C#深入.NET平台的软件系统分层开发

今天我们来讲讲分层开发，你从标题能不能简单的认识一下什么是分层呢？

不懂也没关系，接下来我来给你讲讲。

第一章 软件系统的分层开发

（1）其实分层模式可以这样定义：将解决方案中功能不同的模块分到不同的项目中实现，每一层中的组件应保持内聚性，每一层都应该与它下面的各层保持松耦合。

       分层模式是最常见的一种架构模式，甚至可以说分层模式是很多架构模式的基础。

       数据访问层：

          这一层处于最底层，负责与数据库的交互，也成为DAL（Data Access Layer）

       表示层：

         这一层直接与用户打交道，负责显示或者获取数据，也称为UI（User Interface Layer）

（2）.NET程序集是任何.NET Framework应用程序的基本构造块。程序集由描述它的程序集清单（包含版本号，程序集名称等），类型元数据，MSIL代码和资源组成，

        这些部分都分布在一个文件中。

        程序集主要包括以下两类：

        （1）可执行文件，即.exe文件   （2）类库文件，即.dll文件

（3）程序集，解决方案，项目和命名空间的关系如下：

        （1）一个解决方案可以由一个或者多个项目组成，这些项目可以是Windows应用程序，类库等。

        （2）一个程序集可以包含多个命名空间，程序集默认的命名空间名称就是程序集的名称。

        （3）命名空间是组织C#程序的一种逻辑架构，一个命名空间可以有多个类。

（4）分层开发的优点：

       （1）代码的复用（2）分离开发人员的关注（3）无损提换（4）降低了系统间的依赖

（5）异常处理

   常见的异常类型:

      System.Exception :这个类提供系统异常和应用程序异常之间的区别

      System.SQLException :当SQL Server返回警告或者错误时引发的异常

      ArgumentNullException :当将空引用传递给不接受它作为有效参数的方法时引发的异常

      FileNotFoundException :试图访问磁盘上不存在的文件失败时引发的异常

      IOException :当出现I/O错误时，引发此异常

      ApplicationException :在应用程序执行过程中检测到由应用程序定义的异常

  异常类的常用属性：

     Message :提供引起异常的详细信息

     Source :表示导致异常发生的应用程序或者对象的名称

     StackTrace :提供在栈堆上所调用方法的详细信息，并首先显示最近调用的方法

     InnerException :对内部异常的引用，如果此异常基于前一个异常，则内部异常指最初发生的异常

（6）异常处理回顾

    语法：

try-catch
 try
{
  //可能引发异常的工作代码
}
catch(异常对象)
{
 //异常处理
}

try-finally
 try
{
 //可能引发异常的工作代码
}
finally
{
 //清理相关对象的代码
}

try-catch-finally
 try
{
//可能引发异常的工作代码
}
catch(异常对象)
{
 //异常处理
}
finally
{
 //清理相关对象的代码
}

上面的文字都是枯燥的，接下来用代码来演示一下：

  /// <summary>
    /// 数据访问层
    /// </summary>
   public  class StudentDAL
    {

        public  void AddStudent()
        {

        }

        public DataTable SelectStudent()
        {
            string str = "Data Source=.; initial catalog=MySchools;user id=sa;";
            string sql = "select * from student ";
            SqlConnection con = new SqlConnection(str);
            SqlDataAdapter da = new SqlDataAdapter(sql,con);
            DataSet ds = new DataSet();

            try
            {
                //int num = 0;
                //int result = 1 / num;
                da.Fill(ds, "stuInfo");
                return ds.Tables["stuInfo"];
            }
            catch (SqlException ex)
            {

                throw new Exception("访问数据库失败" + ex.Message);
            }
            catch (DivideByZeroException ex)
            {

                throw new Exception("除数不能为0" + ex.Message);
            }
            catch (Exception ex)
            {

                throw new Exception("失败" + ex.Message);
            }

        }

 /// <summary>
    /// 数据访问层
    /// </summary>
   public class GradeDAL
    {
        public DataTable SelectGrade()
        {
            string str = "data source=.; initial catalog=MySchools; user id=sa;";
            string sql = "select * from Grade";
            SqlConnection con = new SqlConnection(str);
            SqlDataAdapter da = new SqlDataAdapter(sql,con);
            DataSet ds = new DataSet();
            da.Fill(ds,"gradeInfo");

            return ds.Tables["gradeInfo"];
        }
    }

 private void Form1_Load(object sender, EventArgs e)
        {
            StudentDAL dal = new StudentDAL();
            GradeDAL grade = new GradeDAL();
            try
            {
               DataTable data = dal.SelectStudent();
               DataTable table = grade.SelectGrade();
               dgvList.DataSource = data;

                comboBox1.DataSource = grade.SelectGrade();
                comboBox1.DisplayMember = "GradeName";
                comboBox1.ValueMember = "GradeId";
            }
            catch (Exception ex)
            {

                MessageBox.Show(ex.Message);
            }

        }

第二章 OOP典型应用：实体类

（1）实体类是业务对象的基础，它用面向对象的思想消除了关系数据与对象之间的差异

   实体类:

/// <summary>
    /// 部门表
    /// </summary>
    public class Department
    {
        public int BId { get; set; }
        public int BName{ get; set; }

    }

 /// <summary>
    /// 员工表
    /// </summary>
    public class Employee
    {
        public int YId{ get; set; }
        public int YName{ get; set; }
        public int BId{ get; set; }
        public int ZId{ get; set; }
    }

 /// <summary>
    /// 任务内容表
    /// </summary>
    public class Task
    {
        public string Contents {get;set;}
        public int RId {get;set;}
        public int YId {get;set;}
        public DateTime Time {get;set;}
        public int Hours {get;set;}
        public string Type { get; set; }
    }

