CA2240: Implement ISerializable correctly

TypeName	ImplementISerializableCorrectly
CheckId	CA2240
Category	Microsoft.Usage
Breaking Change	Non Breaking

Cause

An externally visible type is assignable to the System.Runtime.Serialization.ISerializable interface and one of the following conditions is true:

• The type inherits but does not override the ISerializable.GetObjectData method and the type declares instance fields that are not marked with the System.NonSerializedAttribute attribute.

• The type is not sealed and the type implements a GetObjectData method that is not externally visible and overridable.

Rule Description

Instance fields that are declared in a type that inherits the System.Runtime.Serialization.ISerializable interface are not automatically included in the serialization process. To include the fields, the type must implement the GetObjectData method and the serialization constructor. If the fields should not be serialized, apply the NonSerializedAttribute attribute to the fields to explicitly indicate the decision.

In types that are not sealed, implementations of the GetObjectData method should be externally visible. Therefore, the method can be called by derived types, and is overridable.

How to Fix Violations

To fix a violation of this rule, make the GetObjectData method visible and overridable and make sure all instance fields are included in the serialization process or explicitly marked with the NonSerializedAttribute attribute.

When to Suppress Warnings

Do not suppress a warning from this rule.

Example

The following example shows two serializable types that violate the rule.

Imports System
Imports System.Security.Permissions
Imports System.Runtime.Serialization

Namespace Samples1

    ' Violates this rule
    <Serializable()> _
    Public Class Book
        Implements ISerializable

        Private ReadOnly _Title As String

        Public Sub New(ByVal title As String)
            If (title Is Nothing) Then Throw New ArgumentNullException("title")
            _Title = title
        End Sub

        Protected Sub New(ByVal info As SerializationInfo, ByVal context As StreamingContext)
            If (info Is Nothing) Then Throw New ArgumentNullException("info")

            _Title = info.GetString("Title")
        End Sub

        Public ReadOnly Property Title() As String
            Get
                Return _Title
            End Get
        End Property

        <SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags:=SecurityPermissionFlag.SerializationFormatter)> _
        Public Sub GetObjectData(ByVal info As SerializationInfo, ByVal context As StreamingContext) _
            Implements ISerializable.GetObjectData

            If (info Is Nothing) Then Throw New ArgumentNullException("info")

            info.AddValue("Title", _Title)
        End Sub
    End Class

    ' Violates this rule
    <Serializable()> _
    Public Class LibraryBook
        Inherits Book

        Private ReadOnly _CheckedOut As Date

        Public Sub New(ByVal text As String, ByVal checkedOut As Date)
            MyBase.New(text)
            _CheckedOut = checkedOut
        End Sub

        Public ReadOnly Property CheckedOut() As Date
            Get
                Return _CheckedOut
            End Get
        End Property

    End Class
End Namespace

using System;
using System.Security.Permissions;
using System.Runtime.Serialization;

namespace Samples1
{
    // Violates this rule
    [Serializable]
    public class Book : ISerializable
    {
        private readonly string _Text;

        public Book(string text)
        {
            if (text == null)
                throw new ArgumentNullException("text");

            _Text = text;
        }

        protected Book(SerializationInfo info, StreamingContext context)
        {
            if (info == null)
                throw new ArgumentNullException("info");

            _Text = info.GetString("Text");
        }

        public string Text
        {
            get { return _Text; }
        }

        [SecurityPermission(SecurityAction.Demand, SerializationFormatter = true)]
        public void GetObjectData(SerializationInfo info, StreamingContext context)
        {
            if (info == null)
                throw new ArgumentNullException("info");

            info.AddValue("Text", _Text);
        }
    }

    // Violates this rule
    [Serializable]
    public class LibraryBook : Book
    {
        private readonly DateTime _CheckedOut;

        public LibraryBook(string text, DateTime checkedOut)
            : base(text)
        {
            _CheckedOut = checkedOut;
        }

        public DateTime CheckedOut
        {
            get { return _CheckedOut; }
        }
    }
}

using namespace System;
using namespace System::Security::Permissions;
using namespace System::Runtime::Serialization;

namespace Samples1 
{
    // Violates this rule
    [Serializable]
    public ref class Book : ISerializable
    {
    private:
        initonly String^ _Title;

    public: 
        Book(String^ title)
        {
            if (title == nullptr)
                throw gcnew ArgumentNullException("title");

