The hook attribute can be used to specify a function to be called when the SyncVar changes value on the client.
- The Hook method must have two parameters of the same type as the SyncVar property. One for the old value, one for the new value.
- The Hook is always called after the property value is set. You don't need to set it yourself.
- The Hook only fires for changed values, and changing a value in the inspector will not trigger an update.
- As of version 11.1.4 (March 2020) and later, hooks can be virtual methods and overriden in a derived class.
Below is a simple example of assigning a random color to each player when they're spawned on the server. All clients will see all players in the correct colors, even if they join later.
Note: The signature for hook methods was changed in version 9.0 (Feb 2020) to having 2 parameters (old and new values). If you're on an older version, hook methods just have one parameter (new value).
public class PlayerController : NetworkBehaviour
[SyncVar(hook = nameof(SetColor))]
Color playerColor = Color.black;
// Unity makes a clone of the Material every time GetComponent().material is used.
// Cache it here and Destroy it in OnDestroy to prevent a memory leak.
public override void OnStartServer()
playerColor = Random.ColorHSV(0f, 1f, 1f, 1f, 0.5f, 1f);
void SetColor(Color oldColor, Color newColor)
if (cachedMaterial == null)
cachedMaterial = GetComponent().material;
cachedMaterial.color = newColor;
Hooks are invoked in the order the syncvars are defined in the file.
public class MyBehaviour : NetworkBehaviour
[SyncVar(hook = nameof(Hook1))]
[SyncVar(hook = nameof(Hook2))]
if X, Y, and Z are all set on the server at the same time then the call order will be:
- 1.X value is set
- 2.Y value is set
- 3.Hook1 is called
- 4.Z value is set
- 5.Hook2 is called