数据访问层：

public  class InfoAddDAL
    {

        public bool Add(string name)
        {
            bool falg = false;
            string sql = "insert into ProgramInfo(pname) values('"+name+"')";
            int num=SQLHelper.ExecuteNonQuery(sql);
            if(num==)
            {
                falg= true;
            }
            return falg;
        }

        public DataTable SelectInfo()
        {
            List<string> list = new List<string>();

            try
            {
                string sql = "select pname from ProgramInfo";
                DataTable table=SQLHelper.ExecuteDataTable(sql);
                return table;

            }
            catch (SqlException ex)
            {

                throw ex;
            }
            catch(Exception ex)
            {
                throw ex;
            }
        }

        public bool DeleteInfo(string name)
        {
            bool falg = false;
            try
            {
                string sql = "delete ProgramInfo where pname='" + name + "'";
                int num=SQLHelper.ExecuteNonQuery(sql);
                if (num == )
                {
                    falg= true;
                }
                return falg;
            }
            catch (SqlException ex)
            {

                throw ex;
            }
            catch(Exception ex)
            {
                throw ex;

            }

        }

        public bool UpdateInfo(string name,string names)
        {
            bool falg = false;
            string sql = "Update  ProgramInfo set pname='"+name+"'where pname='"+names+"'";
            int num=SQLHelper.ExecuteNonQuery(sql);
            if(num==)
            {
                falg= true;
            }
            return falg;
        }
    }

接下来是一个辅助类，因为以后要经常用，有能力的自己写一个工具吧！

 public static  class SQLHelper
    {
      //用静态的方法调用的时候不用创建SQLHelper的实例
      //Execetenonquery
     // public static string Constr = "server=HAPPYPIG\\SQLMODEL;database=shooltest;uid=sa;pwd=6375196;";
      public static string Constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
      public static int id;
      /// <summary>
      /// 执行NonQuery命令
      /// </summary>
      /// <param name="cmdTxt"></param>
      /// <param name="parames"></param>
      /// <returns></returns>
      public static int ExecuteNonQuery(string cmdTxt, params SqlParameter[] parames)
      {
          return ExecuteNonQuery(cmdTxt, CommandType.Text, parames);
      }
      //可以使用存储过程的ExecuteNonquery
      public static int ExecuteNonQuery(string cmdTxt, CommandType cmdtype, params SqlParameter[] parames)
      {
          //判断脚本是否为空 ，直接返回0
          if (string.IsNullOrEmpty(cmdTxt))
          {
              return ;
          }
          using (SqlConnection con = new SqlConnection(Constr))
          {
              using (SqlCommand cmd = new SqlCommand(cmdTxt, con))
              {
                  if (parames != null)
                  {
                      cmd.CommandType = cmdtype;
                      cmd.Parameters.AddRange(parames);
                  }
                  con.Open();
                  return cmd.ExecuteNonQuery();
              }
          }
      }
      public static SqlDataReader ExecuteDataReader(string cmdTxt, params SqlParameter[] parames)
      {
          return ExecuteDataReader(cmdTxt, CommandType.Text, parames);
      }
      //SQLDataReader存储过程方法
      public static SqlDataReader ExecuteDataReader(string cmdTxt, CommandType cmdtype, params SqlParameter[] parames)
      {
          if (string.IsNullOrEmpty(cmdTxt))
          {
              return null;
          }
          SqlConnection con = new SqlConnection(Constr);

          using (SqlCommand cmd = new SqlCommand(cmdTxt, con))
          {
              cmd.CommandType = cmdtype;
              if (parames != null)
              {

                  cmd.Parameters.AddRange(parames);
              }
              con.Open();
              //把reader的行为加进来。当reader释放资源的时候，con也被一块关闭
              return cmd.ExecuteReader(System.Data.CommandBehavior.CloseConnection);
          }

      }
      public static DataTable ExecuteDataTable(string sql, params SqlParameter[] parames)
      {
          return ExecuteDataTable(sql, CommandType.Text, parames);
      }
      //调用存储过程的类，关于(ExecuteDataTable)
      public static DataTable ExecuteDataTable(string sql, CommandType cmdType, params SqlParameter[] parames)
      {
          if (string.IsNullOrEmpty(sql))
          {
              return null;
          }
          DataTable dt = new DataTable();
          using (SqlDataAdapter da = new SqlDataAdapter(sql, Constr))
          {
              da.SelectCommand.CommandType = cmdType;
              if (parames != null)
              {
                  da.SelectCommand.Parameters.AddRange(parames);
              }
              da.Fill(dt);
              return dt;
          }
      }

      /// <summary>
      /// ExecuteScalar
      /// </summary>
      /// <param name="cmdTxt">第一个参数，SQLServer语句</param>
      /// <param name="parames">第二个参数，传递0个或者多个参数</param>
      /// <returns></returns>
      public static object ExecuteScalar(string cmdTxt, params SqlParameter[] parames)
      {
          return ExecuteScalar(cmdTxt, CommandType.Text, parames);
      }
      //可使用存储过程的ExecuteScalar
      public static object ExecuteScalar(string cmdTxt, CommandType cmdtype, params SqlParameter[] parames)
      {
          if (string.IsNullOrEmpty(cmdTxt))
          {
              return null;
          }
          using (SqlConnection con = new SqlConnection(Constr))
          {
              using (SqlCommand cmd = new SqlCommand(cmdTxt, con))
              {
                  cmd.CommandType = cmdtype;
                  if (parames != null)
                  {
                      cmd.Parameters.AddRange(parames);
                  }
                  con.Open();
                return   cmd.ExecuteScalar();
              }
          }

