三层架构学生管理系统简单代码

以下是一个简单的三层架构学生管理系统的代码示例：

**数据访问层（Data Access Layer，DAL）：**

public class StudentDAL
{
    private SqlConnection connection;

    public StudentDAL(string connectionString)
    {
        connection = new SqlConnection(connectionString);
    }

    public List<Student> GetStudents()
    {
        List<Student> students = new List<Student>();

        SqlCommand command = new SqlCommand("SELECT * FROM Students", connection);
        connection.Open();
        SqlDataReader reader = command.ExecuteReader();
        while (reader.Read())
        {
            Student student = new Student();
            student.ID = Convert.ToInt32(reader["ID"]);
            student.Name = reader["Name"].ToString();
            student.Age = Convert.ToInt32(reader["Age"]);
            students.Add(student);
        }
        reader.Close();
        connection.Close();

        return students;
    }

    public void AddStudent(Student student)
    {
        SqlCommand command = new SqlCommand("INSERT INTO Students (Name, Age) VALUES (@Name, @Age)", connection);
        command.Parameters.AddWithValue("@Name", student.Name);
        command.Parameters.AddWithValue("@Age", student.Age);
        connection.Open();
        command.ExecuteNonQuery();
        connection.Close();
    }
}

**业务逻辑层（Business Logic Layer，BLL）：**

public class StudentBLL
{
    private StudentDAL studentDAL;

    public StudentBLL(string connectionString)
    {
        studentDAL = new StudentDAL(connectionString);
    }

    public List<Student> GetStudents()
    {
        return studentDAL.GetStudents();
    }

    public void AddStudent(Student student)
    {
        studentDAL.AddStudent(student);
    }
}

**用户界面层（User Interface Layer，UI）：**

public partial class MainForm : Form
{
    private StudentBLL studentBLL;

    public MainForm()
    {
        InitializeComponent();
        studentBLL = new StudentBLL("connectionString");
    }

    private void MainForm_Load(object sender, EventArgs e)
    {
        RefreshStudentList();
    }

    private void btnAdd_Click(object sender, EventArgs e)
    {
        Student student = new Student();
        student.Name = txtName.Text;
        student.Age = Convert.ToInt32(txtAge.Text);
        studentBLL.AddStudent(student);
        RefreshStudentList();
    }

    private void RefreshStudentList()
    {
        List<Student> students = studentBLL.GetStudents();
        lvStudents.Items.Clear();
        foreach (Student student in students)
        {
            ListViewItem item = new ListViewItem(student.ID.ToString());
            item.SubItems.Add(student.Name);
            item.SubItems.Add(student.Age.ToString());
            lvStudents.Items.Add(item);
        }
    }
}

以上代码示例中，数据访问层负责与数据库交互，业务逻辑层负责处理业务逻辑，用户界面层负责与用户进行交互。三层架构可以有效地分离关注点，使得代码更加清晰、易于维护。