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首页 - 经验之谈 - VB COM基础讲座之类的测试
发表评论(0)作者:不详, 平台:VB6.0+Win98, 阅读:7911, 日期:2004-10-30
 现在就来测试前面创建的类。

  按F5运行程序;在弹出的属性对话框中,选中"Wait for Components to Start"(启动工程时等待创建部件),然后按[OK]按钮;



  这时,类就会被激活,其他程序就可使用它的功能。

  再次运行Visual Basic另一个实例;

  创建一个新的"Standard EXE"工程;

  选择"注释:Project"->"References"菜单;

  浏览对话框中可引用的列表项,可以发现一些额外的组件。

  选中"Northwind"列表项;

  Northwind就是前面创建的ActiveX工程。

  单击[OK]按钮;

  现在添加一些代码来使用上述工程:

  在Form1表单中添加一个命令按钮;为命令按钮添加下列代码:

  Dim Test As Customers
  Set Test = New Customers
  MsgBox Test.CustomerID
  Set Test = Nothing

  该代码首先创建一个新的Customers对象,然后显示CustomerID信息,最后将Test对象置为Nothing,并关闭它。

  按F5键运行测试程序;

  需要说明的是,当运行时出现"invalid reference"错误提示时,肯定哪些地方有问题。这时可按下面步骤重新来一次:

  (1) 在测试工程中去掉Northwind引用;

  (2) 重新启动Northwind工程;

  (3) 在测试工程中添加Northwind引用,再运行!

  单击表单中的命令按钮;

  这时运行时可能需要几秒钟,毕竟还要做一些如数据库连接等工作。但是,除了一开始的停留外,后面的调用就快得多了。程序将显示包含"ALFKI"的消息对话框。

  关闭测试程序。

  现在,我们来看看程序背后究竟发生什么。

  将插入符移动到MsgBox Test.CustomerID这条语句上;按F9;

  该语句显示为红色,用来标记一个断点。当代码运行时,它会停留在这里。按F8将单步运行此语句,并移动到下一句代码上。

  按F5再次运行测试程序;

  单击命令按钮;

  流程将停留在MsgBox这条命令上。

  按F8,慢慢单步执行各条语句;

  将会看到系统在两个Visual Basic中来回切换,显示出不同属性的处理过程。

  结束后,关闭测试程序。

  下面再对前面的工程进行测试。这一次,我们不仅获取CustomerID的值,而且还设置这个值。

  将命令按钮的代码改为:

  Dim Test As Customers
  Set Test = New Customers
  Test.CustomerID = "KARLY"
  Test.Update
  MsgBox Test.CustomerID
  Set Test = Nothing

  该代码首先设置"CustomerID"字段,然后更新记录集,最后显示出CustomerID属性,其结果应该是设置的"KARLY"。

  假如愿意,仍然可以按F9高亮显示"Test.CustomerID =" 这条语句,然后按F8单步运行来查看其工作情况。

  至此,我们已经成功地创建并测试一个简单的基于数据库的类。但是,还没有对customerID的字符串长度作测试,如果其长度超过5个字符,看看会发生什么?

下一步,我们将扩充并改进这个数据库类。

  首先添加类的几个特征:其他的属性、一些方法甚至一两个事件。 其相应的代码如下:

  Dim WithEvents rs As Recordset
  Public Event RecordsetMove()
  Private Sub Class_Initialize()
   Set rs = New Recordset
   rs.ActiveConnection = "Provider=Microsoft." & _"Jet.OLEDB.4.0;Data Source=C:\Program Files\" & _"Microsoft Visual Studio\VB98\Nwind.mdb;" & _"Persist Security Info=False"
   rs.Open "select * from customers", , adOpenKeyset, adLockOptimistic
  End Sub

  Private Sub Class_Terminate()
   rs.Close
   Set rs = Nothing
  End Sub

  Public Property Get CustomerID() As String
   CustomerID = rs("CustomerID")
  End Property

  Public Property Let CustomerID(NewValue As String)
   注释:If the length of NewValue is greater than five
   If Len(NewValue) > 5 Then
    注释:... then raise an error to the program
    注释:using this class, by running
    注释:Err.Raise vbObjectError + OurErrorNumber
    Err.Raise vbObjectError + 1, "CustomerID", _"Customer ID can only be up to five " & _ "characters long!"