      }
      //调用存储过程的DBHelper类（关于ExeceutScalar,包含事务,只能处理Int类型，返回错误号）
      public static object ExecuteScalar(string cmdTxt, CommandType cmdtype,SqlTransaction sqltran, params SqlParameter[] parames)
      {
           if (string.IsNullOrEmpty(cmdTxt))
          {
              return ;
          }
          using (SqlConnection con = new SqlConnection(Constr))
          {
              int sum = ;
              using (SqlCommand cmd = new SqlCommand(cmdTxt, con))
              {
                  cmd.CommandType=cmdtype;
                  if (parames != null)
                  {
                      cmd.Parameters.AddRange(parames);
                  }
                  con.Open();
                  sqltran = con.BeginTransaction();
                  try
                  {
                      cmd.Transaction = sqltran;
                      sum=Convert.ToInt32( cmd.ExecuteScalar());
                      sqltran.Commit();
                  }
                  catch (SqlException ex)
                  {
                      sqltran.Rollback();
                  }
                  return sum;
              }
          }
      }
    }

数据访问层：

 public class TaskDAL
    {
        //查询信息
        public DataTable Info()
        {
            string sql = "select Contents,YName,  Time, Hours, Type from Task,Employee where Task.YId=Employee.YId";
            DataTable table =SQLHelper.ExecuteDataTable(sql);
            return table;
        }

        public DataTable RSelectInfo(Task task)
        {
            string sql = "select Contents,YName,  Time, Hours, Type from Task,Employee where Task.YId=Employee.YId and Contents='"+task.Contents+"'";
            DataTable table = SQLHelper.ExecuteDataTable(sql);
            return table;
        }
        //根据条件查询
        public DataTable SelectInfo(DateTime time1, DateTime time2)
        {
            string sql = "select Contents,YName,  Time, Hours, Type from Task,Employee where Time between'" + time1 + "' and '"+ time2 + "' and Task.YId=Employee.YId";
            DataTable table = SQLHelper.ExecuteDataTable(sql);
            return table;
        }

        //加载任务名称
        public DataTable RInfo()
        {
            string sql = "select Contents from Task ";
            DataTable table = SQLHelper.ExecuteDataTable(sql);

            return table;
        }
    }

在这里再引用一个App.config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <connectionStrings>
    <add name="constr" connectionString="data source=.; initial catalog=AddInfo; uid=sa;">
    </add>
  </connectionStrings>
    <startup>
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5.2" />
    </startup>
</configuration>

窗体加载：

  private void FrmMain_Load(object sender, EventArgs e)
        {
            txt02.Enabled = false;
        }

        private void btn01_Click(object sender, EventArgs e)
        {
            InfoAddDAL info = new InfoAddDAL();
            if (txt02.Text=="")
            {
                MessageBox.Show("请输入你要添加的文本");
           }
            else
            {
                try
                {
                    bool falg = info.Add(txt02.Text);
                    if (falg)
                    {
                        DataTable table = info.SelectInfo();
                        lb01.DataSource = table;
                        lb01.DisplayMember = "pname";
                    }
                    txt02.Text = "";
                }
                catch (SqlException)
                {

                    MessageBox.Show("sql语句错误");
                }
                catch (Exception)
                {
                    MessageBox.Show("程序出错");
                }
            }

        }

        private void btn02_Click(object sender, EventArgs e)
        {
            InfoAddDAL info = new InfoAddDAL();
            string name = lb01.SelectedItem.ToString();
            bool falg = info.DeleteInfo(name);
           if (falg)
           {
              DataTable table = info.SelectInfo();
              lb01.DataSource = table;
              lb01.DisplayMember = "pname";
           }

        }

        private void lb01_DoubleClick(object sender, EventArgs e)
        {

            string name = lb01.SelectedItem.ToString();
            txt02.Text = name;
        }

        private void btn03_Click(object sender, EventArgs e)
        {
            if(txt02.Text=="")
            {
                MessageBox.Show("请选择要修改的文本");
            }
            else
            {
                string name = lb01.SelectedItem.ToString();
                InfoAddDAL info = new InfoAddDAL();
                bool falg = info.UpdateInfo(txt02.Text, name);
                if (falg)
                {
                    DataTable table = info.SelectInfo();
                    lb01.DataSource = table;
                    lb01.DisplayMember = "pname";
                }
                txt02.Text = "";
            }

        }

        private void btn04_Click(object sender, EventArgs e)
        {
            txt02.Enabled = true;
            InfoAddDAL info = new InfoAddDAL();
            try
            {
                DataTable table = info.SelectInfo();
                lb01.DataSource = table;
                lb01.DisplayMember = "pname";
            }
            catch (SqlException)
            {

                MessageBox.Show("sql语句错误");
            }
            catch (Exception)
            {
                MessageBox.Show("程序出错");
            }

        }
    }

    TaskDAL DAL = new TaskDAL();
        DataTable table = null;

        private void btn01_Click(object sender, EventArgs e)
        {

            DateTime time1 = dateTimePicker1.Value;
            DateTime time2 = dtp02.Value;
            if (cbo01.Text == "")
            {
                table = DAL.Info();
            }
            else if(time1.ToString() != "" && time2.ToString() != "")
            {
                table = DAL.SelectInfo(time1, time2);
            }
            else if(cbo01.Text!=""&& time1.ToString() != "" && time2.ToString() != "")
            {
                Task task = new Task();
                task.Contents = cbo01.SelectedText.ToString();
                table = DAL.RSelectInfo(task);
            }
            dgvList.DataSource = table;
        }

        private void FrmTwo_Load(object sender, EventArgs e)
        {
            table= DAL.RInfo();
            cbo01.DisplayMember = "Contents";
            cbo01.DataSource = table;
        }

配置文件里保存的是应用程序运行所依赖的常量，这些常量可能会随着多种因素的变化而变化，所以将这些信息写在配置文件中，由程序来动态读取。
读取连接字符串的语法如下：

 public static readonly string conString=ConfigurationManager.ConnectionStrings["MySchoolConnectionString"].ToString();

（2）const和readonly的区别

   （1）readonly只能修饰类变量   const修饰成员变量和局部变量

   （2）readonly在运行时赋值，const在编译时赋值

   （3）const只能修饰值类型和特殊的引用类型  readonly可以修饰任何类型

第三章 提高系统性能：从数据访问开始

（1）using语句

       using的作用：（1）导入命名空间（2）释放实现了disposable接口的对象非托管资源

       语法：

       using(SqlConnection con=new SqlConnection(constr))

        {

           //数据库操作代码.......

