Programming Microsoft Visual Basic .NET/Programming Microsoft Visual Basic .NET (Microsoft Press)(X08-78517)(2002).bin/setup/vbnet/06 interfaces and delegates/interfacesdemo/classes.vb

Text File | 2002-03-16 | 17.2 KB | 540 lines

' the Person class demonstrates the IComparable interface

Class Person
    Implements IComparable

    ' Public fields
    Public FirstName As String
    Public LastName As String

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

    ' A property that returns the name in the format "Doe, Joe".
    ReadOnly Property ReverseName() As String
        Get
            Return LastName & ", " & FirstName
        End Get
    End Property

    ' This procedure add sorting capabilities to the class.
    Private Function CompareTo(ByVal obj As Object) As Integer _
        Implements IComparable.CompareTo
        ' Null objects always come before anything else.
        If obj Is Nothing Then Return 1

        ' Cast to a specific Person object, to avoid late binding.
        Dim other As Person = CType(obj, Person)
        ' Use StrComp to simplify case-insensitive comparisons.
        Return StrComp(ReverseName, other.ReverseName, CompareMethod.Text)
    End Function
End Class

' this  version of the Person class demonstrates the IComparer interface

Class Person2
    ' Public fields
    Public FirstName As String
    Public LastName As String

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

    ' A property that returns name in the format "Joe Doe".
    ReadOnly Property CompleteName() As String
        Get
            Return FirstName & " " & LastName
        End Get
    End Property

    ' A property that returns name in the format "Doe, Joe".
    ReadOnly Property ReverseName() As String
        Get
            Return LastName & ", " & FirstName
        End Get
    End Property

    ' Shared methods that return an auxiliary object.
    Shared Function CompareByName() As IComparer
        Return New ComparerByName()
    End Function

    Shared Function CompareByReverseName() As IComparer
        Return New ComparerByReverseName()
    End Function

    ' First auxiliary class, to sort on CompleteName.
    Class ComparerByName
        Implements IComparer

        Function Compare(ByVal o1 As Object, ByVal o2 As Object) _
            As Integer Implements IComparer.Compare
            ' Cast both objects to Person and do the comparison.
            Dim p1 As Person2 = CType(o1, Person2)
            Dim p2 As Person2 = CType(o2, Person2)
            Return StrComp(p1.CompleteName, p2.CompleteName, _
                CompareMethod.Text)
        End Function
    End Class

    ' Second auxiliary class, to sort on ReverseName.
    Class ComparerByReverseName
        Implements IComparer

        Function Compare(ByVal o1 As Object, ByVal o2 As Object) _
            As Integer Implements IComparer.Compare
            ' Save code by casting to Person objects on the fly.
            Return StrComp(CType(o1, Person2).ReverseName, _
                DirectCast(o2, Person2).ReverseName, CompareMethod.Text)
        End Function
    End Class
End Class


' The IPluggableAddin and IHostEnvironment interfaces are implemented by the MyAddin class

Interface IPluggableAddin
    Event Connected()

    ReadOnly Property Id() As Long

    Property State() As Boolean

    Function OnConnection(ByVal environment As String) As Boolean

    Sub OnDisconnection()

    Class PluginClass
        ' an example of a class nested in an interface
    End Class

End Interface

' Another interface with just one property
Interface IHostEnvironment
    ReadOnly Property HashCode() As Long
End Interface


' The MyAddin class implements the IPluggableAddin interface

Public Class MyAddin
    ' You can have two distinct Implements statements, if you prefer so.
    Implements IPluggableAddin, IHostEnvironment

    ' this class exposes the IDisposable interface
    Implements IDisposable

    ' The following procedure implements two read-only properties
    ' from distinct interfaces.
    ReadOnly Property Id() As Long Implements IPluggableAddin.Id, IHostEnvironment.HashCode
        Get
            ' ...
        End Get
    End Property


    Private Property State() As Boolean Implements IPluggableAddin.State
        Get
            ' ...
        End Get
        Set(ByVal Value As Boolean)
            ' ...
        End Set
    End Property

    Protected Overridable Function OnConnection(ByVal Environment As String) _
        As Boolean Implements IPluggableAddin.OnConnection
        ' ...
    End Function

    Private Sub OnDisconnection() Implements IPluggableAddin.OnDisconnection
        ' ...
    End Sub

    ' Dispose should always be defined as Overridable.
    Overridable Sub Dispose() Implements IDisposable.Dispose
        Console.WriteLine("Dispose method in MyAddin class")
    End Sub

    Event Connected() Implements InterfacesDemo.IPluggableAddin.Connected
End Class

' the AnotherAddin class demonstrates that interfaces are inherited in derived classes

' This class inherits all the interfaces defined in MyAddin class.
Class AnotherAddin
    Inherits MyAddin

    Protected Overrides Function OnConnection(ByVal Environment As String) As Boolean
        ' ...
    End Function

    Overrides Sub Dispose()
        ' Clean-up code for the AnotherAddin class
        ' ...(omitted)...
        Console.WriteLine("Dispose method in AnotherAddin class")

