机房收费系统中，一个比较让人纠结功能就是组合查询，不仅仅是代码比较多，而且大多都是重复的代码，也正是因为如此，才比较适合模版方法模式。

一、基本介绍

模版方式模式是定义一个操作中的算法的骨架，而将步骤延迟到子类中。

模板方法使得子类可以不改变一个算法的结构即可重定义算法的某些特定步骤。

类图

二、具体实现

1、建立模板父窗体

添加Windows窗体，设计模板界面（如下图），并在模板窗体里写入抽象出来的类和方法的代码。

'*************************************************   
'作者：崔晓光  
'小组：    
'说明：组合查询模板  
'创建日期：2014.9.9  
'版本号：  
'**********************************************/ 
Imports Entity
Imports Microsoft.Office.Interop.Excel
Imports Microsoft.Office.Interop
Imports System.Data
Imports System.IO
'组合查询父窗体
Public Class FrmComQueryParent
    '实例化一个组合查询的实体
    Protected comQueryEntity As New ComQueryEntity
    ’加载
    Protected Sub FrmComQueryParent_Load(sender As Object,e As EventArgs) Handles MyBase.Load
 
        '将参数传递给实体，赋初值
 
        '字段名
        comQueryEntity.CmbName1 = ""
        comQueryEntity.CmbName2 = ""
        comQueryEntity.CmbName3 = ""
 
        '操作符
        cmbMark1.Items.Add(">")
        cmbMark1.Items.Add("<")
        cmbMark1.Items.Add("=")
        cmbMark1.Items.Add("<>")
 
        cmbMark2.Items.Add(">")
        cmbMark2.Items.Add("<")
        cmbMark2.Items.Add("=")
        cmbMark2.Items.Add("<>")
 
        cmbMark3.Items.Add(">")
        cmbMark3.Items.Add("<")
        cmbMark3.Items.Add("=")
        cmbMark3.Items.Add("<>")
 
        '关系
        cmbRelation1.Items.Add("与")
        cmbRelation1.Items.Add("或")
 
        cmbRelation2.Items.Add("与")
        cmbRelation2.Items.Add("或")
 
        '窗体加载后，后两组查询默认不能用
        cmbName2.Enabled = False
        cmbName3.Enabled = False
        cmbMark2.Enabled = False
        cmbMark3.Enabled = False
 
        cmbRelation2.Enabled = False
        txtContent2.Enabled = False
        txtContent3.Enabled = False
 
        Dim i As Integer
        For i = 0 To dgvRecord.Columns.Count - 1
            dgvRecord.Columns(i).Width = DataGridViewAutoSizeColumnMode.AllCells   '调整列宽为根据内容自动调整
        Next
    End Sub
    '查询
    Private Sub btQuery_Click(sender As Object,e As EventArgs) Handles btQuery.Click
 
        Try
            '判断组合框不为空
            If cmbRelation1.Text = "" Then
                If cmbName1.Text = "" Or cmbMark1.Text = "" Or txtContent1.Text = "" Then
                    MsgBox("第一行查询条件不能为空，请完善查询信息！",CType(vbOKOnly + MsgBoxStyle.Exclamation,MsgBoxStyle),"提示")
                    Exit Sub
                End If
            End If
 
            If cmbRelation1.Text <> "" Then
                If cmbName1.Text = "" Or cmbMark1.Text = "" Or txtContent1.Text = "" Or cmbName2.Text = "" Or cmbMark2.Text = "" Or txtContent2.Text = "" Then
                    MsgBox("所输入的查询条件不能为空，请完善查询信息！","提示")
                    Exit Sub
                End If
            End If
 
            If cmbRelation2.Text <> "" Then
                If cmbName1.Text = "" Or cmbMark1.Text = "" Or txtContent1.Text = "" Or cmbName2.Text = "" Or cmbMark2.Text = "" Or txtContent2.Text = "" Or cmbName3.Text = "" Or cmbMark3.Text = "" Or txtContent3.Text = "" Then
                    MsgBox("所输入的查询条件不能为空，请完善查询信息！","提示")
                    Exit Sub
                End If
            End If
 
