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ISerializable Interface

Allows an object to control its own serialization and deserialization.

For a list of all members of this type, see ISerializable Members.

[Visual Basic]
Public Interface ISerializable
[C#]
public interface ISerializable
[C++]
public __gc __interface ISerializable
[JScript]
public interface ISerializable

Classes that Implement ISerializable

Class Description
Assembly Defines an Assembly, which is a reusable, versionable, and self-describing building block of a common language runtime application.
AssemblyName Describes an assembly's unique identity in full.
AxHost.State Encapsulates the persisted state of an ActiveX control.
Cursor Represents the image used to paint the mouse pointer.
DataSet Represents an in-memory cache of data.
DataTable Represents one table of in-memory data.
DBNull Represents a null value.
Delegate Represents a delegate, which is a data structure that refers to a static method or to a class instance and an instance method of that class.
EventLogEntry Encapsulates a single record in the event log. This class cannot be inherited.
Exception Represents errors that occur during application execution.
FileSystemInfo Provides the base class for both FileInfo and DirectoryInfo objects.
Font Defines a particular format for text, including font face, size, and style attributes. This class cannot be inherited.
Hash Provides evidence about the hash value for an assembly. This class cannot be inherited.
Hashtable Represents a collection of key-and-value pairs that are organized based on the hash code of the key.
Icon Represents a Windows icon, which is a small bitmap image used to represent an object. Icons can be thought of as transparent bitmaps, although their size is determined by the system.
Image An abstract base class that provides functionality for the Bitmap and Metafile descended classes.
ImageListStreamer Provides the data portion of an ImageList.
ListViewItem Represents an item in a ListView control.
LogicalCallContext Provides a set of properties that are carried with the execution code path during remote method calls.
ManagementBaseObject Contains the basic elements of a management object. It serves as a base class to more specific management object classes.
Module Performs reflection on a module.
NameObjectCollectionBase Provides the abstract (MustInherit in Visual Basic) base class for a collection of associated String keys and Object values that can be accessed either with the key or with the index.
ObjRef Stores all relevant information required to generate a proxy in order to communicate with a remote object.
Pointer Provides a wrapper class for pointers.
Regex Represents an immutable regular expression.
SoapFault Carries error and status information within a SOAP message. This class cannot be inherited.
ToolboxItem Provides a base implementation of a toolbox item.
TreeNode Represents a node of a TreeView.
Uri Provides an object representation of a uniform resource identifier (URI) and easy access to the parts of the URI.
WeakReference Represents a weak reference, which references an object while still allowing it to be garbage collected.
WebProxy Contains HTTP proxy settings for the WebRequest class.
WebRequest Makes a request to a Uniform Resource Identifier (URI). This is an abstract (MustInherit in Visual Basic) class.
WebResponse Provides a response from a Uniform Resource Identifier (URI). This is an abstract (MustInherit in Visual Basic) class.
WindowsIdentity Represents a Windows user.

Remarks

Any class that might be serialized must be marked with the SerializableAttribute. If a class needs to control its serialization process, it can implement the ISerializable interface. The Formatter calls the GetObjectData at serialization time and populates the supplied SerializationInfo with all the data required to represent the object. The Formatter creates a SerializationInfo with the type of the object in the graph. Objects that need to send proxies for themselves can use the FullTypeName and AssemblyName methods on SerializationInfo to change the transmitted information.

If a parent class of the serialized class implements ISerializable, call the implementation of GetObjectData for your base class.

The ISerializable interface implies a constructor with the signature Constructor(SerializationInfo info, StreamingContext context). At deserialization time, the current constructor is called only after the data in the SerializationInfo has been deserialized by the formatter. In general this constructor should be protected if the class is not sealed (NotInheritable in Visual Basic) .

The serialization architecture handles object types that extend MarshalByRefObject the same as types that extend Object. These types can be marked with the SerializableAttribute and implement the ISerializable interface as any other object type. Their object state will be captured and persisted onto the stream.

When these types are being used through System.Runtime.Remoting, the remoting infrastructure provides a surrogate that preempts normal serialization and instead serializes a proxy to the MarshalByRefObject. A surrogate is a helper that knows how to serialize and deserialize objects of a particular type. The proxy, invisible to the user in most cases, will be of type ObjRef.

CAUTION   As a general design pattern, it would be unusual for a class to be both marked with the serializable attribute and extend MarshalByRefObject. Developers should think carefully about the possible serialization and remoting scenarios when combining these two characteristics. One example where this might be applicable is with a MemoryStream. While the base class of MemoryStream (Stream) extends from MarshalByRefObject, it is possible to capture the state of a MemoryStream and restore it at will. It might, therefore, be meaningful to serialize the state of this stream into a database and restore it at some later point in time. However, when used through remoting, an object of this type would be proxied.

