C# datagrideview插件的使用

  private void btnLogin_Click(object sender, EventArgs e)
         {
             string txtUserName = this.txtUserName.Text.Trim();
             string txtPwd = this.txtPwd.Text.Trim();
             if (txtUserName==null||txtPwd==null||txtUserName.Length==||txtPwd.Length==)
             {
                 MessageBox.Show("您输入的内容为空，请重新输入！");
             }
             string connString = "server=.;database=StudentMISDB;uid=sa;pwd=123456";
             SqlConnection conn = new SqlConnection(connString);
             conn.Open();
             string sql = @"select l.*,DATEDIFF(MI,LoginErrorLastTime,GETDATE()) as 间隔 from login as l where loginname='{0}'";
             sql = string.Format(sql, txtUserName);
             SqlCommand cmd = new SqlCommand(sql,conn);
             SqlDataAdapter adapter = new SqlDataAdapter(cmd);
             DataSet dSet = new DataSet();
             adapter.Fill(dSet);
             conn.Close();
             if (dSet.Tables[].Rows.Count > )
             {
                 int errorCount = Convert.ToInt32(dSet.Tables[].Rows[][]);
                 int times = Convert.ToInt32(dSet.Tables[].Rows[][]);
                 if (errorCount >=  && times <= )
                 {
                     if (dSet.Tables[].Rows[][].ToString() == txtUserName && dSet.Tables[].Rows[][].ToString()==txtPwd)
                     {
                         MessageBox.Show("登陆成功");
                         conn.Open();
                         string uptateSql = @"update login set loginerrorcount=0 where id='{0}'";
                         uptateSql = string.Format(uptateSql,dSet.Tables[].Rows[][].ToString());
                         cmd = new SqlCommand(uptateSql,conn);
                         cmd.ExecuteNonQuery();
                         conn.Close();
                     }
                     else
                     {
                         MessageBox.Show("登录名或者密码错误！");
                         conn.Open();
                         string updateSql = @"update login set loginerrorcount=loginerrorcount+1 ,loginerrorlasttime=getdate() where id='{0}'";
                         updateSql = string.Format(updateSql,dSet.Tables[].Rows[][].ToString());
                         cmd = new SqlCommand(updateSql,conn);
                         cmd.ExecuteNonQuery();
                         conn.Close();
                     }
                 }
                 else
                 {
                     MessageBox.Show("请在"+(-times)+"分钟后登录！");
                 }
             }
             else
             {
                 MessageBox.Show("用户不存在！");
             }
         }
     }

 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 ADO.NET8._30
 {
     public partial class DataGridView : Form
     {
         public DataGridView()
         {
             InitializeComponent();
         }

         private void DataGridView_Load(object sender, EventArgs e)
         {
             //加载学生选课信息
             loadStudntData();
             //加载课程信息（没有选的课程）
             LoadCourse();
         }
         /// <summary>
         /// 自定义一个方法
         /// </summary>
         private void LoadCourse()
         {
             //1.创建数据库连接符
             string connString = "server=.;database=StudentMISDB;uid=sa;pwd=123456";
             //2.链接数据库
             SqlConnection conn = new SqlConnection(connString);
             //3.添加数据库要执行的语句，通过ID查找没有选择到的课程
             string sql = @"select * from Course where CourseId not in(select distinct sc.CourseId from  [dbo].[Students] as s
                 join  Score as sc on s.StudentId=sc.StudentId
                 join  Course as c on sc.CourseId = c.CourseId
                 where s.StudentId='2')";
             //4.创建命令
             SqlCommand cmd = new SqlCommand(sql, conn);
             //5.断开式连接查询
             SqlDataAdapter da = new SqlDataAdapter(cmd);
             //6.创建数据缓冲区（数据集）
             DataSet ds = new DataSet();
             conn.Open();
             //7.填充数据集
             da.Fill(ds);
             conn.Close();
             //8.绑定数据源
             this.cmbCourseName.DataSource = ds.Tables[];

             //9.设置combobox控件中要显示的列
             //this.cmboxCourse.DisplayMember = "列名";
             this.cmbCourseName.DisplayMember = "Name";
             //10.DisplayMember绑定需要显示的数据表字段，而ValueMember绑定需要获取选择的项的值；直接可见的是此item的 DisplayMember 对应内容，而此 item的值是ValueMember 的对应内容。
             this.cmbCourseName.ValueMember = "CourseId";
         }
         /// <summary>
         /// 获取选中的值
         /// </summary>
         /// <param name="sender"></param>
         /// <param name="e"></param>
         private void cmbCourseName_SelectedIndexChanged(object sender, EventArgs e)
         {
             string courseID = this.cmbCourseName.SelectedValue.ToString();
             ///string courseName = this.cmboxCourse.SelectedText;
         }
         /// <summary>
         /// 保存 选课后，
         /// </summary>
         /// <param name="sender"></param>
         /// <param name="e"></param>
         private void btnSave_Click(object sender, EventArgs e)
         {
             //获取到在combobox控件中已经选择的值
             string courseID = this.cmbCourseName.SelectedValue.ToString();
             //string courseName = this.cmboxCourse.SelectedText;
             int studentId = ;
             //1.
             string connString = "server=.;database=StudentMISDB;uid=sa;pwd=123456";
             SqlConnection conn = new SqlConnection(connString);

             string sql = "insert into Score values('{0}','{1}','{2}')";
             sql = string.Format(sql, studentId, courseID, );