            '将参数传给实体
            comQueryEntity.DbName = GetdbName()
            comQueryEntity.CmbName1 = ToEnglish(cmbName1.Text)
            comQueryEntity.CmbName2 = ToEnglish(cmbName2.Text)
            comQueryEntity.CmbName3 = ToEnglish(cmbName3.Text)
 
            comQueryEntity.CmbMark1 = cmbMark1.Text.Trim
            comQueryEntity.CmbMark2 = cmbMark2.Text.Trim
            comQueryEntity.CmbMark3 = cmbMark3.Text.Trim
 
            '在查询时非数字要加上''
            If IsNumeric(txtContent1.Text) Then
                comQueryEntity.TxtContent1 = txtContent1.Text.Trim
            Else
                comQueryEntity.TxtContent1 = "'" & txtContent1.Text.Trim & "'"
            End If
            If IsNumeric(txtContent2.Text) Then
                comQueryEntity.TxtContent2 = txtContent2.Text.Trim
            Else
                comQueryEntity.TxtContent2 = "'" & txtContent2.Text.Trim & "'"
            End If
            If IsNumeric(txtContent3.Text) Then
                comQueryEntity.TxtContent3 = txtContent3.Text.Trim
            Else
                comQueryEntity.TxtContent3 = "'" & txtContent3.Text.Trim & "'"
            End If
 
            '前者还是后者  
            comQueryEntity.CmbRelation1 = ToEnglish(cmbRelation1.Text)
            comQueryEntity.CmbRelation2 = ToEnglish(cmbRelation2.Text)
 
 
            Dim dt As New Data.DataTable
            Dim facadeGeneral As New Facade.Facade.FacadeGeneral
 
            ' 把表显示到datagridview中  
            Call Todgv(comQueryEntity)
 
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub
 
    ''' <summary>  
    ''' 模板方法，定义虚函数ToEnglish，查询字段转化为数据库字段  
    ''' </summary>  
    ''' <param name="cmbName"></param>  
    ''' <returns></returns>  
    ''' <remarks></remarks>  
    Public Overridable Function ToEnglish(cmbName As String) As String
        Return ""
 
    End Function
    ''' <summary>  
    ''' 获得数据库表名  
    ''' </summary>  
    ''' <returns></returns>  
    ''' <remarks></remarks>  
    Protected Overridable Function GetdbName() As String
        Return ""
    End Function
 
    ''' <summary>  
    ''' 把表显示到datagridview中  
    ''' </summary>  
    ''' <remarks></remarks>  
    Protected Overridable Sub Todgv(ByVal comQueryEntity As ComQueryEntity)
 
    End Sub
 
    ''' <summary>  
    ''' 拼接字符串  
    ''' </summary>  
    ''' <param name="frm"></param>  
    ''' <returns></returns>  
    ''' <remarks></remarks> 
    Public Function Query(frm As FrmComQueryParent,ByVal comQueryEntity As ComQueryEntity) As String
 
        Dim cmdText As String = "" & frm.ToEnglish(frm.cmbName1.Text) & frm.cmbMark1.Text & "" & comQueryEntity.TxtContent1 & ""
 
        '非组合查询
        If frm.cmbRelation1.Text = "" Then
            cmdText = cmdText
            '关系2为空，关系1不为空
        ElseIf frm.cmbRelation2.Text = "" Then
            cmdText = cmdText & frm.ToEnglish(frm.cmbRelation1.Text) & "" & frm.ToEnglish(frm.cmbName2.Text) & frm.cmbMark2.Text & "" & comQueryEntity.TxtContent2 & ""
        Else
            '关系1，2都不为空
            cmdText = cmdText & frm.ToEnglish(frm.cmbRelation1.Text) & "" & _
                        frm.ToEnglish(frm.cmbName2.Text) & frm.cmbMark2.Text & "'" & comQueryEntity.TxtContent2 & "'" & "" & _
                        frm.ToEnglish(frm.cmbRelation2.Text) & "" & _
                        frm.ToEnglish(frm.cmbName3.Text) & frm.cmbMark3.Text & "'" & comQueryEntity.TxtContent3 & "'"
        End If
 
        Return cmdText
 
    End Function
 
 
    ''' <summary>  
    ''' 第一个组合关系是否为空  
    ''' </summary>  
    ''' <param name="sender"></param>  
    ''' <param name="e"></param>  
    ''' <remarks></remarks>  
 
    Private Sub cmbRelation1_SelectedIndexChanged(sender As Object,e As EventArgs) Handles cmbRelation1.SelectedIndexChanged
 