            _Title = title;
        }

        property String^ Title
        {
            String^ get()
            {
                return _Title;
            }
        }

    protected: 
        Book(SerializationInfo^ info, StreamingContext context)
        {
            if (info == nullptr)
                throw gcnew ArgumentNullException("info");

            _Title = info->GetString("Title");
        }

    private:
        [SecurityPermission(SecurityAction::LinkDemand, Flags = SecurityPermissionFlag::SerializationFormatter)]
        void virtual GetObjectData(SerializationInfo^ info, StreamingContext context) sealed = ISerializable::GetObjectData
        {
            if (info == nullptr)
                throw gcnew ArgumentNullException("info");

            info->AddValue("Title", _Title);
        }
    };

    // Violates this rule
    [Serializable]
    public ref class LibraryBook : Book
    {
        initonly DateTime _CheckedOut;

    public:
        LibraryBook(String^ title, DateTime checkedOut) : Book(title)
        {
            _CheckedOut = checkedOut;
        }

        property DateTime CheckedOut
        {
            DateTime get()
            {
                return _CheckedOut;
            }
        }
    };
}

The following example fixes the two previous violations by providing an overrideable implementation of [ISerializable.GetObjectData] on the Book class and by providing an implementation of [ISerializable.GetObjectData] on the Library class.

Imports System
Imports System.Security.Permissions
Imports System.Runtime.Serialization

Namespace Samples2

    <Serializable()> _
    Public Class Book
        Implements ISerializable

        Private ReadOnly _Title As String

        Public Sub New(ByVal title As String)
            If (title Is Nothing) Then Throw New ArgumentNullException("title")
            _Title = title
        End Sub

        Protected Sub New(ByVal info As SerializationInfo, ByVal context As StreamingContext)
            If (info Is Nothing) Then Throw New ArgumentNullException("info")

            _Title = info.GetString("Title")
        End Sub

        Public ReadOnly Property Title() As String
            Get
                Return _Title
            End Get
        End Property

        <SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags:=SecurityPermissionFlag.SerializationFormatter)> _
        Protected Overridable Sub GetObjectData(ByVal info As SerializationInfo, ByVal context As StreamingContext) _
            Implements ISerializable.GetObjectData

            If (info Is Nothing) Then Throw New ArgumentNullException("info")

            info.AddValue("Title", _Title)
        End Sub
    End Class


    <Serializable()> _
    Public Class LibraryBook
        Inherits Book

        Private ReadOnly _CheckedOut As Date

        Public Sub New(ByVal text As String, ByVal checkedOut As Date)
            MyBase.New(text)
            _CheckedOut = checkedOut
        End Sub

        Protected Sub New(ByVal info As SerializationInfo, ByVal context As StreamingContext)
            MyBase.New(info, context)

            _CheckedOut = info.GetDateTime("CheckedOut")
        End Sub

        Public ReadOnly Property CheckedOut() As Date
            Get
                Return _CheckedOut
            End Get
        End Property

        <SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags:=SecurityPermissionFlag.SerializationFormatter)> _
        Protected Overrides Sub GetObjectData(ByVal info As System.Runtime.Serialization.SerializationInfo, _
                                              ByVal context As System.Runtime.Serialization.StreamingContext)

            MyBase.GetObjectData(info, context)

            info.AddValue("CheckedOut", _CheckedOut)
        End Sub
    End Class
End Namespace

using System;
using System.Security.Permissions;
using System.Runtime.Serialization;

namespace Samples2
{
    [Serializable]
    public class Book : ISerializable
    {
        private readonly string _Title;

        public Book(string title)
        {
            if (title == null)
                throw new ArgumentNullException("title");

