Programming Microsoft Visual Basic .NET/Programming Microsoft Visual Basic .NET (Microsoft Press)(X08-78517)(2002).bin/setup/vbnet/04 class fundamentals/classesdemo/classes.vb

Text File | 2002-03-16 | 18.8 KB | 645 lines

' this class is used by the TestByrefPassing procedure
Class SampleClass
    Public Number As Double
End Class

' The first version of the Person class demonstrates properties, methods, indexers,
' read-only, write-only, and default properties

Class Person
    ' Visual Basic.NET classes can expose Public constants.
    Public Const DefaultPassword As String = "mypwd"

    ' Fields visible from outside the class
    Public FirstName As String
    Public LastName As String

    ' You can define up to four addresses for this person,
    ' from Address(0) to Address(3).
    Public Address(4) As String

    Overridable Function CompleteName(Optional ByVal title As String = "") As String
        ' Use the title, if provided.
        If title <> "" Then CompleteName = title & " "
        ' Append first and last name.
        CompleteName &= FirstName & " " & LastName
    End Function

    ' the BirthDate property

    Dim m_BirthDate As Date

    Property BirthDate() As Date
        Get
            Return m_BirthDate
        End Get
        Set(ByVal Value As Date)
            m_BirthDate = Value
        End Set
    End Property

    ' the Spouse property

    Private m_Spouse As Person

    Property Spouse() As Person
        Get
            Return m_Spouse
        End Get
        Set(ByVal Value As Person)
            m_Spouse = Value
        End Set
    End Property

    ' The Age property is read-only.

    ReadOnly Property Age() As Integer
        Get
            Return Year(Now) - Year(m_BirthDate)
        End Get
    End Property

    ' LoginDate is a write-only property.

    Dim m_LoginDate As Date

    WriteOnly Property LoginDate() As Date
        Set(ByVal Value As Date)
            m_LoginDate = Value
        End Set
    End Property

    ' an example of default property

    Dim m_Notes(10) As String

    ' The Attachment property takes an Integer argument.
    ' Note that this is also the default property.

    Default Property Notes(ByVal index As Integer) As String
        Get
            If index < 0 Or index > UBound(m_Notes) Then
                Throw New IndexOutOfRangeException("Invalid note index")
            End If
            Return m_Notes(index)
        End Get
        Set(ByVal Value As String)
            If index < 0 Or index > UBound(m_Notes) Then
                Throw New IndexOutOfRangeException("Invalid note index")
            End If
            m_Notes(index) = Value
        End Set
    End Property

    ' The GotMail event is used to demonstrate event inheritance

    Event GotMail(ByVal msgText As String)

    Sub NotifyNewMail(ByVal msgText As String)
        ' Let all listeners know that we got mail.
        RaiseEvent GotMail(msgText)
    End Sub

    ' The Father, Mother and AreBrothers method are used to
    ' demonstrate shared member inheritance

    Public Father As Person
    Public Mother As Person

    Shared Function AreBrothers(ByVal p1 As Person, ByVal p2 As Person) As Boolean
        Return (p1.Father Is p2.Father) Or (p1.Mother Is p2.Mother)
    End Function
End Class

' This second version of the Person class demonstrates overloaded constructors,
' read-only fields, and the Finalize method.

Class Person2
    ' a public read-only field that can be assigned only from inside the constructor.
    Public ReadOnly CreateTime As Date

    ' First version of constructors takes first and last name.

    Sub New(ByVal firstName As String, ByVal lastName As String)
        Me.FirstName = firstName
        Me.LastName = lastName
        ' Remember when this instance was created.
        CreateTime = Now()
    End Sub

    ' Second version takes complete name (e.g. "Joe Doe").

    Sub New(ByVal completeName As String)
        Dim i As Integer
        i = InStr(completeName, " ")
        ' Error if there are fewer than two words.
        If i = 0 Then Throw New ArgumentException("Invalid Name")
        ' Initialize main properties.
        Me.FirstName = RTrim(Left(completeName, i - 1))
        Me.LastName = LTrim(Mid(completeName, i + 1))
        ' Remember when this instance was created.
        CreateTime = Now()
    End Sub

    ' FirstName and LastName properties

    Private m_FirstName As String
    Private m_LastName As String

    Property FirstName() As String
        Get
            Return m_FirstName
        End Get
        Set(ByVal Value As String)
            If Value = "" Then
                Throw New ArgumentException("Invalid FirstName property")
            End If
            m_FirstName = Value
        End Set
    End Property

