第一章 所有上机练习

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Data;using System.Data.SqlClient;namespace MySchool{    public class DBHelper    {        private string connString = @"Data Source=.;Initital Catalog = MySchool; User ID=sa;Pwd=bdqn";        private SqlConnection connection;        public SqlConnection Connection        {            get            {                if (connection == null)                {                    connection = new SqlConnection(connString);                }                return connection;            }        }        public void OpenConnection()        {            if (connection.State == ConnectionState.Closed)            {                connection.Open();            }            else if(connection.State == ConnectionState.Broken)            {                connection.Close();                connection.Open();            }        }        public void CloseConnection()        {            if (connection.State == ConnectionState.Open || connection.State == ConnectionState.Broken)            {                connection.Close();            }        }    }}

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 MySchool{    public partial class FrmAdminMainin : Form    {        public string userId = string.Empty;        public FrmAdminMainin()        {            InitializeComponent();        }        private void FrmAdminMainin_Load(object sender, EventArgs e)        {            textBox1.Text = userId;                   }        public const string ADMIN = "系统管理员";        private void textBox1_TextChanged(object sender, EventArgs e)        {            if (CheckInput())            {                string message = string.Empty;                if (CheckUser(ref message))                {                    if (this.cboLoginType.Text.Equals(ADMIN))                    {                        FrmAdminMainin frmAdmin = new FrmAdminMainin();                        frmAdmin.Show();                    }                    this.Hide();                }            }        }        public bool CheckUser(ref string message)        {            bool isValidUser = false;            string userName = textBox1.Text.Trim();            string userPwd = textBox2.Text.Trim();            StringBuilder sb = new StringBuilder();            if (cboLoginType.Equals(ADMIN))            {                sb.AppendFormat("SELECT COUNT(*) FROM [Admin]" + " WHERE [LoginId] = '{0}' AND [LoginPwd]='{1}'", userName, userPwd);            }            int count = 0;            DBHelper dbhelper = new DBHelper();            try            {                SqlCommand command = new SqlCommand(sb.ToString(), dbhelper.Connection);                dbhelper.OpenConnection();                count = (int)command.ExecuteScalar();                if (count > 0)                {                    isValidUser = true;                }                else                {                    message = "用户名或密码不存在!";                    isValidUser = false;                }            }            catch (Exeception ex)            {                message = "系统发生错误,请稍后再试!";                isValidUser = false;            }            finally            {                dbhelper.CloseConnection();            }            return isValidUser;        }    }}

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 MySchool{    public partial class Form1 : Form    {        public Form1()        {            InitializeComponent();        }        private void checkBox2_CheckedChanged(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;            }        }        private void checkBox4_CheckedChanged(object sender, EventArgs e)        {        }        public const string CAPTION = "输入提示";        private void denglu_Click(object sender, EventArgs e)        {            if (CheckInput())            {                            }        }        public bool CheckInput()        {            if (this.textBox1.Text.Trim().Equals(string.Empty))            {                MessageBox.Show("请输入用户名", CAPTION, MessageBoxButtons.OK, MessageBoxIcon.Information);                this.textBox1.Focus();                return false;            }            else if (this.textBox2.Text.Trim().Equals(string.Empty))            {                MessageBox.Show("请输入密码", CAPTION, MessageBoxButtons.OK, MessageBoxIcon.Information);                this.textBox2.Focus();                return false;            }            else if (this.comboBox1.Text.Trim().Equals(string.Empty))            {                MessageBox.Show("请输入密码", CAPTION, MessageBoxButtons.OK, MessageBoxIcon.Information);                this.comboBox1.Focus();                return false;            }            else            {                return true;            }        }        private void quxiao_Click(object sender, EventArgs e)        {            DialogResult result = MessageBox.Show("确认取消登录吗?", "操作提示", MessageBoxButtons.YesNo, MessageBoxIcon.Question);            if (result == DialogResult.Yes)            {                this.Close();            }        }        private void textBox2_TextChanged(object sender, EventArgs e)        {        }        private void textBox1_TextChanged(object sender, EventArgs e)        {        }        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)        {        }    }}