........
只要确保Desk类别的指令──
dSize = Room.GetMother().GetSize() * 0.18
是在MyRoom类别的指令──
rSize = 100
之后执行即可了。
上述的子对象是透过Shared 程序来取得母对象的参考值﹐然后才跟母对象沟通。如果不透过Shared程序，也可以采取下述方法：
''''ex04.bas
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
''''----------------------------------------------------
Class Room
Protected rSize As Double
Public Overridable Sub Create()
End Sub
Public Function GetSize() As Double
GetSize = rSize
End Function
End Class
Class Desk
Protected dSize As Double
Protected myMother As Room
Public Sub Create(ByVal mo As Room)
myMother = mo
dSize = myMother.GetSize() * 0.18
End Sub
Public Function GetSize() As Double
GetSize = dSize
End Function
End Class
''''----------------------------------------------------
Class MyRoom
Inherits Room
Private rd As Desk
Public Sub New()
rd = New Desk()
Me.Create()
End Sub
Public Overrides Sub Create()
rSize = 100
rd.Create(Me)
End Sub
Public Sub Show()
MessageBox.Show("Room Size: " str(rSize))
MessageBox.Show("Desk Size: " str(rd.GetSize()))
End Sub
End Class
''''----------------------------------------------------
Public Class Form1
Inherits System.WinForms.Form
Public Sub New()
MyBase.New()
Form1 = Me
''''This call is required by the Win Form Designer.
InitializeComponent()
''''TODO: Add any initialization after the InitializeComponent() call
End Sub
''''Form overrides dispose to clean up the component list.
Public Overrides Sub Dispose()
MyBase.Dispose()
components.Dispose()
End Sub
#Region " Windows Form Designer generated code "
......
#End Region
Protected Sub Form1_Click(ByVal sender As Object,
ByVal e As System.EventArgs)
Dim r As New MyRoom()
r.Show()
End Sub
End Class
此程序输出：
Room Size: 100
Desk Size: 18
Desk之对象含个参考 myMother ﹐指向其母对象。这项关系是在母子对象皆建好时﹐才由Create()程序所建立的。于是﹐建立出母子对象之关系﹕
综上所述，当MyRoom类别使用如下指令──
Private rd As New Desk()
时，才必须把New()与Create()分离。如果使用如下指令──
Private rd As Desk
Public Sub New()
rd = New Desk()
.....
End Sub
就不必分离了，原因是：New()与Create()的执行顺序是一致的，例如两者可合并如下的VB程序：
''''ex05.bas
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
''''----------------------------------------------------
Class Room
Protected rSize As Double
Public Function GetSize() As Double
GetSize = rSize
End Function
End Class
Class Desk
Protected dSize As Double
Protected myMother As Room
Public Sub New(ByVal mo As Room)
myMother = mo
dSize = myMother.GetSize() * 0.18
End Sub
Public Function GetSize() As Double
GetSize = dSize
End Function
End Class
''''----------------------------------------------------
Class MyRoom
Inherits Room
Private rd As Desk
Public Sub New()
rSize = 100
rd = New Desk(Me)
End Sub
Public Sub Show()
MessageBox.Show("Room Size: " str(rSize))
MessageBox.Show("Desk Size: " str(rd.GetSize()))
End Sub
End Class
''''----------------------------------------------------
Public Class Form1
Inherits System.WinForms.Form
Public Sub New()
MyBase.New()
Form1 = Me
''''This call is required by the Win Form Designer.
InitializeComponent()
''''TODO: Add any initialization after the InitializeComponent() call
End Sub
''''Form overrides dispose to clean up the component list.
Public Overrides Sub Dispose()
MyBase.Dispose()
components.Dispose()
End Sub
#Region " Windows Form Designer generated code "
......
#End Region
Protected Sub Form1_Click(ByVal sender As Object,
ByVal e As System.EventArgs)
Dim r As New MyRoom()
r.Show()
End Sub
End Class
此程序输出：
Room Size: 100
Desk Size: 18
3. 特类别继承与母子对象
您已很熟悉父子类别关系了﹐这继承关系的另一面是母子对象关系。例如﹐
''''ex06.bas
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
''''----------------------------------------------------
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