Programming Microsoft Visual Basic .NET/Programming Microsoft Visual Basic .NET (Microsoft Press)(X08-78517)(2002).bin/setup/vbnet/11 object serialization/serializationdemo/classes.vb

Text File | 2002-03-16 | 8.9 KB | 267 lines

Imports System.Runtime.Serialization

' a serializable Person class

<Serializable()> _
Class Person
    Public FirstName As String
    Public LastName As String
    Private BirthDate As Date

    ' don't serialize this field, which can be easily recalculated
    <NonSerialized()> Private m_Age As Integer

    ' this field might cause circular references.
    Public Spouse As Person

    ' Note that BirthDate can be set only through the constructor method.
    Sub New(ByVal FirstName As String, ByVal LastName As String, _
        ByVal BirthDate As Date)
        Me.FirstName = FirstName
        Me.LastName = LastName
        Me.BirthDate = BirthDate
    End Sub

    ' The Age property caches its value in the m_Age private variable.

    ReadOnly Property Age() As Integer
        Get
            ' Evaluate the Age if not cached already.
            If m_Age = 0 Then m_Age = Year(Now) - Year(BirthDate)
            Return m_Age
        End Get
    End Property
End Class

' a class that supports custom serialization

<Serializable()> _
Class CompactDoubleArray
    Inherits ArrayList
    Implements ISerializable

    ' Elements that have this value aren't persisted.
    Public DefaultValue As Double

    ' We need this default constructor, otherwise the class
    ' couldn't be instantiated from regular clients.
    Sub New()
        MyBase.New()
    End Sub

    ' The special constructor implied by ISerializable.
    Private Sub New(ByVal info As SerializationInfo, _
        ByVal context As StreamingContext)

        ' Create the base ArrayList object.
        MyBase.New()
        ' Retrieve DefaultValue.
        DefaultValue = info.GetDouble("DefaultValue")
        ' Retrieve number of elements.
        Dim elCount As Integer = info.GetInt32("Count")

        Dim index As Integer, Value As Double
        For index = 0 To elCount - 1
            Try
                ' Try to assign the value in the SerializationInfo.
                Value = info.GetDouble(index.ToString)
            Catch
                ' If SerializeInfo doesn't contain that value,
                ' use the default value.
                Value = DefaultValue
            End Try
            ' Add the value to the inner ArrayList.
            MyBase.Add(Value)
        Next
    End Sub

    ' Serialize this object.
    Sub GetObjectData(ByVal info As SerializationInfo, _
        ByVal context As StreamingContext) _
        Implements ISerializable.GetObjectData

        ' Remember DefaultValue.
        info.AddValue("DefaultValue", DefaultValue)
        ' Remember the total number of elements.
        info.AddValue("Count", MyBase.Count)

        ' Serialize only elements whose value is different from DefaultValue.
        Dim index As Integer, Value As Double
        For index = 0 To MyBase.Count - 1
            ' The AddValue method requires a specific type.
            Value = CType(MyBase.Item(index), Double)
            If Value <> DefaultValue Then
                ' Store only if different from default value.
                info.AddValue(index.ToString, Value)
            End If
        Next
    End Sub
End Class

' a modified version of the class, that compacts data only when saving
' to a file or a remote machine

<Serializable()> _
Class CompactDoubleArray2
    Inherits ArrayList
    Implements ISerializable

    ' Elements that have this value aren't persisted.
    Public DefaultValue As Double

    ' We need this default constructor, otherwise the class
    ' couldn't be instantiated from regular clients.
    Sub New()
        MyBase.New()
    End Sub

    ' The special constructor implied by ISerializable.
    Private Sub New(ByVal info As SerializationInfo, ByVal context As StreamingContext)
        ' Create the base ArrayList object.
        MyBase.New()

        ' Attempt to get the serialized ArrayList.
        Try
            ' Try to read an element named ArrayList.
            Dim al As ArrayList
            al = DirectCast(info.GetValue("ArrayList", GetType(ArrayList)), ArrayList)
            ' If all went well, add to inner ArrayList and exit.
            MyBase.AddRange(al)
            Exit Sub
        Catch
            ' if failed, continue to extract elements.
        End Try

