GDB Debug Core Dump file Example

The last chapter discusses the basic concept, function and relationship of three layer, and now shows the simple application of three-layer structure design idea in the process of user landing in the system.

Vb. NET operation is as follows

Start by building the following Windows applications and class libraries

First, create the entity class

Public Class userInfo    Private _username As String Public property    username As String        Get            Return _ Username        End Get        Set (ByVal value as String)            _username = value        End Set    End Property    Private _pwd As String public property    Pwd As String        Get            Return _pwd        End Get        Set (value as String)            _pwd = value        End Set    end Propertyend Class

UI layer, provided that the reference entity class (model) and the BLL

Public Class Form1    Private Sub btncancel_click (sender as Object, e as EventArgs) Handles Btncancel.click        me.close  ()    End Sub    Private Sub btnok_click (sender as Object, e as EventArgs) Handles btnok.click        Try            Dim Euser2 as New Model.userinfo            Dim Euser3 as New model.userinfo            euser2. UserName = TxtUserName.Text.Trim ' passes the U-layer data to the entity            Euser2. PWD = TxtPassword.Text.Trim            Dim Mgr as New BLL. Loginmannager ' passes the data to layer b            euser3 = Mgr. Userlogin (euser2)        Catch ex as Exception            MessageBox.Show (ex. Message.tostring ())        End Try    End subend Class

DAL layer: Precondition Referencing entity class

Imports system.dataimports System.Data.SqlClientImports modelpublic Class user ' CREATE DATABASE link public conn as New Sqlconnec tion ("Server=lxy;database=login;user id=sa;password=123456") Public Function Selectuser (ByVal user as Model.userinfo) As Model.userinfo ' passes the entity uesrinfo instead of the parameter id.username, which makes it easy to call the parameters in the entity Dim reader As SqlDataReader Dim euse R as New model.userinfo Dim sql as String = "Select Username,password from User_info WHERE [email protected] A nd [email protected] "Dim cmd as New SqlCommand (SQL, conn) cmd. CommandText = sql cmd. CommandType = CommandType.Text cmd. Parameters.Add (New SqlParameter ("@username", User.username)) cmd. Parameters.Add (New SqlParameter ("@password", USER.PWD)) Conn. Open () reader = cmd. ExecuteReader while reader. Read () Euser.username = reader. GetString (0) euser.pwd = reader. GetString (1) End while Return Euser Conn. Close () End functionend Class 

Next is the BLL layer: a precondition to reference the Dal and the entity class

Public Class Loginmannager Public    Function userlogin (ByVal User as Model.userinfo) as Model.userinfo        Dim Udao as N EW Dal.user        Dim eUser1 as New model.userinfo        eUser1 = udao.selectuser (user) transmits data to D-tier        If IsNothing ( Euser1.username) then            Throw New Exception ("Login failed, please verify login name and password!") ")        Else            MsgBox (" landed successfully! ")            Return eUser1        end If    End FunctionEnd Class

References:we see the main features of the three-tier architecture: The UI calls the method of the BLL class, that is, the UI knows the method of the BLL, but does not know the details of the method implementation, and the BLL layer does not know the existence of the UI. The same BLL layer calls the DAL, and the DAL does not know the existence of the BLL. Any change in any of the three accesses than either will not affect the normal work of the other two, only to readjust the change. Layer three passes an instance of an entity class as a parameter.
in short, the presentation layer only provides interfaces for software systems to interact with the user, and the business logic layer is the bridge between the interface layer and the data access layer, which is responsible for data processing and transmission;