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OnSerializingAttribute Class

When applied to a method, specifies that the method is called before serialization of an object.

Namespace:  System.Runtime.Serialization
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
<ComVisibleAttribute(True)> _
<AttributeUsageAttribute(AttributeTargets.Method, Inherited := False)> _
Public NotInheritable Class OnSerializingAttribute _
	Inherits Attribute
'Usage
Dim instance As OnSerializingAttribute

Use the OnSerializingAttribute to manipulate the object before serialization occurs.

To use the OnSerializingAttribute, the method must contain a StreamingContext parameter. The attribute marks the method to be called by the serialization infrastructure and the StreamingContext provides additional data about the type of serialization taking place. The usage is shown in the following code:

' Visual Basic
<OnSerializingAttribute()> _
Private Sub RunThisMethod(context As StreamingContext)
    ' Code not shown.
End Sub
NoteNote:

In your code, you can use the word OnSerializing instead of the longer OnSerializingAttribute.

The following example applies the OnDeserializedAttribute, OnSerializingAttribute, OnSerializedAttribute, and OnDeserializingAttribute attributes to methods in a class.

Imports System
Imports System.IO
Imports System.Runtime.Serialization
Imports System.Runtime.Serialization.Formatters.Binary

Public Class Test
    Public Shared Sub Main()
        ' Create a new TestSimpleObject object. 
        Dim obj As New TestSimpleObject()

        Console.WriteLine(vbLf + " Before serialization the object contains: ")
        obj.Print()

        ' Open a file and serialize the object into binary format. 
        Dim stream As Stream = File.Open("DataFile.dat", FileMode.Create)
        Dim formatter As New BinaryFormatter()

        Try
            formatter.Serialize(stream, obj)

            ' Print the object again to see the effect of the  
            'OnSerializedAttribute.
            Console.WriteLine(vbLf + " After serialization the object contains: ")
            obj.Print()

            ' Set the original variable to null.
            obj = Nothing
            stream.Close()

            ' Open the file "DataFile.dat" and deserialize the object from it.
            stream = File.Open("DataFile.dat", FileMode.Open)

            ' Deserialize the object from the data file.
            obj = CType(formatter.Deserialize(stream), TestSimpleObject)

            Console.WriteLine(vbLf + " After deserialization the object contains: ")
            obj.Print()
            Console.ReadLine()
        Catch se As SerializationException
            Console.WriteLine("Failed to serialize. Reason: " + se.Message)
            Throw 
        Catch exc As Exception
            Console.WriteLine("An exception occurred. Reason: " + exc.Message)
            Throw 
        Finally
            stream.Close()
            obj = Nothing
            formatter = Nothing 
        End Try 
    End Sub 
End Class 


' This is the object that will be serialized and deserialized.
<Serializable()> _
Public Class TestSimpleObject
    ' This member is serialized and deserialized with no change. 
    Public member1 As Integer 

    ' The value of this field is set and reset during and  
    ' after serialization. 
    Private member2 As String 

    ' This field is not serialized. The OnDeserializedAttribute  
    ' is used to set the member value after serialization.
    <NonSerialized()> _
    Public member3 As String 

    ' This field is set to null, but populated after deserialization. 
    Private member4 As String 

    ' Constructor for the class. 
    Public Sub New()
        member1 = 11
        member2 = "Hello World!"
        member3 = "This is a nonserialized value"
        member4 = Nothing 
    End Sub 

    Public Sub Print()
        Console.WriteLine("member1 = '{0}'", member1)
        Console.WriteLine("member2 = '{0}'", member2)
        Console.WriteLine("member3 = '{0}'", member3)
        Console.WriteLine("member4 = '{0}'", member4)
    End Sub

    <OnSerializing()> _
    Friend Sub OnSerializingMethod(ByVal context As StreamingContext)
        member2 = "This value went into the data file during serialization." 
    End Sub

    <OnSerialized()> _
    Friend Sub OnSerializedMethod(ByVal context As StreamingContext)
        member2 = "This value was reset after serialization." 
    End Sub

    <OnDeserializing()> _
    Friend Sub OnDeserializingMethod(ByVal context As StreamingContext)
        member3 = "This value was set during deserialization" 
    End Sub

    <OnDeserialized()> _
    Friend Sub OnDeserializedMethod(ByVal context As StreamingContext)
        member4 = "This value was set after deserialization." 
    End Sub 
End Class 

' Output: 
'  Before serialization the object contains:  
' member1 = '11' 
' member2 = 'Hello World!' 
' member3 = 'This is a nonserialized value' 
' member4 = '' 

'  After serialization the object contains:  
' member1 = '11' 
' member2 = 'This value was reset after serialization.' 
' member3 = 'This is a nonserialized value' 
' member4 = '' 

'  After deserialization the object contains:  
' member1 = '11' 
' member2 = 'This value went into the data file during serialization.' 
' member3 = 'This value was set during deserialization' 
' member4 = 'This value was set after deserialization.'

System.Object
  System.Attribute
    System.Runtime.Serialization.OnSerializingAttribute

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0

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