# NetworkBehaviour Callbacks

**See also <xref:Mirror.NetworkBehaviour> in the API Reference.**

There are a number of events relating to network behaviours that can occur over the course of a normal multiplayer game. These include events such as the host starting up, a player joining, or a player leaving. Each of these possible events has an associated callback that you can implement in your own code to take action when the event occurs.

When you create a script which inherits from `NetworkBehaviour`, you can write your own implementation of what should happen when these events occur. To do this, you override the virtual methods on the `NetworkBehaviour` class with your own implementation of what should happen when the given event occurs.

This is a full list of virtual methods (callbacks) that you can implement on `NetworkBehaviour`, and where they are called

## Server Only

- OnStartServer
    - called when behaviour is spawned on server
- OnStopServer
    - called when behaviour is destroyed or unspawned on server
- OnSerialize
    - called when behaviour is serialize before it is sent to client, when overriding make sure to call `base.OnSerialize`

## Client only

- OnStartClient
    - called when behaviour is spawned on client 
- OnStartAuthority
    - called when behaviour has authority when it is spawned (eg local player)
    - called when behaviour is given authority by the sever
- OnStartLocalPlayer
    - called when the behaviour is on the local player object

- OnStopAuthority
    - called when authority is taken from the object (eg local player is replaced but not destroyed)
- OnStopClient
    - called when object is destroyed on client by the `ObjectDestroyMessage` or `ObjectHideMessage` messages


# Example flows 

Below is some example call order for different modes

> NOTE: `Start` is called by unity before the first frame, while normally this happens after Mirror's callbacks. But if you dont call ` NetworkServer.Spawn` the same frame as `instantiate` then start may be called first

> Note: `OnRebuildObservers` and `OnSetHostVisibility` is now on `NetworkVisibility` instead of `NetworkBehaviour`

## Server mode

When a NetworkServer.Spawn is called (eg when new client connections and a player is created)
-   `OnStartServer`
-   `OnRebuildObservers`
-   `Start`

## Client mode

When local player is spawned for client
-   `OnStartAuthority`
-   `OnStartClient`
-   `OnStartLocalPlayer`
-   `Start`

## Host mode

These are only called on the **Player Game Objects** when a client connects:
-   `OnStartServer`
-   `OnRebuildObservers`
-   `OnStartAuthority`
-   `OnStartClient`
-   `OnSetHostVisibility`
-   `OnStartLocalPlayer`
-   `Start`