For more details about serialization of classes that extend MarshalByRefObject see RemotingSurrogateSelector. For more information about implementing ISerializable, see Custom Serialization.

Notes to Implementers:  Implement this interface to allow an object to take part in its own serialization and deserialization.

Example

[Visual Basic, C#, C++] The following code example demonstrates the use of the ISerializable interface to define custom serialization behavior for a class.

[Visual Basic] 
Imports System
Imports System.IO
Imports System.Collections
Imports System.Runtime.Serialization.Formatters.Binary
Imports System.Runtime.Serialization


' There should be only one instance of this type per AppDomain.
<Serializable()> Public NotInheritable Class Singleton
   Implements ISerializable

   ' This is the one instance of this type.
   Private Shared ReadOnly theOneObject As New Singleton

   ' Here are the instance fields.
   Public someString As String
   Public someNumber As Int32

   ' Private constructor allowing this type to construct the Singleton.
   Private Sub New()
      ' Do whatever is necessary to initialize the Singleton.
      someString = "This is a string field"
      someNumber = 123
   End Sub

   ' A method returning a reference to the Singleton.
   Public Shared Function GetSingleton() As Singleton
      Return theOneObject
   End Function

   ' A method called when serializing a Singleton.
   Private Sub GetObjectData(ByVal info As SerializationInfo, _
      ByVal context As StreamingContext) _
      Implements ISerializable.GetObjectData

      ' Instead of serializing this object, we will  
      ' serialize a SingletonSerializationHelp instead.
      info.SetType(GetType(SingletonSerializationHelper))
      ' No other values need to be added.
   End Sub

   ' Note: ISerializable's special constructor is not necessary 
   ' because it is never called.
End Class


<Serializable()> Friend NotInheritable Class SingletonSerializationHelper
   Implements IObjectReference
   ' This object has no fields (although it could).

   ' GetRealObject is called after this object is deserialized.
   Public Function GetRealObject(ByVal context As StreamingContext) As Object Implements IObjectReference.GetRealObject
      ' When deserialiing this object, return a reference to 
      ' the Singleton object instead.
      Return Singleton.GetSingleton()
   End Function
End Class


Class App
   <STAThread()> Shared Sub Main()
      Dim fs As New FileStream("DataFile.dat", FileMode.Create)

      Try
         ' Construct a BinaryFormatter and use it 
         ' to serialize the data to the stream.
         Dim formatter As New BinaryFormatter

         ' Create an array with multiple elements refering to 
         ' the one Singleton object.
         Dim a1() As Singleton = {Singleton.GetSingleton(), Singleton.GetSingleton()}

         ' This displays "True".
         Console.WriteLine("Do both array elements refer to the same object? " & _
            Object.ReferenceEquals(a1(0), a1(1)))

         ' Serialize the array elements.
         formatter.Serialize(fs, a1)

         ' Deserialize the array elements.
         fs.Position = 0
         Dim a2() As Singleton = DirectCast(formatter.Deserialize(fs), Singleton())

         ' This displays "True".
         Console.WriteLine("Do both array elements refer to the same object? " & _
            Object.ReferenceEquals(a2(0), a2(1)))

         ' This displays "True".
         Console.WriteLine("Do all array elements refer to the same object? " & _
            Object.ReferenceEquals(a1(0), a2(0)))
      Catch e As SerializationException
         Console.WriteLine("Failed to serialize. Reason: " & e.Message)
         Throw
      Finally
         fs.Close()
      End Try
   End Sub
End Class

[C#] 
using System;
using System.IO;
using System.Collections;
using System.Runtime.Serialization.Formatters.Binary;
using System.Runtime.Serialization;


// There should be only one instance of this type per AppDomain.
[Serializable]
public sealed class Singleton : ISerializable 
{
    // This is the one instance of this type.
    private static readonly Singleton theOneObject = new Singleton();

    // Here are the instance fields.
    public String someString;
    public Int32 someNumber;

    // Private constructor allowing this type to construct the Singleton.
    private Singleton() 
    { 
        // Do whatever is necessary to initialize the Singleton.
        someString = "This is a string field";
        someNumber = 123;
    }

    // A method returning a reference to the Singleton.
    public static Singleton GetSingleton() 
    { 
        return theOneObject; 
    }

    // A method called when serializing a Singleton.
    void ISerializable.GetObjectData(
        SerializationInfo info, StreamingContext context) 
    {
        // Instead of serializing this object, 
        // serialize a SingletonSerializationHelp instead.
        info.SetType(typeof(SingletonSerializationHelper));
        // No other values need to be added.
    }

    // Note: ISerializable's special constructor is not necessary 
    // because it is never called.
}


[Serializable]
internal sealed class SingletonSerializationHelper : IObjectReference 
{
    // This object has no fields (although it could).