         }

（2）参数化命令（防止SQL注入攻击）

   语法：

（）使用参数名和参数类型进行设置

           public SqlParameter Add(string parameterName,SqlDbType slDbType);

           public SqlParameter Add(string parameterName,SqlDbType paraValue,int size);

（）使用SqlParameter对象进行填充

           public SqlParameter Add(SqlParameter  value);  //添加单个参数

           public void AddRange(SqlParameter[]  values);  //添加多个参数

    （3）SqlParameter类的常用属性

DbType :获取或设置参数的DbType

        Direction :获取或设置一个值，该值表示参数是只可输入，是可输出，还是双向存储过程返回值参数

        IsNullable :获取或设置一个值，该值指示参数是否接受空值

        ParameterName :获取或设置SqlParameter的名称

        Size :获取或设置列中数据的最大值（以字节为单位）

        SqlDbType :获取或设置参数的SqlDbType

        Value ：获取或设置该参数的值

第四章 业务的扩展：三层架构

（1）业务逻辑层BLL（Business Logic Layer）

实体类：

public class Grade
    {
        public int GradeId { get; set; }
        public string GradeName { get;set;}

    }

 public class Result
    {
        public int StudentNo { get; set; }
        public int SubjectId { get; set; }
        public int StudentResult { get; set; }
        public string ExamDate { get; set; }
        public int Id { get; set; }
    }

public class Student
    {
        public int StudentNo { get; set; }
        public string StudentName { get; set; }
        public string LoginPwd { get; set; }
        public int GradeId { get; set; }
        public string Gender { get; set; }
        public string Address { get; set; }
        public string Phone { get; set; }
        public DateTime Birthday { get; set; }
        public string Email { get; set; }
        public string IdentityId { get; set; }
    }

public class Subject
    {
        public int SubjectId { get; set; }
        public string SubjectName { get; set; }
        public int ClassHour { get; set; }
        public int GradeId { get; set; }
    }

数据访问层DAL：

 /// <summary>
    /// 班级表
    /// </summary>
   public  class GradeDAL
    {
        //加载班级信息
        public DataTable GradeInfo()
        {
            string sql = "select * from Grade";
            DataTable table=SQLHelper.ExecuteDataTable(sql);
            return table;
        }
    }

  public class MyTool
    {
        /// <summary>
        /// DataSetToList
        /// </summary>
        /// <typeparam name="T">转换类型</typeparam>
        /// <param name="dataSet">数据源</param>
        /// <param name="tableIndex">需要转换表的索引</param>
        /// <returns></returns>
        public List<T> DataTableToList<T>(DataTable dt)
        {
            //确认参数有效
            if (dt == null )
                return null;
            List<T> list = new List<T>();

            for (int i = ; i < dt.Rows.Count; i++)
            {
                //创建泛型对象
                T _t = Activator.CreateInstance<T>();
                //获取对象所有属性
                PropertyInfo[] propertyInfo = _t.GetType().GetProperties();
                for (int j = ; j < dt.Columns.Count; j++)
                {
                    foreach (PropertyInfo info in propertyInfo)
                    {
                        //属性名称和列名相同时赋值
                        if (dt.Columns[j].ColumnName.ToUpper().Equals(info.Name.ToUpper()))
                        {
                            if (dt.Rows[i][j] != DBNull.Value)
                            {
                                info.SetValue(_t, dt.Rows[i][j], null);
                            }
                            else
                            {
                                info.SetValue(_t, null, null);
                            }
                            break;
                        }
                    }
                }
                list.Add(_t);
            }
            return list;
        }
    }

 /// <summary>
    ///  成绩表
    /// </summary>
   public  class ResultDAL
    {
        //根据科目条件查询成绩
        public DataTable SelectResult(int subjectid)
        {
            string sql = "select StudentName,SubjectName,StudentResult,ExamDate,student.studentno from student,subject,result where Subject.subjectid=result.subjectid and student.StudentNo=Result.StudentNo and result.subjectid="+subjectid+" ";
            DataTable table = SQLHelper.ExecuteDataTable(sql);
            return table;
        }
        //根据姓名查询成绩
        public DataTable SelectResult(string studentname)
        {
            string sql = "select StudentName,SubjectName,StudentResult,ExamDate,student.studentno from student,subject,result where student.studentName like'%" + studentname + "%' and Subject.subjectid=result.subjectid and student.StudentNo=Result.StudentNo  ";
            DataTable table= SQLHelper.ExecuteDataTable(sql);
            return table;
        }
        //查询全部成绩
        public DataTable SelectResult()
        {
            string sql = "select StudentName,SubjectName,StudentResult,ExamDate,student.studentno from student,subject,result where Subject.subjectid=result.subjectid and student.StudentNo=Result.StudentNo  ";
            DataTable table = SQLHelper.ExecuteDataTable(sql);
            return table;
        }
       // 修改学生成绩
        public bool UpdateResult(Result result)
        {
            bool flag = false;
            string sql = "update Result set StudentResult='" + result.StudentResult+ "',ExamDate='"+result.ExamDate+ "',SubjectId='"+result.SubjectId+"' where result.studentno="+result.StudentNo+"";
           int count= SQLHelper.ExecuteNonQuery(sql);
            if(count>)
            {
                flag = true;
            }
            return flag;
        }
        //添加学生成绩
        public bool AddResult(Result result)
        {
            bool flag = false;
            string sql = "insert into result values(@studentno,@subjectid,@studentresult,@examdate)";
            SqlParameter[] para =
            {
                new SqlParameter("@studentno",result.StudentNo),
                new SqlParameter("@subjectid",result.SubjectId),
                new SqlParameter("@studentresult",result.StudentResult),
                new SqlParameter("@examdate",result.ExamDate)
            };
            int num=Convert.ToInt32(SQLHelper.ExecuteScalar(sql,para));
            if(num>)
            {
                flag = true;
            }
            return flag;
        }
    }

