.NET Framework Class Library
OnSerializingAttribute Class

When applied to a method, specifies that the method is during serialization of an object in an object graph. The order of serialization relative to other objects in the graph is non-deterministic.

Inheritance Hierarchy
SystemObject
   SystemAttribute
    System.Runtime.SerializationOnSerializingAttribute

Namespace:   System.Runtime.Serialization
Assembly:  mscorlib (in mscorlib.dll)
Syntax
<[%$TOPIC/x4wddfsb_en-us_VS_110_2_0_0_0_0%]([%$TOPIC/x4wddfsb_en-us_VS_110_2_0_0_0_1%].Method, Inherited := False)> _
<[%$TOPIC/x4wddfsb_en-us_VS_110_2_0_0_0_2%](True)> _
Public NotInheritable Class OnSerializingAttribute _
	Inherits [%$TOPIC/x4wddfsb_en-us_VS_110_2_0_0_0_3%]
[[%$TOPIC/x4wddfsb_en-us_VS_110_2_0_1_0_0%]([%$TOPIC/x4wddfsb_en-us_VS_110_2_0_1_0_1%].Method, Inherited = false)]
[[%$TOPIC/x4wddfsb_en-us_VS_110_2_0_1_0_2%](true)]
public sealed class OnSerializingAttribute : [%$TOPIC/x4wddfsb_en-us_VS_110_2_0_1_0_3%]
[[%$TOPIC/x4wddfsb_en-us_VS_110_2_0_2_0_0%]([%$TOPIC/x4wddfsb_en-us_VS_110_2_0_2_0_1%]::Method, Inherited = false)]
[[%$TOPIC/x4wddfsb_en-us_VS_110_2_0_2_0_2%](true)]
public ref class OnSerializingAttribute sealed : public [%$TOPIC/x4wddfsb_en-us_VS_110_2_0_2_0_3%]
[<[%$TOPIC/x4wddfsb_en-us_VS_110_2_0_3_0_0%]>]
[<[%$TOPIC/x4wddfsb_en-us_VS_110_2_0_3_0_1%]([%$TOPIC/x4wddfsb_en-us_VS_110_2_0_3_0_2%].Method, Inherited = false)>]
[<[%$TOPIC/x4wddfsb_en-us_VS_110_2_0_3_0_3%](true)>]
type OnSerializingAttribute =  
    class 
        inherit [%$TOPIC/x4wddfsb_en-us_VS_110_2_0_3_0_4%] 
    end

The OnSerializingAttribute type exposes the following members.

Constructors
  NameDescription
Public method Supported by Portable Class Library Supported in .NET for Windows Store apps OnSerializingAttributeInitializes a new instance of the OnSerializingAttribute class.
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Properties
  NameDescription
Public property TypeIdWhen implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute.)
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Methods
  NameDescription
Public method Supported by Portable Class Library Supported in .NET for Windows Store apps EqualsInfrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.)
Public method Supported by Portable Class Library Supported in .NET for Windows Store apps GetHashCodeReturns the hash code for this instance. (Inherited from Attribute.)
Public method Supported by Portable Class Library Supported in .NET for Windows Store apps GetTypeGets the Type of the current instance. (Inherited from Object.)
Public method IsDefaultAttributeWhen overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute.)
Public method MatchWhen overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.)
Public method Supported by Portable Class Library Supported in .NET for Windows Store apps ToStringReturns a string that represents the current object. (Inherited from Object.)
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Explicit Interface Implementations
  NameDescription
Explicit interface implemetation Private method _AttributeGetIDsOfNamesMaps a set of names to a corresponding set of dispatch identifiers. (Inherited from Attribute.)
Explicit interface implemetation Private method _AttributeGetTypeInfoRetrieves the type information for an object, which can be used to get the type information for an interface. (Inherited from Attribute.)
Explicit interface implemetation Private method _AttributeGetTypeInfoCountRetrieves the number of type information interfaces that an object provides (either 0 or 1). (Inherited from Attribute.)
Explicit interface implemetation Private method _AttributeInvokeProvides access to properties and methods exposed by an object. (Inherited from Attribute.)
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Remarks

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:

<OnSerializing()> _
Private Sub SetValuesOnSerializing(ByVal context As StreamingContext)
    ' Code not shown. 
End Sub
[OnSerializing]
private void SetValuesOnSerializing(StreamingContext context)
{
    // Code not shown.
}
NoteNote

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

Examples

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.'
using System;
using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;

public class Test
{
    public static void Main()
    {
        // Create a new TestSimpleObject object.
        TestSimpleObject obj = new TestSimpleObject();

        Console.WriteLine("\n Before serialization the object contains: ");
        obj.Print();

        // Open a file and serialize the object into binary format.
        Stream stream = File.Open("DataFile.dat", FileMode.Create);
        BinaryFormatter formatter = new BinaryFormatter();

        try
        {
            formatter.Serialize(stream, obj);

            // Print the object again to see the effect of the  
            //OnSerializedAttribute.
            Console.WriteLine("\n After serialization the object contains: ");
            obj.Print();

            // Set the original variable to null.
            obj = null;
            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 = (TestSimpleObject)formatter.Deserialize(stream);

            Console.WriteLine("\n After deserialization the object contains: ");
            obj.Print();
            Console.ReadLine();
        }
        catch (SerializationException se)
        {
            Console.WriteLine("Failed to serialize. Reason: " + se.Message);
            throw;
        }
        catch (Exception exc)
        {
            Console.WriteLine("An exception occurred. Reason: " + exc.Message);
            throw;
        }
        finally
        {
            stream.Close();
            obj = null;
            formatter = null;
        }

    }
}


// This is the object that will be serialized and deserialized.
[Serializable()]
public class TestSimpleObject
{
    // This member is serialized and deserialized with no change. 
    public int member1;

    // The value of this field is set and reset during and  
    // after serialization. 
    private string member2;

    // This field is not serialized. The OnDeserializedAttribute  
    // is used to set the member value after serialization.
    [NonSerialized()]
    public string member3;

    // This field is set to null, but populated after deserialization. 
    private string member4;

    // Constructor for the class. 
    public TestSimpleObject()
    {
        member1 = 11;
        member2 = "Hello World!";
        member3 = "This is a nonserialized value";
        member4 = null;
    }

    public void Print()
    {
        Console.WriteLine("member1 = '{0}'", member1);
        Console.WriteLine("member2 = '{0}'", member2);
        Console.WriteLine("member3 = '{0}'", member3);
        Console.WriteLine("member4 = '{0}'", member4);
    }

    [OnSerializing()]
    internal void OnSerializingMethod(StreamingContext context)
    {
        member2 = "This value went into the data file during serialization.";
    }

    [OnSerialized()]
    internal void OnSerializedMethod(StreamingContext context)
    {
        member2 = "This value was reset after serialization.";
    }

    [OnDeserializing()]
    internal void OnDeserializingMethod(StreamingContext context)
    {
        member3 = "This value was set during deserialization";
    }

    [OnDeserialized()]
    internal void OnDeserializedMethod(StreamingContext context)
    {
        member4 = "This value was set after deserialization.";
    }
}

// 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.'
Version Information

.NET Framework

Supported in: 4.5.1, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1
Platforms

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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