        ' Complete the clean-up step by calling the base class's Dispose.
        MyBase.Dispose()
    End Sub

End Class

' This is a simple interface with one function

Interface IGetObjectRef
    Function GetObjectRef() As Object
End Interface

' This is a structure that implements an interface
Structure MyStruct
    Implements IGetObjectRef

    Dim x As Integer

    Public Function GetObjectRef() As Object Implements InterfacesDemo.IGetObjectRef.GetObjectRef
        Return Me
    End Function
End Structure

' A class for doing case-insensitive string comparisons the VB6 way

Class CaseInsensitiveComparerVB6
    Implements IComparer

    Public Function Compare(ByVal o1 As Object, ByVal o2 As Object) As Integer Implements System.Collections.IComparer.Compare
        Return StrComp(o1.ToString, o2.ToString, CompareMethod.Binary)
    End Function
End Class

' The WordParser class and its nested class demonstrate the IEnumerable and IEnumerator interfaces

Class WordParser
    ' This Implements statement means that this class supports For Each.
    Implements IEnumerable

    ' The sentence being parsed
    Public Source As String

    ' A simple constructor
    Sub New(ByVal source As String)
        Me.Source = source
    End Sub

    ' This function is called when a For Each is encountered.
    ' It must return an object that supports the IEnumerator interface.
    Function GetEnumerator() As IEnumerator Implements IEnumerable.GetEnumerator
        ' Return an instance of the nested class.
        Return New WordParserEnumerator(Source)
    End Function

    ' The nested class that supports IEnumerator.
    Class WordParserEnumerator
        ' This Implements statement ensures that this class can be used
        ' to enumerate items in a For Each.
        Implements IEnumerator

        ' The sentence being parsed (passed in the constructor)
        Dim Source As String
        ' This index is used to visit all the characters in the sentence.
        Dim CharIndex As Integer
        ' The current word
        Dim CurrentWord As String

        ' The outer class passes the Source string through this constructor.
        Sub New(ByVal Source As String)
            Me.Source = Source
            ' Reset CharIndex.
            Reset()
        End Sub

        ' Reset the counter.
        ' Note that Visual Basic.NET does *not* call this method when a For
        ' Each loop starts, so you must call it in this class's constructor.
        Private Sub Reset() Implements IEnumerator.Reset
            CharIndex = 0
        End Sub

        ' This property returns the current element.
        Private ReadOnly Property Current() As Object _
            Implements IEnumerator.Current
            Get
                ' When VB.NET calls this property, the MoveNext method
                ' has already found the current word.
                Return CurrentWord
            End Get
        End Property

#Const USE_REGEX = True

#If Not USE_REGEX Then

        ' This function advances the pointer and returns True if a new word
        ' has been found, False otherwise.
        Private Function MoveNext() As Boolean Implements IEnumerator.MoveNext
            ' Advance CharIndex if it is currently pointing to a separator.
            Do While CharIndex < Len(Source) And _
                IsSeparator(Mid(Source, CharIndex + 1, 1))
                CharIndex += 1
            Loop
            ' Return False if there are no more characters.
            If CharIndex >= Len(Source) Then Return False

            ' Remember current position of index.
            Dim StartIndex As Integer = CharIndex

            ' Continue to loop until we find another separator.
            Do While CharIndex < Len(Source) And _
                Not IsSeparator(Mid(Source, CharIndex + 1, 1))
                CharIndex += 1
            Loop

            ' We found a new word.
            CurrentWord = Mid(Source, StartIndex + 1, CharIndex - StartIndex)
            ' Return True to signal success.
            Return True
        End Function

        ' Auxiliary function that determines whether a char is a separator.
        Private Function IsSeparator(ByVal c As String) As Boolean
            Return InStr(" ,.:;!?", c) > 0
        End Function
#Else
        ' This regular expression searches for words
        Dim re As New System.Text.RegularExpressions.Regex("\w+")

        ' This function advances the pointer and returns True if a new word
        ' has been found, False otherwise.
        Private Function MoveNext() As Boolean Implements IEnumerator.MoveNext
            ' find the next word.
            Dim ma As System.Text.RegularExpressions.Match
            ma = re.Match(Source, CharIndex)

            ' Return False if there are no more characters.
            If Not ma.Success Then Return False

            ' We found a new word.
            CurrentWord = ma.Value

            ' Remember current position of index.
            CharIndex = ma.Index + ma.Length

            ' Return True to signal success.
            Return True
        End Function
#End If

    End Class
End Class

' an example of a cloneable class

Class Employee
    Implements ICloneable

    Public FirstName As String
    Public LastName As String
    Public Boss As Employee

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

#Const USE_MEMBERWISECLONE = True

    ' The only method of the ICloneable interface
    Public Function Clone() As Object Implements ICloneable.Clone

#If USE_MEMBERWISECLONE Then
        ' this is the easy way for doing shallow copying
        Return Me.MemberwiseClone

#Else

        ' this block of code shows how to do "manual cloning".

