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C# in a Nutshell by Peter Drayton, Ted Neward, Ben Albahari

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[NonSerialized]

Even types with large amounts of important nontransient data sometimes contain members that are not appropriate for serialization. Common examples of transient members are fields that hold resources, such as file or window handles, that would not make sense on another machine or at a later time. Other examples of transient members that do not deserve to be serialized are fields that were calculated and cached in the type, but can be recreated from other, nontransient members. Lastly, a type may sometimes need to contain a member that is not serializable, yet still support serialization of the rest of the type.

To instruct the runtime’s serialization engine to ignore a member when serializing a type, mark it with the [NonSerialized] attribute, as follows:

[Serializable]
public sealed class Person {
  public string Name;
  public DateTime DateOfBirth;  
  [NonSerialized] public int Age; // Can be calculated
  // Rest of class
}

When serializing an instance of Person, the runtime ignores the Age member and does not write it to the output stream. Similarly, when deserializing an instance of Person, the input stream does not contain data for the Age member, which is set to the bit pattern representing 0 (i.e. null for references, 0 for integrals, etc.). Consequently, when using an object instance of a type such as Person that has been deserialized, remember to watch out for null and zeroed members.

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