            _Title = title;
        }

        protected Book(SerializationInfo info, StreamingContext context)
        {
            if (info == null)
                throw new ArgumentNullException("info");

            _Title = info.GetString("Title");
        }

        public string Title
        {
            get { return _Title; }
        }

        [SecurityPermission(SecurityAction.Demand, SerializationFormatter = true)]
        protected virtual void GetObjectData(SerializationInfo info, StreamingContext context)
        {
            info.AddValue("Title", _Title);
        }

        [SecurityPermission(SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.SerializationFormatter)]
        void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
        {
            if (info == null)
                throw new ArgumentNullException("info");

            GetObjectData(info, context);
        }
    }

    [Serializable]
    public class LibraryBook : Book
    {
        private readonly DateTime _CheckedOut;

        public LibraryBook(string title, DateTime checkedOut)
            : base(title)
        {
            _CheckedOut = checkedOut;
        }

        protected LibraryBook(SerializationInfo info, StreamingContext context)
            : base(info, context)
        {
            _CheckedOut = info.GetDateTime("CheckedOut");
        }

        public DateTime CheckedOut
        {
            get { return _CheckedOut; }
        }

        [SecurityPermission(SecurityAction.Demand, SerializationFormatter = true)]
        protected override void GetObjectData(SerializationInfo info, StreamingContext context)
        {
            base.GetObjectData(info, context);

            info.AddValue("CheckedOut", _CheckedOut);
        }
    }
}

using namespace System;
using namespace System::Security::Permissions;
using namespace System::Runtime::Serialization;

namespace Samples2 
{
    [Serializable]
    public ref class Book : ISerializable
    {
    private:
        initonly String^ _Title;

    public: 
        Book(String^ title)
        {
            if (title == nullptr)
                throw gcnew ArgumentNullException("title");

            _Title = title;
        }

        property String^ Title
        {
            String^ get()
            {
                return _Title;
            }
        }

    protected: 
        Book(SerializationInfo^ info, StreamingContext context)
        {
            if (info == nullptr)
                throw gcnew ArgumentNullException("info");

            _Title = info->GetString("Title");
        }

        [SecurityPermission(SecurityAction::LinkDemand, Flags = SecurityPermissionFlag::SerializationFormatter)]
        void virtual GetObjectData(SerializationInfo^ info, StreamingContext context) = ISerializable::GetObjectData
        {
            if (info == nullptr)
                throw gcnew ArgumentNullException("info");

            info->AddValue("Title", _Title);
        }
    };

    [Serializable]
    public ref class LibraryBook : Book
    {
        initonly DateTime _CheckedOut;

    public:
        LibraryBook(String^ title, DateTime checkedOut) 
            : Book(title)
        {
            _CheckedOut = checkedOut;
        }

        property DateTime CheckedOut
        {
            DateTime get()
            {
                return _CheckedOut;
            }
        }

    protected: 
        LibraryBook(SerializationInfo^ info, StreamingContext context) : Book(info, context)
        {
            _CheckedOut = info->GetDateTime("CheckedOut");
        }

        [SecurityPermission(SecurityAction::LinkDemand, Flags = SecurityPermissionFlag::SerializationFormatter)]
        void virtual GetObjectData(SerializationInfo^ info, StreamingContext context) override
        {
            Book::GetObjectData(info, context);
            info->AddValue("CheckedOut", _CheckedOut);
        }
    };
}

Related Rules

CA2236: Call base class methods on ISerializable types

CA2229: Implement serialization constructors

CA2238: Implement serialization methods correctly

CA2235: Mark all non-serializable fields

CA2237: Mark ISerializable types with SerializableAttribute

CA2239: Provide deserialization methods for optional fields

CA2120: Secure serialization constructors