    Property LastName() As String
        Get
            Return m_LastName
        End Get
        Set(ByVal Value As String)
            If Value = "" Then
                Throw New ArgumentException("Invalid LastName property")
            End If
            m_LastName = Value
        End Set
    End Property

    ' the BirthDate property

    Dim m_BirthDate As Date

    Property BirthDate() As Date
        Get
            Return m_BirthDate
        End Get
        Set(ByVal Value As Date)
            m_BirthDate = Value
        End Set
    End Property

    ' CompleteName property is overridable

    Overridable Function CompleteName() As String
        ' Append first and last name.
        Return FirstName & " " & LastName
    End Function

    ' the class's Finalize method

    Protected Overrides Sub Finalize()
        ' use Debug because the Console object might be finalized at this point.
        Debug.WriteLine("Person " & Me.CompleteName() & " is being destroyed")
    End Sub

End Class

' This third version of the Person class demonstrates
' event trapping from an array of objects.

Class Person3
    Event GotEmail(ByVal p As Person3, ByVal msgText As String)

    Public FirstName As String
    Public LastName As String

    Sub New(ByVal firstName As String, ByVal lastName As String)
        Me.FirstName = firstName
        Me.LastName = lastName
    End Sub

    Function CompleteName() As String
        Return FirstName & " " & LastName
    End Function

    ' Send an email to this person.
    ' (In this demo it just raises a GotEmail event.)
    Sub SendEmail(ByVal msgText As String)
        ' Let the client know which object raised the event.
        RaiseEvent GotEmail(Me, msgText)
    End Sub
End Class

' This forth version of the Person class demonstrates events that follow
' Microsoft's syntax guidelines

Class Person4
    ' some basic properties, methods, and constructors
    Public FirstName As String
    Public LastName As String

    Sub New(ByVal firstName As String, ByVal lastName As String)
        Me.FirstName = firstName
        Me.LastName = lastName
    End Sub

    Function CompleteName() As String
        Return FirstName & " " & LastName
    End Function

    ' support for the Married event

    Event Married(ByVal sender As Object, ByVal e As System.EventArgs)

    Dim m_Spouse As Person4

    Property Spouse() As Person4
        Get
            Return m_Spouse
        End Get
        Set(ByVal Value As Person4)
            ' Raise an event only if this is a different object.
            If Not (m_Spouse Is Value) Then
                m_Spouse = Value
                ' You can use the Empty shared field to return a new
                ' empty EventArgs object
                RaiseEvent Married(Me, EventArgs.Empty)
            End If
        End Set
    End Property

    ' support for the GotGift event

    Event GotGift(ByVal sender As Object, ByVal e As GotGiftEventArgs)

    ' Clients call this method to give a gift to this person.
    Sub GiveGift(ByVal giver As Person4, ByVal description As String)
        ' (In this demo we just raise an event.)
        ' Create a GotGiftEventArgs object on-the-fly.
        RaiseEvent GotGift(Me, New GotGiftEventArgs(giver, description))
    End Sub

End Class

' auxiliary class used for the Person4's GotGift event.

Class GotGiftEventArgs
    Inherits System.EventArgs

    ' The additional fields exposed by this class.
    Public Giver As Person4
    Public GiftDescription As String

    ' A convenient constructor
    Sub New(ByVal giver As Person4, ByVal giftDescription As String)
        Me.Giver = giver
        Me.GiftDescription = giftDescription
    End Sub
End Class

' a class that demonstrate property values passed byref

Class ValueClass
    Private Value As Double

    ' A property that uses the Value field.
    Property DoubleValue() As Double
        Get
            Return Me.Value * 2
        End Get
        Set(ByVal newValue As Double)
            Me.Value = newValue / 2
        End Set
    End Property
End Class


' The Widget class demonstrates the IDisposable interface.

Class Widget
    Implements IDisposable

    Sub Dispose() Implements IDisposable.Dispose
        ' Close files and release other resources here.
        ' ...
    End Sub
End Class

' The DataFile class demonstrates the Dispose+Finalize methods working in concert.
' The approach used is based on the cleanedUp private variable.