   Else
    注释:... otherwise, change the field value
    rs("CustomerID") = NewValue
   End If
  End Property
  Public Property Get CompanyName() As Variant
   CompanyName = rs("CompanyName")
  End Property

  Public Property Let CompanyName(ByVal NewValue As Variant)
   rs("CompanyName") = NewValue
  End Property

  Public Property Get ContactName() As Variant
   ContactName = rs("ContactName")
  End Property

  Public Property Let ContactName(ByVal NewValue As Variant)
    rs("ContactName") = NewValue
  End Property

  Public Property Get ContactTitle() As Variant
   ContactTitle = rs("ContactTitle")
  End Property

  Public Property Let ContactTitle(ByVal NewValue As Variant)
   rs("ContactTitle") = NewValue
  End Property

  Public Property Get Address() As Variant
   Address = rs("Address")
  End Property

  Public Property Let Address(ByVal NewValue As Variant)
   rs("Address") = NewValue
  End Property

  Public Property Get City() As Variant
   City = rs("City")
  End Property

  Public Property Let City(ByVal NewValue As Variant)
   rs("City") = NewValue
  End Property

  Public Property Get Region() As Variant
    Region = rs("Region")
  End Property

  Public Property Let Region(ByVal NewValue As Variant)
   rs("Region") = NewValue
  End Property

  Public Property Get PostalCode() As Variant
   PostalCode = rs("PostalCode")
  End Property

  Public Property Let PostalCode(ByVal NewValue As Variant)
   rs("PostalCode") = NewValue
  End Property

  Public Property Get Country() As Variant
   Country = rs("Country")
  End Property

  Public Property Let Country(ByVal NewValue As Variant)
   rs("Country") = NewValue
  End Property

  Public Property Get Phone() As Variant
   Phone = rs("Phone")
  End Property

  Public Property Let Phone(ByVal NewValue As Variant)
   rs("Phone") = NewValue
  End Property

  Public Property Get Fax() As Variant
   Fax = rs("Fax")
  End Property

  Public Property Let Fax(ByVal NewValue As Variant)
   rs("Fax") = NewValue
  End Property

  Public Sub AddNew()
   rs.AddNew
  End Sub

  Public Sub Update()
   rs.Update
  End Sub

  Public Sub CancelUpdate()
   If rs.EditMode = adEditInProgress Or _rs.EditMode = adEditAdd Then
    rs.CancelUpdate
   End If
  End Sub
  Public Sub MoveNext()
   rs.MoveNext
  End Sub

  Public Sub MovePrevious()
   rs.MovePrevious
  End Sub

  Public Sub MoveFirst()
   rs.MoveFirst
  End Sub

  Public Sub MoveLast()
   rs.MoveLast
  End Sub

  Public Function FindByCustomerID(CustomerID As String) As Boolean
   注释:Uses the Find method to locate customers
   注释:with a matching CustomerID.
   注释:Returns True value is customer(s) found
   Dim varBookmark As Variant
   rs.MoveFirst
   rs.Find ("CustomerID=注释:" & CustomerID & "注释:")
   If rs.EOF = True Then
     FindByCustomerID = False
     rs.Bookmark = varBookmark
   Else
     FindByCustomerID = True
   End If
  End Function

  Public Property Get EOF() As Boolean
  注释:Example of a read-only property
  No Property Lets here
  EOF = rs.EOF
  End Property
  Public Property Get BOF() As Boolean
   注释:Another example of a read-only property
   BOF = rs.BOF
  End Property
  Private Sub rs_MoveComplete(ByVal adReason As ADODB.EventReasonEnum, _
       ByVal pError As ADODB.Error, adStatus As ADODB.EventStatusEnum, _
       ByVal pRecordset As ADODB.Recordset)

   注释:Reacts to the recordset MoveComplete
   注释:method - raises event with each move
   RaiseEvent RecordsetMove
  End Sub

  需要说明的是:迄今为止,我们仅仅是在一个类中添加代码。当然,也可以选择"Project"->"Add Class"菜单来向工程添加多个类,而且还可利用"collections"使这些类工作在一起。但是在这里,我们仍然想用一个类来处理一个数据表。

  将上述类的代码复制并粘贴到自己的类中,下一节将讨论该程序的编译。