        If cmbRelation1.Text = "" Then
            cmbName2.Enabled = False
            cmbName3.Enabled = False
            cmbMark2.Enabled = False
            cmbMark3.Enabled = False
 
            cmbRelation2.Enabled = False
            txtContent2.Enabled = False
            txtContent3.Enabled = False
        Else
            cmbName2.Enabled = True
            cmbMark2.Enabled = True
            cmbRelation2.Enabled = True
            txtContent2.Enabled = True
        End If
    End Sub
 
    ''' <summary>  
    ''' 第二个组合关系是否为空  
    ''' </summary>  
    ''' <param name="sender"></param>  
    ''' <param name="e"></param>  
    ''' <remarks></remarks>  
    Private Sub cmbRelation2_SelectedIndexChanged(sender As Object,e As EventArgs) Handles cmbRelation2.SelectedIndexChanged
 
        If cmbRelation2.Text = "" Then
            cmbName3.Enabled = False
            cmbMark3.Enabled = False
            txtContent3.Enabled = False
        Else
            cmbName3.Enabled = True
            cmbMark3.Enabled = True
            txtContent3.Enabled = True
        End If
 
    End Sub
    ''' <summary>
    ''' 关闭该窗体
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Private Sub btCancel_Click(sender As Object,e As EventArgs) Handles btCancel.Click
        Me.Close()
    End Sub
 
 
    '导出为Excel
    Private Sub Button1_Click(sender As Object,e As EventArgs) Handles Button1.Click
 
         '要先添加引用才能用到 Microsoft.Office.Interop.Excel.Application()
        Dim MyExcel As New Microsoft.Office.Interop.Excel.Application()
        MyExcel.Application.Workbooks.Add(True)
        MyExcel.Visible = True
 
        '去除dgvRecord的编号列（这里也可以不要）
        Dim m As Integer
        For m = 0 To dgvRecord.ColumnCount - 1
            MyExcel.Cells(1,m + 1) = Me.dgvRecord.Columns(m).HeaderText
        Next m
 
        '往excel表里添加数据
        Dim i As Integer
        For i = 0 To Me.dgvRecord.RowCount - 1
            Dim j As Integer
            For j = 0 To dgvRecord.ColumnCount - 1
                If Me.dgvRecord(j,i).Value Is System.DBNull.Value Then
 
                    MyExcel.Cells(i + 2,j + 1) = ""
                Else
                    MyExcel.Cells(i + 2,j + 1) = dgvRecord(j,i).Value.ToString
 
                End If
            Next j
        Next i
    End Sub
 
End Class

2、建立子窗体

如下图建立子窗体，选择继承创建的父窗体模板，然后就可以得到一模一样的子窗体了。通过在子窗体里重写一些方法和类，以实现不同的功能就可以了。

实现上机学生查询的代码如下：

'*************************************************   
'作者：崔晓光  
'小组：    
'说明：学生上机组合查询 
'创建日期：2014.9.9  
'版本号：  
'**********************************************/ 
 
Imports Entity.Entity
Imports Entity
 
'学生正在上机查询
Public Class FrmComQueryStudentOn
 
    ''' <summary>  
    ''' 加载combo的item  
    ''' </summary>  
    ''' <param name="sender"></param>  
    ''' <param name="e"></param>  
    ''' <remarks></remarks>  
    Private Sub FrmComQueryStudentOn_Load(sender As Object,e As EventArgs) Handles MyBase.Load
 
        cmbName1.Items.Add("卡号")
        cmbName1.Items.Add("上机日期")
        cmbName1.Items.Add("上机时间")
        cmbName1.Items.Add("机器名")
 
        cmbName2.Items.Add("卡号")
        cmbName2.Items.Add("上机日期")
        cmbName2.Items.Add("上机时间")
        cmbName2.Items.Add("机器名")
 
        cmbName3.Items.Add("卡号")
        cmbName3.Items.Add("上机日期")
        cmbName3.Items.Add("上机时间")
        cmbName3.Items.Add("机器名")
 
    End Sub
 
    ''' <summary>  
    ''' 把加载的汉字转换成数据库的字段  
    ''' </summary>  
    ''' <param name="cmbName"></param>  
    ''' <returns></returns>  
    ''' <remarks></remarks>  
    Public Overrides Function ToEnglish(cmbName As String) As String
 