Class DataFile
    Implements IDisposable

    ' The file handle
    Private handle As Integer

    Sub New(ByVal inputFile As String)
        ' Open a file when the object is created.
        handle = FreeFile()
        FileOpen(handle, inputFile, OpenMode.Input)
    End Sub

    Sub Close()
        If handle <> 0 Then
            FileClose(handle)
            handle = 0
        End If
    End Sub

    ' True if clean-up code has run already.
    Private disposed As Boolean

    Sub Dispose() Implements IDisposable.Dispose
        Console.WriteLine("Dispose method")
        ' Clean up this object by running the Finalize method.
        Finalize()
    End Sub

    Protected Overrides Sub Finalize()
        Console.WriteLine("Finalize method")
        ' Run clean-up code only if not done already.
        If Not disposed Then
            ' Close the file if it is still open.
            Close()
            ' Perform other clean-up chores.
            ' ...
            ' Remember that clean-up code has run.
            disposed = True
        End If
    End Sub
End Class

' The second version of the DataFile class uses the GC.SuppressFinalize
' method for optimized clean-up code.

Class DataFile2
    Implements IDisposable

    ' The file handle
    Private handle As Integer

    ' Open a file, store its handle.
    Sub Open(ByVal inputFile As String)
        ' Throw an exception if the object has been already disposed.
        If disposed Then Throw New ObjectDisposedException("DataFile2")
        ' Continue with regular operations.
        handle = FreeFile()
        FileOpen(handle, inputFile, OpenMode.Input)
    End Sub

    ' Close the file, don't throw an exception if already closed.
    Sub Close()
        ' Throw an exception if the object has been already disposed.
        If disposed Then Throw New ObjectDisposedException("DataFile2")
        ' Continue with regular operations.
        If handle <> 0 Then
            FileClose(handle)
            handle = 0
        End If
    End Sub

    ' This private variable is True if the object has been disposed.
    Dim disposed As Boolean

    Sub Dispose() Implements IDisposable.Dispose
        Debug.WriteLine("Dispose method")
        ' Execute the code that does the clean up.
        Dispose(True)
        ' Let the CLR know that Finalize doesn't have to be called.
        GC.SuppressFinalize(Me)
    End Sub

    Protected Overrides Sub Finalize()
        Debug.WriteLine("Finalize method")
        ' Execute the code that does the clean up.
        Dispose(False)
    End Sub

    ' This procedure is where the actual cleanup occurs.
    Protected Overridable Sub Dispose(ByVal disposing As Boolean)
        ' Exit now if the object has been already disposed.
        If disposed Then Exit Sub

        If disposing Then
            ' The object is being disposed, not finalized.
            ' It is safe to access other objects (other than the base
            ' object) only from inside this block.
        End If

        ' Perform clean up chores that have to be executed in either case.
        Close()

        ' Remember that the object has been disposed.
        disposed = True
    End Sub
End Class

' The PrimeNumbers class demonstrates weakly-referenced objects.

Class PrimeNumbers
    ' IsPrime(n) contains True if n is prime, False otherwise
    Public IsPrime() As Boolean

    ' The constructor evaluates "primeness" for the first N integers.
    Sub New(ByVal maxPrimeNumber As Integer)
        ReDim IsPrime(maxPrimeNumber)
        Dim i, j As Integer

        ' For debugging purposes
        Console.WriteLine("Initializing PrimeNumbers")

        ' A rather inefficient algorithm (hey, it's just a demo).
        ' Start assuming that all numbers are prime.
        For i = 1 To maxPrimeNumber
            IsPrime(i) = True
        Next

        ' Next, visit all items, starting at IsPrime(2).
        For i = 2 To maxPrimeNumber
            ' If this number is prime, then all its multiple aren't prime.
            If IsPrime(i) Then
                For j = i * 2 To maxPrimeNumber Step i
                    IsPrime(j) = False
                Next
            End If
        Next
    End Sub
End Class

' The Logger class demonstrates WithEvents and AddHandler keywords

Class Logger
    Event LogAction(ByVal actionName As String)

    Sub OpenFile()
        RaiseEvent LogAction("OpenFile")
    End Sub

    Sub ReadData()
        RaiseEvent LogAction("ReadData")
    End Sub

    Sub CloseFile()
        RaiseEvent LogAction("CloseFile")
    End Sub

    Protected Overrides Sub Finalize()
        RaiseEvent LogAction("Finalize")
    End Sub
End Class

' The Invoice class demonstrates shared members.