/// <summary>
    /// 学生表
    /// </summary>
    public class StudentDAL
    {
        //Login登录
        public bool IsLogin(Student stu)
        {
            #region 方式一：登录
            //bool flag = false;
            //string sql = "select count(1) from student where studentno=" + stu.StudentNo + " and Loginpwd='" + stu.LoginPwd + "'";
            //int count = Convert.ToInt32(SQLHelper.ExecuteScalar(sql));
            //if (count > 0)
            //{
            //    flag = true;
            //}
            //return flag;
            #endregion
            #region 方式二：登录
            bool flag = false;
            string sql = "select count(1) from student where studentno=@studentno and loginpwd=@pwd";
            SqlParameter[] para =
             {
                new SqlParameter("@studentno",stu.StudentNo),
                new SqlParameter("@pwd",stu.LoginPwd)
            };
            int count = Convert.ToInt32(SQLHelper.ExecuteScalar(sql, para));
            if (count > )
            {
                flag = true;
            }
            return flag;
            #endregion
        }
        //根据条件学生信息
        // StudentNo, LoginPwd, StudentName, Gender, GradeId, Phone, Address, Birthday, Email,
        public List<Student> StudentInfo(int gradeid)
        {
            #region 查询一
            List<Student> list = new List<Student>();
            string sql = "select StudentNo, LoginPwd, StudentName, Gender, GradeId, Phone, Address, Birthday, Email,IdentityId from student where GradeId=" + gradeid + "";
            SqlDataReader dr = SQLHelper.ExecuteDataReader(sql);
            if (dr.HasRows)
            {
                while (dr.Read())
                {
                    Student stu = new Student();
                    stu.StudentNo = Convert.ToInt32(dr["StudentNo"]);
                    stu.LoginPwd = dr["LoginPwd"].ToString();
                    stu.StudentName = dr["StudentName"].ToString();
                    stu.Gender = dr["Gender"].ToString();
                    stu.GradeId = Convert.ToInt32(dr["GradeId"]);
                    stu.Phone = dr["Phone"].ToString();
                    stu.Address = dr["Address"].ToString();
                    stu.Birthday = Convert.ToDateTime(dr["Birthday"]);
                    stu.Email = dr["Email"].ToString();
                    stu.IdentityId = dr["IdentityId"].ToString();
                    list.Add(stu);
                }
            }
            dr.Close();
            return list;
            #endregion

        }
        public List<Student> StudentInfo(string name)
        {
            #region 查询一
            List<Student> list = new List<Student>();
            string sql = "select StudentNo, LoginPwd, StudentName, Gender, GradeId, Phone, Address, Birthday, Email,IdentityId from student where StudentName=" + name + "";
            SqlDataReader dr = SQLHelper.ExecuteDataReader(sql);
            if (dr.HasRows)
            {
                while (dr.Read())
                {
                    Student stu = new Student();
                    stu.StudentNo = Convert.ToInt32(dr["StudentNo"]);
                    stu.LoginPwd = dr["LoginPwd"].ToString();
                    stu.StudentName = dr["StudentName"].ToString();
                    stu.Gender = dr["Gender"].ToString();
                    stu.GradeId = Convert.ToInt32(dr["GradeId"]);
                    stu.Phone = dr["Phone"].ToString();
                    stu.Address = dr["Address"].ToString();
                    stu.Birthday = Convert.ToDateTime(dr["Birthday"]);
                    stu.Email = dr["Email"].ToString();
                    stu.IdentityId = dr["IdentityId"].ToString();
                    list.Add(stu);
                }
            }
            dr.Close();
            return list;
            #endregion

        }
        // 添加学生信息
        public int StudentAdd(Student stu)
        {

            string sql = "insert into student values('" + stu.LoginPwd + "','" + stu.StudentName + "'," + stu.Gender + ",'" + stu.GradeId + "','" + stu.Phone + "','" + stu.Address + "','" + stu.Birthday + "','" + stu.Email + "','"+stu.IdentityId+"');select @@IDENTITY";

            int num = Convert.ToInt32(SQLHelper.ExecuteScalar(sql));

            return num;

        }
        //修改学生信息
        public bool UpdateInfo(Student stu)
        {
            bool flag = false;
            string str = "data source=.; initial catalog=MySchool; uid=sa;";
            using (SqlConnection con = new SqlConnection(str))
            {
                SqlCommand com = con.CreateCommand();
                com.CommandText = "usp_Update";
                com.CommandType = CommandType.StoredProcedure;
                SqlParameter[] para =
                {
                new SqlParameter("@studentno",stu.StudentNo),
                new SqlParameter("@pwd",stu.LoginPwd),
                new SqlParameter("@name",stu.StudentName),
                new SqlParameter("@gender",stu.Gender),
                new SqlParameter("@gradeid",stu.GradeId),
                new SqlParameter("@phone",stu.Phone),
                new SqlParameter("@address",stu.Address),
                new SqlParameter("@birthday",stu.Birthday),
                new SqlParameter("@email",stu.Email),
                new SqlParameter("@identitycard",stu.IdentityId)
            };
                com.Parameters.AddRange(para);
                con.Open();
                int count = com.ExecuteNonQuery();
                if (count > )
                {
                    flag = true;
                }
                return flag;
            }

