首先是画的图，感觉把图画完了，工程就完成了一大半，前提是画的思路是对的。还是在理解三层。
下面是画的关于数据的增删改查这个小例子的包图、类图和时序图。
包图。
类图。
时序图。
用户注册。
用户删除。
用户查询，一个是查选全部用户，一个是查询一个用户对象。
用户修改。也就是查询、删除和增加。
用户注册的代码，如下所示：
实体层代码。
Public Class UserInfo
Private userID As Integer
Private userName As String
Private userActor As String
Private userPwd As String
Private userRegDate As DateTime
Private userFlag As Boolean
'用户编号属性
Public Property UserID() As Integer
Get
Return userID
End Get
Set(ByVal value As Integer)
userID = value
End Set
End Property
'用户姓名属性
Public Property UserName() As String
Get
Return userName
End Get
Set(ByVal value As String)
userName = value
End Set
End Property
'用户角色
Public Property UserActor() As String
Get
Return userActor
End Get
Set(ByVal value As String)
userActor = value
End Set
End Property
'用户密码
Public Property UserPwd() As String
Get
Return userPwd
End Get
Set(ByVal value As String)
userPwd = value
End Set
End Property
'用户注册日期
Public Property UserRegDate() As DateTime
Get
Return userRegDate
End Get
Set(ByVal value As DateTime)
userRegDate = value
End Set
End Property
'用户合法标致
Public Property UserFlag
Get
Return userFlag
End Get
Set(ByVal value)
userFlag = value
End Set
End Property
End Class
DAL层代码。
Imports System.Data.SqlClient
'DAL包中的DALuser类。
Public Class DALUser
'数据库连接字符串
Dim connStr As String = "Data Source=192.168.24.63;Initial Catalog=PCharge_Sys;User ID=sa;Password=sa"
''' <summary>
''' 添加一条用户信息
''' </summary>
''' <param name="EntityUserInfo">一个用户对象</param>
''' <returns>是否添加成功</returns>
''' <remarks>2012年1月19号 20：31</remarks>
Public Function DALUserAdd(ByVal EntityUserInfo As Entity.UserInfo) As Boolean
Dim sql As String = "Insert into UserInfo(UserID,UserName,UserActor,UserPwd,UserRegDate,UserFlag)" _
& " values (@UserID,@UserName,@UserActor,@UserPwd,@UserRegDate,@UserFlag) "
Dim conn As SqlConnection = New SqlConnection(connStr)
Dim cmd As SqlCommand = New SqlCommand(sql, conn)
Dim sqlParam As New SqlParameter
sqlParam = New SqlParameter("@UserID", SqlDbType.Int)
sqlParam.Value = EntityUserInfo.UserID
cmd.Parameters.Add(sqlParam)
sqlParam = New SqlParameter("@UserName", SqlDbType.VarChar)
sqlParam.Value = EntityUserInfo.UserName
cmd.Parameters.Add(sqlParam)
sqlParam = New SqlParameter("@UserActor", SqlDbType.VarChar)
sqlParam.Value = EntityUserInfo.UserActor
cmd.Parameters.Add(sqlParam)
sqlParam = New SqlParameter("@UserPwd", SqlDbType.VarChar)
sqlParam.Value = EntityUserInfo.UserPwd
cmd.Parameters.Add(sqlParam)
sqlParam = New SqlParameter("@UserRegDate", SqlDbType.DateTime)
sqlParam.Value = EntityUserInfo.UserRegDate
cmd.Parameters.Add(sqlParam)
sqlParam = New SqlParameter("@UserFlag", SqlDbType.Bit)
sqlParam.Value = EntityUserInfo.UserFlag
cmd.Parameters.Add(sqlParam)
Try
conn.Open()
Return cmd.ExecuteNonQuery() > 0
Catch ex As Exception
Return False
End Try
If Not IsNothing(conn) Then
conn.Close()
conn = Nothing
End If
End Function
End Class
BLL层代码。
Imports DAL
''' <summary>
''' BLL包中的BLLUser类。
''' </summary>
''' <remarks></remarks>
Public Class BLLUser
''' <summary>
''' 插入一条用户信息
''' </summary>
''' <param name="EntityUserInfo"></param>
''' <returns></returns>
''' <remarks></remarks>
Public Function BLLUserAdd(ByVal EntityUserInfo As Entity.UserInfo) As Boolean
Dim DALUserInfo As New DAL.DALUser
Return DALUserInfo.DALUserAdd(EntityUserInfo)
End Function
End Class
UI层代码。
界面层。
'界面层。
Public Class UserAddForm
''' <summary>
''' 用户注册，并对用户的输入加以判断。
''' </summary>
''' <param name="sender"></param>
''' <param name="e"></param>
''' <remarks></remarks>
Private Sub RegisterBut_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RegisterBut.Click
If txtUserID.Text = "" Or txtUserName.Text = "" Or txtUserPwd.Text = "" Or txtUserRegDate.Text = "" Or txtUserActor.Text = "" Or txtUserFlag.Text = "" Then
MsgBox("输入不能为空！请重新输入！")
Else
If Not IsNumeric(txtUserID.Text) Then
MsgBox("输入的编号因为数字！请重新输入！")
End If
If Not IsDate(txtUserRegDate.Text) Then
MsgBox("输入的注册日期请为日期XXXX-XX-XX格式!")