Class Invoice
    ' This variable holds the number of instances created so far.
    Shared InstanceCount As Integer

    ' A unique ID for this instance.
    Public ReadOnly Id As Long

    Sub New()
        ' Increment number of created instances.
        InstanceCount += 1
        ' Use the current count as the ID for this instance.
        Id = InstanceCount
        ' ...
    End Sub
End Class

' The SerialPort class demonstrates the use of shared fields and methods

Class SerialPort
    Implements IDisposable

    ' This array is shared by all instances of the class.
    ' (This examples assumes that 4 ports are available.)
    Public Shared AllocatedPorts(3) As Boolean

    ' Return the number of the first available serial port.
    Shared Function GetAvailablePort() As Short
        Dim i As Short
        For i = 0 To 3
            If AllocatedPorts(i) = False Then
                ' This port is still available.
                GetAvailablePort = i
                Exit For
            End If
            ' Return û1 if no port is available.
            GetAvailablePort = -1
        Next
    End Function

    ' The serial port used by this instance (in the range 0-3).
    Public ReadOnly Port As Short

    Sub New()
        Port = GetAvailablePort()
        ' throw a (generic) exception if no port is available
        If Port < 0 Then Throw New Exception()
        ' Mark the port as unavailable.
        AllocatedPorts(Port) = True
    End Sub

    ' Mark the port as available when this instance is destroyed.
    Sub Dispose() Implements IDisposable.Dispose
        AllocatedPorts(Port) = False
    End Sub
End Class

' The Triangle class demonstrates using shared members

Class Triangle
    Shared Event InvalidTriangle(ByVal side1 As Double, ByVal side2 As Double, ByVal side3 As Double)
    Event DummyEvent()

    Shared Function GetPerimeter(ByVal side1 As Double, _
        ByVal side2 As Double, ByVal side3 As Double) As Double
        If side1 < side2 + side3 And side1 > Math.Abs(side2 - side3) Then
            Return side1 + side2 + side3
        Else
            ' Pass Nothing when the event is raised from inside
            ' a shared method.
            RaiseEvent InvalidTriangle(side1, side2, side3)
        End If
    End Function

    Shared Function GetArea(ByVal side1 As Double, _
        ByVal side2 As Double, ByVal side3 As Double) As Double

        If side1 < side2 + side3 And side1 > Math.Abs(side2 - side3) Then
            ' First, evaluate half of the perimeter.
            Dim halfP As Double = (side1 + side2 + side3) / 2
            ' Then apply the Heron formula.
            Return (halfP * (halfP - side1) * (halfP - side2) * (halfP - side3)) ^ 0.5
        Else
            ' Pass Nothing when the event is raised from inside
            ' a shared method.
            RaiseEvent InvalidTriangle(side1, side2, side3)
        End If
    End Function

    ' The tree sides
    Public Side1 As Double
    Public Side2 As Double
    Public Side3 As Double

    ' The Perimeter instance property
    ReadOnly Property Perimeter() As Double
        Get
            If Side1 < Side2 + Side3 And Side1 > Math.Abs(Side2 - Side3) Then
                Return Side1 + Side2 + Side3
            Else
                RaiseEvent InvalidTriangle(Side1, Side2, Side3)
            End If
        End Get
    End Property

    ' The Area instance property
    ReadOnly Property Area() As Double
        Get
            If Side1 < Side2 + Side3 And Side1 > Math.Abs(Side2 - Side3) Then
                ' First, evaluate half of the perimeter.
                Dim halfP As Double = (Side1 + Side2 + Side3) / 2
                ' Then apply the Heron formula.
                Return (halfP * (halfP - Side1) * (halfP - Side2) * (halfP - Side3)) ^ 0.5
            Else
                RaiseEvent InvalidTriangle(Side1, Side2, Side3)
            End If
        End Get
    End Property

End Class

' The FileLogger class demonstrates shared constructors

Class FileLogger
    Shared FileHandle As Integer

    ' a readonly shared member
    Public Shared ReadOnly StartExecutionTime As Date = Now()
    Public Shared ReadOnly InitialDir As String

    ' The shared constructor
    Shared Sub New()
        ' Open the log file before the first object from
        ' this class is instantiated.
        FileHandle = FreeFile()
        FileOpen(FileHandle, "C:\data.log", OpenMode.Output)

        InitialDir = System.IO.Directory.GetCurrentDirectory
    End Sub

    ' a shared method that closes the log file
    Shared Sub Close()
        FileClose(FileHandle)
    End Sub

    Sub New()
        ' Here goes the initialization code for a specific instance.
        ' ...
    End Sub

    Sub Log(ByVal Text As String)
        PrintLine(FileHandle, Text)
    End Sub
End Class