        }
        //查询全部学生信息
        public DataTable Student()
        {
            string sql = "select StudentNo, LoginPwd, StudentName, Gender, GradeName, Phone, Address, Birthday, Email,IdentityCard from student,grade where student.gradeid=grade.gradeid";
            DataTable table = SQLHelper.ExecuteDataTable(sql);
            return table;
        }
        //条件查询学生信息
        public DataTable Student(string name)
        {
            string sql = "select StudentNo, LoginPwd, StudentName, Gender, GradeId, Phone, Address, Birthday, Email,IdentityCard from student,grade where gradename=@name and student.gradeid=grade.gradeid";
            SqlParameter para = new SqlParameter("@name", name);
            DataTable table = SQLHelper.ExecuteDataTable(sql, para);
            return table;
        }
        public DataTable SelectStudent(string gradename,string grader)
        {
            string sql = "select StudentNo, LoginPwd, StudentName, Gender,student.Gradeid, Phone, Address, Birthday, Email,IdentityCard from student,grade where student.gradeid=grade.gradeid and gradename=@name and gender=@gender";
            SqlParameter[] para =
            {
                 new SqlParameter("@name",gradename),
                 new SqlParameter("@gender",grader)
             };
            DataTable table = SQLHelper.ExecuteDataTable(sql, para);
            return table;
        }
        public DataTable SelectStudent(string gradename)
        {
            string sql = "select StudentNo, LoginPwd, StudentName, Gender,student.GradeId, Phone, Address, Birthday, Email,IdentityCard from student,grade where student.gradeid=grade.gradeid and gradename=@name";
            SqlParameter para = new SqlParameter("@name",gradename);
            DataTable table = SQLHelper.ExecuteDataTable(sql, para);
            return table;
        }
    }

 /// <summary>
    /// 科目表
    /// </summary>
    public class SubjectDAL
    {
        public DataTable SubjectInfo()
        {
            string sql = "select * from subject";
            DataTable table = SQLHelper.ExecuteDataTable(sql);
            return table;
        }

        public List<Subject> SubjectALL(int gradeid)
        {
            string sql = "select * from subject where gradeid=@gradeid";
            SqlParameter para = new SqlParameter("@gradeid",gradeid);
            DataTable table = SQLHelper.ExecuteDataTable(sql,para);
            MyTool tool = new MyTool();
            List<Subject>  list=tool.DataTableToList<Subject>(table);
            return list;
        }
    }

业务逻辑层BLL：

 public class GradeBLL
    {
        GradeDAL dal = new GradeDAL();
        //加载年级信息
        public DataTable GradeInfo()
        {
            return dal.GradeInfo();
        }
    }

public class ResultBLL
    {
        ResultDAL dal = new ResultDAL();
        public DataTable SelectResult(int subjectid)
        {
            return dal.SelectResult(subjectid);
        }
        //条件查询
        public DataTable SelectResult(string studentname)
        {
            return dal.SelectResult(studentname);
        }
        //查询全部
        public DataTable SelectResult()
        {
            return dal.SelectResult();
        }
        //修改成绩
        public bool UpdateResult(Result result)
        {
            return dal.UpdateResult(result);
        }
        //添加学生成绩
        public bool AddResult(Result result)
        {
            return dal.AddResult(result);
        }

     }

/// <summary>
    /// 逻辑层
    /// </summary>
    /// 

    public class StudentBLL
    {
        StudentDAL dal = new StudentDAL();
        //登录
        public bool IsLogin(Student stu)
        {
            //Common com = new Common();
            //string temp = com.GetMD5String(stu.LoginPwd);
            //stu.LoginPwd = temp;
            return dal.IsLogin(stu);
        }
        ////显示学生信息
        public List<Student> StudentInfo(int gradeid)
        {
            return dal.StudentInfo(gradeid);
        }

        public List<Student> StudentInfo(string name)
        {
            return dal.StudentInfo(name);
        }
        //增加学生信息
        public int StudentAdd(Student stu)
        {
            //Common com = new Common();
            //string temp = com.GetMD5String(stu.LoginPwd);
            //stu.LoginPwd = temp;
            return dal.StudentAdd(stu);
        }
        public bool UpdateInfo(Student stu)
        {
            return dal.UpdateInfo(stu);
        }

        public DataTable SelectStudent(string gradename,string grader )
        {
            return dal.SelectStudent(gradename, grader);
        }

        public DataTable SelectStudent(string gradename)
        {
            return dal.SelectStudent(gradename);
        }

        public DataTable Student()
        {
            return dal.Student();
        }
    }

public class SubjectBLL
    {
        //加载科目信息
        SubjectDAL sdl = new SubjectDAL();
        public DataTable SubjectInfo()
        {
            return sdl.SubjectInfo();
        }

        public List<Subject> SubjectALL(int gradeid)
        {
            return sdl.SubjectALL(gradeid);
        }
    }

表示层DAL：

登录窗体：

 public partial class FrmIsLogin : Form
    {
        public FrmIsLogin()
        {
            InitializeComponent();
        }
        StudentBLL bll = new StudentBLL();
        private void btn01_Click(object sender, EventArgs e)
        {
            Student stu = new Student();
            stu.StudentNo = Convert.ToInt32(txt01.Text);
            stu.LoginPwd = txt02.Text;
            bool flag= bll.IsLogin(stu);
            if(flag)
            {
                FrmMain mm = new FrmMain();
                Hide();
                mm.Show();
                // MessageBox.Show("Test");
            }
        }
    }

