VB.Net中文教程(1) 类别与封装性(4)
"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 a As New Tree()
a.input(2.1)
MessageBox.Show("OK")
End Sub
End Class
将input()摆在Tree类别中﹐为Tree之程序成员﹐它能存取资料成员height之值。把input()程序宣告为Public表示类别外之程序可藉来呼叫它﹐其呼叫格式为──
简单规则是﹕
Public 表示授权给外界之程序藉由此格式呼叫程序成员。
如果此程序改写为﹕
"ex09.bas
"Some Error Here!
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
"----------------------------------------------
Class Tree
Private varity As String
Private age As Integer
Private height As Single
Private Sub input(ByVal hei As Single)
height = hei
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 a As New Tree()
a.input(2.1)
MessageBox("OK")
End Sub
End Class
这程序有问题﹐因为 input()是Tree类别之Private程序成员而非Public程序成员﹐所以不能使用如下格式──
所以此程序错了。 请再看个例子吧﹗
"ex10.bas
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
"-------------------------------------------
Class Tree
Private varity As String
Private height As Single
Public age As Integer
Public Sub ShowAge()
MessageBox.Show("Age = " + str(Age))
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 a As New Tree()
a.age = 8
a.age = a.age + 2
a.ShowAge()
End Sub
End Class
Tree类别包含 2个Private成员── variety及height﹐且有 2个Public成员── age及 ShowAge()。由于age是Public资料成员﹐所以Fom1_Click()可使用格式──
来存取Tree内之age变量。指令── a.age = 8把8存入对象 a内之age 变量。指令──a.age = a.age + 2使对象a之age变量值加上2﹐成为10。由于ShowAge()程序是Public程序成员﹐也可使用格式──
来呼叫 ShowAge()程序。
由于类别（即对象）之目的是保护资料﹐并且提供程序成员来与外界沟通（接受、处理、并反应讯息）。通常﹐资料成员皆宣告为Private﹐而程序成员皆宣告为Public。亦即尽量少用格式──
而尽量多用格式──
例如﹕
"ex11.bas
Imports System.ComponentModel
Imports System.Drawing
Imports System.WinForms
"--------------------------------------------------------------------
Class Tree
Private varity As String
Private age As Integer
Private height As Single
Public Sub input(ByVal v As String, ByVal a As Integer, ByVal hei As Single)