Writing a custom state serializer

While initially a game might simply serialize Transform or Rigidbody for testing, eventually it is often necessary to write a custom serialization function. This is a surprisingly easy task.

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Here is a script that sends an object's position over the network:

using UnityEngine;
using System.Collections;

public class ExampleUnityNetworkSerializePosition : MonoBehaviour
{
  public void OnSerializeNetworkView( BitStream stream, NetworkMessageInfo info )
  {
    // we are currently writing information to the network
    if( stream.isWriting )
    {
      // send the object's position
      Vector3 position = transform.position;
      stream.Serialize( ref position );
    }
    // we are currently reading information from the network
    else
    {
      // read the first vector3 and store it in 'position'
      Vector3 position = Vector3.zero;
      stream.Serialize( ref position );
    
      // set the object's position to the value we were sent
      transform.position = position;
    }
  }
}

Most of the work is done with BitStream. This is used to check if NetworkView is currently writing the state, or if it is reading the state from the network. Depending on whether it is reading or writing, stream.Serialize behaves differently. If NetworkView is writing, the value will be sent over the network. However, if NetworkView is reading, the value will be read from the network and saved in the referenced variable (thus the ref keyword, which passes Vector3 by reference rather than value).