        ' Retrieve DefaultValue.
        DefaultValue = info.GetDouble("DefaultValue")
        ' Retrieve number of elements.
        Dim elCount As Integer = info.GetInt32("Count")

        Dim index As Integer, Value As Double
        For index = 0 To elCount - 1
            Try
                ' Try to assign the value in the SerializationInfo.
                Value = info.GetDouble(index.ToString)
            Catch
                ' If SerializeInfo doesn't contain that value,
                ' use the default value.
                Value = DefaultValue
            End Try
            ' Add the value to the inner ArrayList.
            MyBase.Add(Value)
        Next
    End Sub

    ' Serialize this object.
    Sub GetObjectData(ByVal info As SerializationInfo, ByVal context As StreamingContext) _
        Implements ISerializable.GetObjectData

        ' If not serializing to a file or a remote machine,
        ' then use non non-compact format.
        If context.State <> StreamingContextStates.File And context.State <> StreamingContextStates.CrossMachine Then
            ' Serialize the inner ArrayList and exit.
            info.AddValue("ArrayList", MyBase.Clone)
            Exit Sub
        End If

        ' Remember DefaultValue.
        info.AddValue("DefaultValue", DefaultValue)
        ' Remember the total number of elements.
        info.AddValue("Count", MyBase.Count)

        ' Serialize only elements whose value is different from DefaultValue.
        Dim index As Integer, Value As Double
        For index = 0 To MyBase.Count - 1
            ' The AddValue method requires a specific type.
            Value = CType(MyBase.Item(index), Double)
            If Value <> DefaultValue Then
                ' Store only if different from default value.
                info.AddValue(index.ToString, Value)
            End If
        Next
    End Sub
End Class

' A very simple serializable class
<Serializable()> Class Point
    Public X As Single
    Public Y As Single

    Sub New(ByVal X As Single, ByVal Y As Single)
        Me.X = X
        Me.Y = Y
    End Sub

    Overrides Function ToString() As String
        Return "(" & X.ToString & "," & Y.ToString & ")"
    End Function
End Class

' An array of Points that can serialize in a compact format
' provides an example of how to use IDeserializationCallback

<Serializable()> _
Class CompactPointArray
    Inherits ArrayList
    Implements ISerializable, IDeserializationCallback

    ' This variable cashes the object passed to the constructor.
    Dim m_info As SerializationInfo

    ' We need this constructor.
    Sub New()
        MyBase.New()
    End Sub

    ' The special constructor implied by ISerializable.
    Private Sub New(ByVal info As SerializationInfo, _
        ByVal context As StreamingContext)
        ' Create an ArrayList object.
        MyBase.New()
        ' Cache the SerializationInfo object.
        m_info = info
    End Sub

    ' This method is called when the object graph has been
    ' completely deserialized.
    Sub OnDeserialization(ByVal sender As Object) _
        Implements IDeserializationCallback.OnDeserialization
        ' Retrieve number of elements .
        Dim elCount As Integer = m_info.GetInt32("Count")

        Dim index As Integer, p As Point
        For index = 0 To elCount - 1
            Try
                ' Try to assign the value in the SerializationInfo.
                p = CType(m_info.GetValue(index.ToString, GetType(Point)), Point)
            Catch
                ' if any error, use a default "null" Point object
                p = New Point(0, 0)
            End Try
            ' Add to the inner ArrayList.
            MyBase.Add(p)
        Next
        ' We don't need this object any longer.
        m_info = Nothing
    End Sub

    ' Serialize only non-Nothing elements.
    Sub GetObjectData(ByVal info As SerializationInfo, ByVal _
        context As StreamingContext) Implements ISerializable.GetObjectData

        ' Remember the total number of elements.
        info.AddValue("Count", MyBase.Count)

        ' Serialize only elements whose value is different from (0,0).
        Dim index As Integer, p As Point
        For index = 0 To MyBase.Count - 1
            ' The AddValue method requires a specific type.
            p = DirectCast(MyBase.Item(index), Point)
            If p.X <> 0 Or p.Y <> 0 Then
                ' Add to SerializationInfo only if <> (0,0).
                info.AddValue(index.ToString, p)
            End If
        Next
    End Sub
End Class