Else
Dim EntityUserInfo As New Entity.UserInfo
EntityUserInfo.UserID = txtUserID.Text
EntityUserInfo.UserName = txtUserName.Text
EntityUserInfo.UserActor = txtUserActor.Text
EntityUserInfo.UserPwd = txtUserPwd.Text
EntityUserInfo.UserRegDate = txtUserRegDate.Text
EntityUserInfo.UserFlag = txtUserFlag.Text
Dim BLLUserInfo As New BLL.BLLUser
If BLLUserInfo.BLLUserAdd(EntityUserInfo) Then
MsgBox("添加成功！")
Else
MsgBox("添加失败！")
End If
End If
End If
End Sub
End Class
上面是在数据库表中插入一条记录，其他的删除和修改，查询类似，就是DAL和BLL层返回值可能不同。
DAL层删除查询代码，保存备后用。
''' <summary>
''' 获得所有用户
''' </summary>
''' <returns>所有用户的DataSet集合</returns>
''' <remarks></remarks>
Public Function DALUserSelectAll() As DataSet
Dim sql As String = "select * from UserInfo"
Dim conn As SqlConnection = New SqlConnection(connStr)
Dim cmd As SqlCommand = New SqlCommand(sql, conn)
Dim dap As SqlDataAdapter = New SqlDataAdapter(cmd)
Dim ds As New DataSet
Try
conn.Open()
dap.Fill(ds)
Return ds
Catch ex As Exception
Return Nothing
Finally
If Not IsNothing(cmd) Then
cmd.Dispose()
cmd = Nothing
End If
If Not IsNothing(conn) Then
conn.Close()
conn = Nothing
End If
End Try
End Function
''' <summary>
''' 获得一个用户的信息。
''' </summary>
''' <param name="UserID"></param>
''' <returns>一个用户的对象</returns>
''' <remarks></remarks>
Public Function DALUserGetObject(ByVal UserID As Integer) As Entity.UserInfo
Dim sql As String = "select UserName,UserActor,UserPwd,UserRegDate,UserFlag from UserInfo where UserID=@UserID"
Dim conn As SqlConnection = New SqlConnection(connStr)
Dim cmd As SqlCommand = New SqlCommand(sql, conn)
Dim sqlParam As New SqlParameter("@UserID", SqlDbType.Int)
sqlParam.Value = UserID
Dim sdr As SqlDataReader = Nothing
Dim DALEntityUserinfo As New Entity.UserInfo
Try
sdr = cmd.ExecuteReader()
While sdr.Read
DALEntityUserinfo.UserID = UserID
DALEntityUserinfo.UserName = sdr.GetString(0)
DALEntityUserinfo.UserActor = sdr.GetString(1)
DALEntityUserinfo.UserPwd = sdr.GetString(2)
DALEntityUserinfo.UserRegDate = sdr.GetString(3)
DALEntityUserinfo.UserFlag = sdr.GetString(4)
End While
Return DALEntityUserinfo
Catch ex As Exception
Return Nothing
Finally
If Not IsNothing(sdr) Then
sdr.Close()
sdr = Nothing
End If
If Not IsNothing(cmd) Then
cmd.Dispose()
cmd = Nothing
End If
If Not IsNothing(conn) Then
conn.Close()
conn = Nothing
End If
End Try
End Function
Public Function DALUserDel(ByVal DALEntityUserinfo As Entity.UserInfo) As Boolean
Dim sql As String = "delete from UserInfo where UserID=@UserID"
Dim conn As SqlConnection = New SqlConnection(connStr)
Dim cmd As SqlCommand = New SqlCommand(sql, conn)
Dim sqlParam As New SqlParameter("@UserID", SqlDbType.Int)
sqlParam.Value = DALEntityUserinfo.UserID
Try
conn.Open()
Return cmd.ExecuteNonQuery() > 0
Catch ex As Exception
Return False
Finally
If Not IsNothing(cmd) Then
cmd.Dispose()
cmd = Nothing
End If
If Not IsNothing(conn) Then
conn.Close()
conn = Nothing
End If
End Try
End Function
End Class
以上只是为了理解而理解，所以做小例子，可能有很多缺陷，欢迎您指教。