C# in a Nutshell, Second Edition

[Serializable]

In the preceding examples we assumed for simplicity’s sake that the object graph was serializable, and we focused on how serialization and deserialization occurred. Now let’s spend some time defining what it means for an object or object graph to be serializable, and how to mark your classes and structs as such.

Types that should support being serialized and deserialized by the runtime must be marked with the [Serializable] attribute, as follows:

[Serializable]
public sealed class Person {
  public string Name;
  public int Age;
}

This sets a special serializable bit in the metadata for the type that instructs the runtime to provide serialization and deserialization support. The [Serializable] attribute is not inherited, thus derived types are not automatically serializable. To provide for the serialization of derived types, mark each type as [Serializable].

As we saw earlier in the section “Implicit Serialization,” serializing a type implicitly serializes all members of the type, recursively. This implies that all members of a type must themselves be serializable for the type to successfully serialize. This is true regardless of the accessibility of the members. For example, if you modify the Person class as follows, it will no longer be serializable:

[Serializable]
public sealed class Person {
  public string Name;
  public int Age;
  private Company Employer; // Person no longer Serializable!
}
  
public class Company {...}

Attempting to serialize an instance of Person now results ...