    // GetRealObject is called after this object is deserialized.
    public Object GetRealObject(StreamingContext context) 
    {
        // When deserialiing this object, return a reference to 
        // the Singleton object instead.
        return Singleton.GetSingleton();
    }
}


class App 
{
    [STAThread]
    static void Main() 
    {
        FileStream fs = new FileStream("DataFile.dat", FileMode.Create);

        try 
        {
            // Construct a BinaryFormatter and use it 
            // to serialize the data to the stream.
            BinaryFormatter formatter = new BinaryFormatter();

            // Create an array with multiple elements refering to 
            // the one Singleton object.
            Singleton[] a1 = { Singleton.GetSingleton(), Singleton.GetSingleton() };

            // This displays "True".
            Console.WriteLine(
                "Do both array elements refer to the same object? " + 
                (a1[0] == a1[1]));     

            // Serialize the array elements.
            formatter.Serialize(fs, a1);

            // Deserialize the array elements.
            fs.Position = 0;
            Singleton[] a2 = (Singleton[]) formatter.Deserialize(fs);

            // This displays "True".
            Console.WriteLine("Do both array elements refer to the same object? " 
                + (a2[0] == a2[1])); 

            // This displays "True".
            Console.WriteLine("Do all array elements refer to the same object? " 
                + (a1[0] == a2[0]));
        }   
        catch (SerializationException e) 
        {
            Console.WriteLine("Failed to serialize. Reason: " + e.Message);
            throw;
        }
        finally 
        {
            fs.Close();
        }
    }
}

[C++] 
#using <mscorlib.dll>

using namespace System;
using namespace System::IO;
using namespace System::Collections;
using namespace System::Runtime::Serialization::Formatters::Binary;
using namespace System::Runtime::Serialization;


private __sealed __gc class SingletonSerializationHelper;

// There should be only one instance of this type per AppDomain.
[Serializable]
public __sealed __gc class Singleton : public ISerializable 
{
    // This is the one instance of this type.
private:
    static Singleton* theOneObject = new Singleton();

    // Here are the instance fields.
public:
    String* someString;
    Int32 someNumber;

    // Private constructor allowing this type to construct the singleton.
private:
    Singleton() 
    { 
        // Do whatever is necessary to initialize the singleton.
        someString = S"This is a String* field";
        someNumber = 123;
    }

    // A method returning a reference to the singleton.
public:
    static Singleton* GetSingleton() 
    { 
        return theOneObject; 
    }

    // A method called when serializing a Singleton.
    void GetObjectData(SerializationInfo* info, StreamingContext context) 
    {
        // Instead of serializing this Object*, we will  
        // serialize a SingletonSerializationHelp instead.
        info->SetType(__typeof(SingletonSerializationHelper));
        // No other values need to be added.
    }

    // NOTE: ISerializable*'s special constructor is NOT necessary 
    // because it's never called
};

[Serializable]
    private __sealed __gc class SingletonSerializationHelper : public IObjectReference 
    {
        // This Object* has no fields (although it could).
        // GetRealObject is called after this Object* is deserialized
    public:
        Object* GetRealObject(StreamingContext context) 
        {
            // When deserialiing this Object*, return a reference to 
            // the singleton Object* instead.
            return Singleton::GetSingleton();
        }
    };

[STAThread]
int main() 
{
    FileStream* fs = new FileStream(S"DataFile.dat", FileMode::Create);

    try 
    {
        // Construct a BinaryFormatter and use it 
        // to serialize the data to the stream.
        BinaryFormatter* formatter = new BinaryFormatter();

        // Create an array with multiple elements refering to 
        // the one Singleton Object*.
        Singleton* a1[] = { Singleton::GetSingleton(), Singleton::GetSingleton() };

        // This displays S"True".
        Console::WriteLine(S"Do both array elements refer to the same Object? {0}", __box((a1->Item[0] == a1->Item[1])));

        // Serialize the array elements.
        formatter->Serialize(fs, a1);

        // Deserialize the array elements.
        fs->Position = 0;
        Singleton* a2[] = (Singleton* __gc[]) formatter->Deserialize(fs);

        // This displays S"True".
        Console::WriteLine(S"Do both array elements refer to the same Object? {0}", __box((a2->Item[0] == a2->Item[1]))); 

        // This displays S"True".
        Console::WriteLine(S"Do all  array elements refer to the same Object? {0}", __box((a1->Item[0] == a2->Item[0])));
    } 
    catch (SerializationException* e) 
    {
        Console::WriteLine(S"Failed to serialize. Reason: {0}", e->Message);
        throw;
    }
    __finally 
    {
        fs->Close();
    }
    return 0;
}

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Namespace: System.Runtime.Serialization

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

Assembly: Mscorlib (in Mscorlib.dll)

See Also

ISerializable Members | System.Runtime.Serialization Namespace | XML and SOAP Serialization | RemotingSurrogateSelector | Custom Serialization

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