        Select Case cmbName
            Case "卡号"
                ToEnglish = "cardId"
            Case "上机日期"
                ToEnglish = "onDate"
            Case "上机时间"
                ToEnglish = "onTime"
            Case "机器名"
                ToEnglish = "local"
            Case "与"
                ToEnglish = " and "
            Case "或"
                ToEnglish = " or "
            Case Else
                ToEnglish = ""
        End Select
 
    End Function
 
    ''' <summary>  
    ''' 传数据库表名  
    ''' </summary>  
    ''' <returns></returns>  
    ''' <remarks></remarks>  
    Protected Overrides Function GetdbName() As String
        Return "LineRecord_Info"
    End Function
 
    ''' <summary>  
    ''' 查询并把数据显示到datagridview中  
    ''' </summary>  
    ''' <remarks></remarks>  
    Protected Overrides Sub Todgv(ByVal comQueryEntity As ComQueryEntity)
 
        Dim returnList As New List(Of LineRecordEntity)        '实例化集合，用来返回实体类
        Dim frmComQueryParent As New FrmComQueryParent         '实例化父窗体
        Dim facadeComQuery As New Facade.FacadeComQuery        '实例化外观
 
        Try
            comQueryEntity.sqlString = frmComQueryParent.Query(Me,comQueryEntity)   '获得拼接字符串
            returnList = facadeComQuery.QueryStudentOn(comQueryEntity)           '调用外观进行查询
            '取出返回的实体
            Dim lineRecordEntity As LineRecordEntity
            Dim dataTable As New Data.DataTable
 
            dataTable.Columns.Add("卡号")          '自动创建列
            dataTable.Columns.Add("上机日期")
            dataTable.Columns.Add("上机时间")
            dataTable.Columns.Add("机器名")
            Dim datanewRow As DataRow   '声明一个新行
            For i = 0 To returnList.Count - 1
                lineRecordEntity = returnList.Item(i)
                datanewRow = dataTable.NewRow()
                '显示数据
                datanewRow.Item(0) = lineRecordEntity.CardId
                datanewRow.Item(1) = lineRecordEntity.OnDate
                datanewRow.Item(2) = lineRecordEntity.OnTime
                datanewRow.Item(3) = lineRecordEntity.Local
 
                dataTable.Rows.Add(datanewRow)           '将新行插入到表中
            Next
 
            '绑定数据源
            dgvRecord.AutoGenerateColumns = True           '自动创建列
            dgvRecord.AllowUserToAddRows = False
            Me.dgvRecord.DataSource = dataTable              '显示信息
            Me.dgvRecord.Refresh()
 
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub
End Class

3.DAL层，具体的查询

我们虽然传的是实体，但实际上是一个字符串，所以在D层，只要将字符串拼接起来就行

        ''' <summary>
        ''' 从表中查询学生上机信息,组合查询
	''' </summary>
        ''' <param name="comQueryEntity">上机记录实体</param>
        Public Function QueryOn(ByVal comQueryEntity As Entity.ComQueryEntity) As List(Of Entity.Entity.LineRecordEntity) Implements ILineRecord.QueryOn
 
            Try
                strsql = "select * from (select * from LineRecord_Info where offStatus='正在上机')as LineRecord_Info where " & comQueryEntity.sqlString.Trim
 
                dataTable = sqlHelper.ExecSelectNo(CommandType.Text,strsql)
 
                Dim returnList As New List(Of LineRecordEntity)
                Dim lineRecordEntity As New LineRecordEntity
 
                '封装查到的实体
                For i = 0 To dataTable.Rows.Count - 1
                    lineRecordEntity.CardId = dataTable.Rows(i).Item(0).ToString
                    lineRecordEntity.OnDate = dataTable.Rows(i).Item(1).ToString
                    lineRecordEntity.OnTime = dataTable.Rows(i).Item(2).ToString
                    lineRecordEntity.Local = dataTable.Rows(i).Item(8).ToString
 
                    returnList.Add(lineRecordEntity)
                Next
                Return returnList
            Catch ex As Exception
                Throw
            End Try
        End Function

三、总结

自此，模版方法模式已经做完。这里注意的是组合查询的查询语句的方式，详见

机房收费系统 之 组合查询BUG。

模版方法的核心就是将整体架构抽象到父类中，具体的时间情况由子类拓展。在我们学习生活中也是，学者去抽象，去总结，这样才能提升层次。