2章 上级1-3 关键代码

using System;
using System.Collections.Generic;
using System.Text;
using System.Data.SqlClient;
using System.Data;
using System.Threading.Tasks;
using System.Linq;
namespace WindowsFormsApplication1
{
/// <summary>
/// 此类维护数据库连接字符串，和 Connection 对象
/// </summary>
public  class DBHelper
{
// 数据库连接字符串
private string connString = @"Data Source=.;Initial Catalog=MySchool;Integrated Security=True";

// 数据库连接 Connection 对象
private SqlConnection connection;

/// <summary>
/// Connection对象
/// </summary>
public SqlConnection Connection
{
get
{
if (connection == null)
{
connection = new SqlConnection(connString);
}
return connection;
}
}

/// <summary>
/// 打开数据库连接
/// </summary>
public void OpenConnection()
{
if (Connection.State == ConnectionState.Closed)
{
Connection.Open();
}
else if (Connection.State == ConnectionState.Broken)
{
Connection.Close();
Connection.Open();
}
}

/// <summary>
/// 关闭数据库连接
/// </summary>
public void CloseConnection()
{
if (Connection.State == ConnectionState.Open || Connection.State == ConnectionState.Broken)
{
Connection.Close();
}
}
}
}

namespace WindowsFormsApplication1
{

public partial class Form4 : Form
{

public Form4()
{
InitializeComponent();
}

private void button1_Click(object sender, EventArgs e)
{
this.Close();
}

private void Form4_Load(object sender, EventArgs e)
{
MessageBox.Show("系统发生错误", "提示", MessageBoxButtons.OK, MessageBoxIcon.);
BindGrade();

}

private void nianji_SelectedIndexChanged(object sender, EventArgs e)
{

}
public bool BindGrade() {
DBHelper db = new DBHelper();
try
{
string sql = "SELECT * FROM [Grade]";
db.OpenConnection();
SqlCommand comm = new SqlCommand(sql, db.Connection);
SqlDataReader m = comm.ExecuteReader();
while (m.Read())
{
string g = m["GradeName"].ToString();
nianji.Items.Add(g);
}
m.Close();

return false;
}
catch (Exception e)
{
Console.WriteLine(e);
MessageBox.Show("系统发生错误", "提示", MessageBoxButtons.OK, MessageBoxIcon.Warning);
return false;
}
finally {
db.CloseConnection();
}
}
}

}

namespace WindowsFormsApplication1
{
public partial class Form3 : Form
{
public Form3()
{
InitializeComponent();
}

private void toolStripButton1_Click(object sender, EventArgs e)
{
Form4 s = new Form4();
s.MdiParent = this;
s.Show();
}

private void 退出ToolStripMenuItem_Click(object sender, EventArgs e)
{
this.Close();
}

private void button1_Click(object sender, EventArgs e)
{
this.Close();
}
}
}