主窗体：

  public partial class FrmMain : Form
    {
        public FrmMain()
        {
            InitializeComponent();
        }

        private void toolStripMenuItem1_Click(object sender, EventArgs e)
        {
            FrmAdd aa = new FrmAdd();
            aa.MdiParent = this;
            aa.Show();
        }

        private void toolStripMenuItem2_Click(object sender, EventArgs e)
        {
            FrmInfo info = new FrmInfo();
            info.MdiParent = this;
            info.Show();
        }

        private void 添加学生成绩ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            FrmResult result = new FrmResult();
            result.MdiParent = this;
            result.Show();
        }

        private void 查询学生成绩ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            FrmSelectResult sr = new FrmSelectResult();
            sr.MdiParent = this;
            sr.Show();
        }

        private void 退出ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }
    }

添加和修改学生信息窗体：

    public partial class FrmAdd : Form
    {
        public FrmAdd()
        {
            InitializeComponent();
        }
        public int no;
        public string pwd;
        public string name;
        public string phone;
        public string address;
        public string gender;
        public string gradename;
        public string email;
        public string birthday;
        public string identitycard;

        StudentBLL bll = new StudentBLL();
        //添加学生
        private void btn01_Click(object sender, EventArgs e)
        {
            //创建一个学生对象
            Student stu = new Student();
            stu.LoginPwd = txt02.Text;
            stu.StudentName = txt04.Text;
            stu.Gender = rb02.Checked ? "" : "";
            stu.Phone = txt05.Text;
            stu.Address = txt06.Text;
            stu.Birthday = Convert.ToDateTime(txt09.Text);
            stu.Email = txt07.Text;
            stu.GradeId = Convert.ToInt32(cbo01.SelectedValue);
            stu.IdentityId = txt08.Text;
            //把对象添加到数据表中

            if(txt01.Text!="")
            {

                stu.StudentNo = Convert.ToInt32(txt01.Text);
                bool flag = bll.UpdateInfo(stu);
                if (flag)
                {
                    MessageBox.Show("修改成功!");
                    foreach (Control item in gb01.Controls)
                    {
                        if (item is TextBox)
                        {
                            item.Text = "";
                        }

                    }
                    foreach (Control item in gb02.Controls)
                    {
                        if (item is TextBox)
                        {
                            item.Text = "";
                        }
                        rb01.Checked = true;
                        cbo01.Text = "";
                    }
                }

            }
            else
            {
                int result = bll.StudentAdd(stu);
                if (result>)
                {
                    txt01.Text = result.ToString();
                    MessageBox.Show("添加成功!");
                    foreach (Control item in gb01.Controls)
                    {
                        if (item is TextBox)
                        {
                            item.Text = "";
                        }

                    }
                    foreach (Control item in gb02.Controls)
                    {
                        if (item is TextBox)
                        {
                            item.Text = "";
                        }
                        rb01.Checked = true;
                        cbo01.Text = "";
                    }
                }
            }
        }

        GradeBLL gbl = new GradeBLL();
        //加载班级信息
        private void FrmAdd_Load(object sender, EventArgs e)
        {
           cbo01.ValueMember = "GradeId";
           cbo01.DisplayMember = "gradeName";
           cbo01.DataSource= gbl.GradeInfo();
            if (this.Text == "添加学生信息")
            {
                btn01.Text = "添加";
            }
            else
            {
                btn01.Text = "修改";
                txt01.Text = no.ToString();
                txt02.Text = pwd;
                txt03.Text = pwd;
                txt04.Text = name;
                if (gender.Equals())
                {
                    rb01.Checked = true;
                }
                else
                {
                    rb02.Checked = true;
                }
                txt05.Text = phone;
                txt06.Text = address;
                txt09.Text = birthday.ToString();
                txt07.Text = email;
                cbo01.Text = gradename;
                txt08.Text = identitycard;
            }

        }
    }

树状显示学生信息：

 public partial class FrmInfo : Form
    {
        public FrmInfo()
        {
            InitializeComponent();
        }
        StudentBLL sbl = new StudentBLL();
        GradeBLL bll = new GradeBLL();
        private void FrmInfo_Load(object sender, EventArgs e)
        {
            TreeNode tn= new TreeNode("全部");
            DataTable table=bll.GradeInfo();
            foreach (DataRow item in table.Rows)
            {
                TreeNode node = new TreeNode();
                node.Text = item["gradename"].ToString();
                TreeNode child = new TreeNode();
                child.Text = "男";
                child.Tag = "";
                TreeNode childs = new TreeNode();
                childs.Text = "女";
                childs.Tag = "";
                node.Nodes.Add(child);
                node.Nodes.Add(childs);
                //node.Nodes.Add("男");
                //node.Nodes.Add("女");
                tn.Nodes.Add(node);
            }
            tvList.Nodes.Add(tn);

        }

        private void tvList_AfterSelect(object sender, TreeViewEventArgs e)
        {
            if(tvList.SelectedNode.Level==)
            {
                dgvList.DataSource = sbl.Student();
            }
            else if(tvList.SelectedNode.Level==)
            {
                dgvList.DataSource=sbl.SelectStudent(tvList.SelectedNode.Text);
            }else if(tvList.SelectedNode.Level == )
            {
                if(tvList.SelectedNode.Text=="男")
                {
                    dgvList.DataSource = sbl.SelectStudent(tvList.SelectedNode.Parent.Text, Convert.ToString(tvList.SelectedNode.Tag));
                }
                else
                {
                    dgvList.DataSource = sbl.SelectStudent(tvList.SelectedNode.Parent.Text, Convert.ToString(tvList.SelectedNode.Tag));
                }

