OnSerializingAttribute Class
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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.

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


[AttributeUsageAttribute(AttributeTargets.Method, Inherited = false)]
public sealed class OnSerializingAttribute : Attribute


Initializes a new instance of the OnSerializingAttribute class.


When implemented in a derived class, gets a unique identifier for this Attribute.(Inherited from Attribute.)


This API supports the product infrastructure and is not intended to be used directly from your code. Returns a value that indicates whether this instance is equal to a specified object.(Inherited from Attribute.)


Returns the hash code for this instance.(Inherited from Attribute.)


Gets the Type of the current instance.(Inherited from Object.)


When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class.(Inherited from Attribute.)


When overridden in a derived class, returns a value that indicates whether this instance equals a specified object.(Inherited from Attribute.)


Returns a string that represents the current object.(Inherited from Object.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.GetIDsOfNames(Guid, IntPtr, UInt32, UInt32, IntPtr)

Maps a set of names to a corresponding set of dispatch identifiers.(Inherited from Attribute.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.GetTypeInfo(UInt32, UInt32, IntPtr)

Retrieves the type information for an object, which can be used to get the type information for an interface.(Inherited from Attribute.)


Retrieves the number of type information interfaces that an object provides (either 0 or 1).(Inherited from Attribute.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr)

Provides access to properties and methods exposed by an object.(Inherited from Attribute.)

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:

private void SetValuesOnSerializing(StreamingContext context)
    // Code not shown.

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.

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: ");

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

            formatter.Serialize(stream, obj);

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

            // Set the original variable to null.
            obj = null;

            // 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: ");
        catch (SerializationException se)
            Console.WriteLine("Failed to serialize. Reason: " + se.Message);
        catch (Exception exc)
            Console.WriteLine("An exception occurred. Reason: " + exc.Message);
            obj = null;
            formatter = null;


// This is the object that will be serialized and deserialized.
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.
    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);

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

    internal void OnSerializedMethod(StreamingContext context)
        member2 = "This value was reset after serialization.";

    internal void OnDeserializingMethod(StreamingContext context)
        member3 = "This value was set during deserialization";

    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.'

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Available since 3.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1

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

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