        ' Create a new Employee with same property values.
        Dim e As New Employee(FirstName, LastName)
        ' Properties not accepted in the constructors must be copied manually.
        e.Boss = Me.Boss
        Return e
#End If

    End Function
End Class

' an improved example of a clonable class

Class Employee2
    Implements ICloneable

    Public FirstName As String
    Public LastName As String
    Public Boss As Employee2

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

    ' The only method of the ICloneable interface
    Public Function Clone() As Object Implements ICloneable.Clone
        ' Start creating a shallow copy of this object.
        ' (This copies all non-object properties in one operation)
        Dim e As Employee2 = DirectCast(Me.MemberwiseClone, Employee2)

        ' manually copy the Boss property, reusing its Clone method.
        If Not (e.Boss Is Nothing) Then
            e.Boss = DirectCast(Me.Boss.Clone, Employee2)
        End If
        Return e
    End Function

End Class

' a cloneable class that uses a strongly typed Clone method.

Class Employee3
    Implements ICloneable

    Public FirstName As String
    Public LastName As String
    Public Boss As Employee3

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

    ' The only method of the ICloneable interface (private)
    Private Function CloneMe() As Object Implements ICloneable.Clone
        ' reuses the code in the strong-typed Clone method
        Return Clone()
    End Function

    Function Clone() As Employee3
        ' Start creating a shallow copy of this object.
        ' (This copies all non-object properties in one operation)
        Clone = CType(Me.MemberwiseClone, Employee3)
        ' manually copy the Boss property, reusing its Clone method.
        If Not (Clone.Boss Is Nothing) Then
            Clone.Boss = Me.Boss.Clone
        End If
    End Function
End Class

' this class shows how to support IEnumerable interface
' it provides access to all files in a directory tree

Class FileTree
    Implements IEnumerable

    ' the search path
    Public ReadOnly DirPath As String

    ' the constructor
    Sub New(ByVal DirPath As String)
        Me.DirPath = DirPath
    End Sub

    ' return an Enumerable object
    Function GetEnumerator() As IEnumerator Implements IEnumerable.GetEnumerator
        Return New FileTreeEnumerator(DirPath)
    End Function

    ' the IEnumerator private object
    Class FileTreeEnumerator
        Implements IEnumerator

        Dim DirPath As String

        ' this contains the Enumerator object for the file list in current dir
        Dim FileEnumerator As IEnumerator
        ' these contain the stack of the Enumerator objects
        ' for subdirectories of all pending directories
        Dim DirEnumerators As New Stack()

        Sub New(ByVal DirPath As String)
            ' save the directory path
            Me.DirPath = DirPath
            Reset()
        End Sub

        Sub Reset() Implements IEnumerator.Reset
            ' the DirectoryInfo object that represents the root object
            Dim di As New System.IO.DirectoryInfo(DirPath)

            ' get the Enumerator object for the file list, and reset it
            FileEnumerator = di.GetFiles.GetEnumerator
            FileEnumerator.Reset()

            ' get the Enumerator object for subdir list and reset it
            Dim dirEnum As IEnumerator = di.GetDirectories.GetEnumerator
            dirEnum.Reset()
            ' push it onto the stack
            DirEnumerators.Push(dirEnum)
        End Sub

        Function MoveNext() As Boolean Implements IEnumerator.MoveNext
            ' Simply delegate to the File Enumerator object
            If FileEnumerator.MoveNext Then
                ' it returned True, so we can exit
                Return True
            End If

            ' if there are no files in the current directory, check whether
            ' there is another subdir in the current directory

            ' first, get the current directory enumerator
            Dim dirEnum As IEnumerator = CType(DirEnumerators.Peek, IEnumerator)

            ' check whether the current subdir enumerator has items
            Do Until dirEnum.MoveNext
                ' there are no more subdirs at this level, so we must pop
                ' another element of the stack
                DirEnumerators.Pop()

                If DirEnumerators.Count = 0 Then
                    ' Return False if there are no more subdirs to parse
                    Return False
                End If

                ' get the current enumerator
                dirEnum = CType(DirEnumerators.Peek, IEnumerator)
            Loop

            ' we can create a DirectoryInfo
            Dim di As System.IO.DirectoryInfo = CType(dirEnum.Current, System.IO.DirectoryInfo)

            ' store the file enumerator and reset it
            FileEnumerator = di.GetFiles.GetEnumerator
            FileEnumerator.Reset()

            ' get the Enumerator object for subdir list and reset it
            dirEnum = di.GetDirectories.GetEnumerator
            dirEnum.Reset()
            ' push it onto the stack
            DirEnumerators.Push(dirEnum)

            ' recursively call this routine, in order to process the file enumerator
            Return Me.MoveNext

        End Function

        ' The current property simply delegates to FileEnumerator.Current
        ReadOnly Property Current() As Object Implements IEnumerator.Current
            Get
                Return FileEnumerator.Current
            End Get
        End Property

    End Class
End Class