            }

        }

        private void 修改ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            FrmAdd add = new FrmAdd();
            add.Text = "修改学生成绩";
            add.no = Convert.ToInt32(dgvList.SelectedRows[].Cells[].Value);
            add.pwd = dgvList.SelectedRows[].Cells[].Value.ToString();
            add.name = dgvList.SelectedRows[].Cells[].Value.ToString();
            add.gender = dgvList.SelectedRows[].Cells[].Value.ToString();
            add.gradename = dgvList.SelectedRows[].Cells[].Value.ToString();
            add.phone = dgvList.SelectedRows[].Cells[].Value.ToString();
            add.address = dgvList.SelectedRows[].Cells[].Value.ToString();
            add.birthday= (dgvList.SelectedRows[].Cells[].Value.ToString());
            add.email = dgvList.SelectedRows[].Cells[].Value.ToString();
            add.identitycard = dgvList.SelectedRows[].Cells[].Value.ToString();
            add.Show();
        }

        private void 取消ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            FrmResult fr = new FrmResult();
            fr.no = Convert.ToInt32(dgvList.SelectedRows[].Cells[].Value);
            fr.name = dgvList.SelectedRows[].Cells[].Value.ToString();
            fr.Show();
        }
    }

添加学生成绩窗体：

  public partial class FrmResult : Form
    {
        public FrmResult()
        {
            InitializeComponent();
        }
        GradeBLL bll = new GradeBLL();
        SubjectBLL sbl = new SubjectBLL();
        ResultBLL rbl = new ResultBLL();
        private void FrmResult_Load(object sender, EventArgs e)
        {
            cbosubject.ValueMember = "subjectid";
            cbosubject.DisplayMember = "subjectname";
            cbosubject.DataSource = sbl.SubjectInfo();
            txtname.Text = name;
        }
        public int no;
        public string name;
        private void btnAdd_Click(object sender, EventArgs e)
        {
            Result rt = new Result();
            rt.StudentNo = no;
            rt.SubjectId=Convert.ToInt32(cbosubject.SelectedValue);
            rt.StudentResult = Convert.ToInt32(txtresult.Text);
            rt.ExamDate = txttime.Text;
            bool flag=rbl.AddResult(rt);
            if(flag)
            {
                MessageBox.Show("添加成功！");
            }
        }
    }

ComboBox联动:

 public partial class FrmScore : Form
    {
        public FrmScore()
        {
            InitializeComponent();
        }
        SubjectBLL bll = new SubjectBLL();
        GradeBLL gbl = new GradeBLL();
        private void cbograde_SelectedIndexChanged(object sender, EventArgs e)
        {
            int gradeid = Convert.ToInt32(cbograde.SelectedValue);
            cbosubject.ValueMember = "subjectid";
            cbosubject.DisplayMember = "subjectname";
            cbosubject.DataSource = bll.SubjectALL(gradeid);
        }

        private void FrmScore_Load(object sender, EventArgs e)
        {
            cbograde.ValueMember = "gradeid";
            cbograde.DisplayMember = "gradename";
           cbograde.DataSource= gbl.GradeInfo();
        }
    }

根据科目和年级查询和修改学生成绩窗体：

 public partial class FrmSelectResult : Form
    {
        public FrmSelectResult()
        {
            InitializeComponent();
        }
        GradeBLL bll = new GradeBLL();
        SubjectBLL sbl = new SubjectBLL();
        ResultBLL rbl = new ResultBLL();
        private void FrmSelectResult_Load(object sender, EventArgs e)
        {
            cbo01.ValueMember = "gradeid";
            cbo01.DisplayMember = "gradename";
            cbo01.DataSource = bll.GradeInfo();

            cbo02.ValueMember = "subjectid";
            cbo02.DisplayMember = "subjectname";
            cbo02.DataSource = sbl.SubjectInfo();

            cbo03.ValueMember = "subjectid";
            cbo03.DisplayMember = "subjectname";
            cbo03.DataSource = sbl.SubjectInfo();

            DataTable table = rbl.SelectResult();
            dgvList.DataSource = table;
        }
        DataTable table;
        private void button1_Click(object sender, EventArgs e)
        {
           if(txt01.Text=="")
            {
                table = rbl.SelectResult(Convert.ToInt32(cbo02.SelectedValue));
            }
           else
            {
                table = rbl.SelectResult(txt01.Text);
            }

           dgvList.DataSource = table;
        }

        private void dgvList_DoubleClick(object sender, EventArgs e)
        {
            lbl01.Text = dgvList.SelectedRows[].Cells[].Value.ToString();
            cbo03.Text = dgvList.SelectedRows[].Cells[].Value.ToString();
            txt02.Text = dgvList.SelectedRows[].Cells[].Value.ToString();
            txt03.Text = dgvList.SelectedRows[].Cells[].Value.ToString();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            Result result = new Result();
            result.StudentNo = Convert.ToInt32(dgvList.SelectedRows[].Cells[].Value);
            result.StudentResult = Convert.ToInt32(txt02.Text);
            result.SubjectId = Convert.ToInt32(cbo03.SelectedValue);
            result.ExamDate = txt03.Text;
            bool flag= rbl.UpdateResult(result);
            if(flag)
            {
                MessageBox.Show("修改成功");
                DataTable table = rbl.SelectResult();
                dgvList.DataSource = table;
            }
        }

        private void cbo01_SelectedIndexChanged(object sender, EventArgs e)
        {
            int gradeid = Convert.ToInt32(cbo01.SelectedValue);
            cbo02.ValueMember = "subjectid";
            cbo02.DisplayMember = "subjectname";
            cbo02.DataSource = sbl.SubjectALL(gradeid);
        }
    }

这个需要你自己多练习，现在学习是在学习思想，记得没事多练习.......