan_Load(object sender, EventArgs e)        {            this.label1.Text = name;        }    }}