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Provide deserialization methods for optional fields

TypeName

ProvideDeserializationMethodsForOptionalFields

CheckId

CA2239

Category

Microsoft.Usage

Breaking Change

Non Breaking

A type has a field that is marked with the System.Runtime.Serialization.OptionalFieldAttribute attribute and the type does not provide de-serialization event handling methods.

The OptionalFieldAttribute attribute has no effect on serialization; a field marked with the attribute is serialized. However, the field is ignored on de-serialization and retains the default value associated with its type. De-serialization event handlers should be declared to set the field during the de-serialization process.

To fix a violation of this rule, add de-serialization event handling methods to the type.

It is safe to suppress a warning from this rule if the field should be ignored during the de-serialization process.

The following example shows a type with an optional field and de-serialization event handling methods.

using System;
using System.Reflection;
using System.Runtime.Serialization;

[assembly: AssemblyVersionAttribute("2.0.0.0")]
namespace UsageLibrary
{
   [SerializableAttribute]
   public class SerializationEventHandlers
   {
      [OptionalFieldAttribute(VersionAdded = 2)]
      int optionalField = 5;

      [OnDeserializingAttribute]
      void OnDeserializing(StreamingContext context)
      {
         optionalField = 5;
      }

      [OnDeserializedAttribute]
      void OnDeserialized(StreamingContext context)
      {
         // Set optionalField if dependent on other deserialized values.
      }
   }
}

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