             SqlCommand cmd = new SqlCommand(sql, conn);
             conn.Open();
             int result = cmd.ExecuteNonQuery();
             conn.Close();
             if (result > )
             {
                 MessageBox.Show("保存成功");

                 loadStudntData();
                 LoadCourse();
             }
             else
             {
                 MessageBox.Show("保存失败");
             }
         }
         /// <summary>
         /// 加载学生选课信息
         /// </summary>
         private void loadStudntData()
         {
             string connString = "server=.;database=StudentMISDB;uid=sa;pwd=123456";
             SqlConnection conn = new SqlConnection(connString);

             string sql = @"select s.Studentid,c.courseId, s.Name as 姓名,c.Name as 课程名, sc.Score as 成绩 from  [dbo].[Students] as s
                 join  Score as sc on s.StudentId=sc.StudentId
                 join  Course as c on sc.CourseId = c.CourseId
                 where s.StudentId='{0}'";
             sql = string.Format(sql, );

             SqlCommand cmd = new SqlCommand(sql, conn);
             SqlDataAdapter da = new SqlDataAdapter(cmd);
             DataSet ds = new DataSet();
             conn.Open();
             da.Fill(ds);
             conn.Close();

             this.dataGridView1.DataSource = ds;
             this.dataGridView1.DataMember = ds.Tables[].TableName;
         }
     }
 }

二、（1）封装的类：

 using System;
 using System.Collections.Generic;
 using System.Data.SqlClient;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using System.Data;

 namespace Demo2
 {
 public static    class SqlCommon
     {

         /// <summary>
         /// 连接字符串
         /// </summary>
         public static string connString = "server=.;database=StudentMISDB;uid=sa;pwd=123456";

         /// <summary>
         /// 执行增删改操作
         /// </summary>
         /// <param name="sql">sql语句 参数传入</param>
         /// <returns></returns>
         public static int ExecuteSql(string sql)
         {
             int result = ;
             //创建连接对象new SqlConnection( 连接字符串)
             SqlConnection conn = new SqlConnection(connString);
             //创建命令对象  new SqlCommand(sql语句, conn)
             SqlCommand cmd = new SqlCommand(sql, conn);
             // 打开数据连接
             conn.Open();
             // 执行 sql 命令，返回受影响的行数
             result = cmd.ExecuteNonQuery();
             // 关闭数据连接
             conn.Close();
             // 把执行结果【受影响的行数】，返回给调用者
             return result;
         }

         public static DataSet ExecuteQuery(string sql) {

             SqlConnection conn = new SqlConnection(connString);
             SqlCommand cmd = new SqlCommand(sql, conn);
             SqlDataAdapter da = new SqlDataAdapter(cmd);
             DataSet ds = new DataSet();
             conn.Open();
             da.Fill(ds);
             conn.Close();

             return ds;
         }
     }
 }

（二）、调用类

 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 Demo2
 {
     public partial class Form1 : Form
     {
         public Form1()
         {
             InitializeComponent();
         }

         private void btnAdd_Click(object sender, EventArgs e)
         {
             /// 定义变量接收  用户输入的值
             string loginName = this.txtLoginName.Text.Trim();
             string pwd = this.txtPWD.Text.Trim();

             ///判断用户是否有输入值
             if (loginName == "" || loginName == null)
             {
                 MessageBox.Show("请输入用户名");
                 return;
             }
             //string.IsNullOrEmpty(字符串) ==>判断字符串是否为“空字符”或为 null
             if (string.IsNullOrEmpty(pwd))
             {
                 MessageBox.Show("请输入密码");
                 return;
             }

             if (isExistsLoginName(loginName))
             {
                 MessageBox.Show("该用户名已经存在，请重新输入");
                 this.txtLoginName.Text = string.Empty;
                 this.txtPWD.Text = string.Empty;
                 return;
             }

             string sql = @"insert  into LoginInfo (loginName,pwd,LoginErrorLastTime)
             values('{0}','{1}','{2}')";
             sql = string.Format(sql, loginName, pwd, DateTime.Now.ToString());

             int row = SqlCommon.ExecuteSql(sql);
             if (row > )
             {
                 MessageBox.Show("添加成功");
             }
             else
             {
                 MessageBox.Show("添加失败");
             }

         }

         #region 判断 用户名是否存在

         private bool isExistsLoginName(string loginName)
         {
             string sql = @"select * from LoginInfo where LoginName='{0}'";
             sql = string.Format(sql, loginName);
             DataSet ds = SqlCommon.ExecuteQuery(sql);
             return ds.Tables[].Rows.Count > ;
         }
         #endregion
     }
 }

（三）、datagrideview插件

 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 Demo2
 {
     public partial class FrmScore : Form
     {
         public FrmScore()
         {
             InitializeComponent();
         }

         private void btnSelect_Click(object sender, EventArgs e)
         {
             string name = this.txtCourse.Text.Trim();

             string sql = @"select ScoreId,Name,Score from Course as c
             join Score as sc on c.CourseId = sc.CourseId
             where sc.StudentId='1' and c.Name like '%{0}%'";
             sql = string.Format(sql,name);
             DataSet ds = SqlCommon.ExecuteQuery(sql);

             this.dataGridView1.DataSource = ds.Tables[];

         }
     }
 }