# SyncVars

SyncVars are properties of classes that inherit from NetworkBehaviour, which are synchronized from the server to clients. When a game object is spawned, or a new player joins a game in progress, they are sent the latest state of all SyncVars on networked objects that are visible to them. Use the `SyncVar` custom attribute to specify which variables in your script you want to synchronize.

The state of SyncVars is applied to game objects on clients before `OnStartClient()` is called, so the state of the object is always up-to-date inside `OnStartClient()`.

SyncVars can use any [type supported by Mirror](https://mirror-networking.gitbook.io/docs/manual/guides/data-types). You can have up to 64 SyncVars on a single NetworkBehaviour script, including SyncLists (see next section, below).

The server automatically sends SyncVar updates when the value of a SyncVar changes, so you do not need to track when they change or send information about the changes yourself. Changing a value in the inspector will not trigger an update.

> The [SyncVar hook](https://mirror-networking.gitbook.io/docs/manual/guides/synchronization/syncvar-hooks) attribute can be used to specify a method to be called when the SyncVar changes value on the client.

## SyncVar Example <a href="#syncvar-example" id="syncvar-example"></a>

Let's say we have a networked object with a script called Enemy:

```csharp
public class Enemy : NetworkBehaviour
{
    [SyncVar]
    public int health = 100;

    void OnMouseUp()
    {
        if (NetworkClient.localPlayer.TryGetComponent(out PlayerController pc))
            pc.currentTarget = gameObject;
    }
}
```

The `PlayerController` might look like this:

```csharp
public class PlayerController : NetworkBehaviour
{
    public GameObject currentTarget;

    void Update()
    {
        if (isLocalPlayer)
            if (currentTarget != null && currentTarget.tag == "Enemy")
                if (Input.GetKeyDown(KeyCode.X))
                    CmdShoot(currentTarget);
    }

    [Command]
    public void CmdShoot(GameObject enemy)
    {
        // Do your own shot validation here because this runs on the server
        enemy.GetComponent<Enemy>().health -= 5;
    }
}
```

In this example, when a Player clicks on an Enemy, the networked enemy game object is assigned to `PlayerController.currentTarget`. When the player presses X, with a correct target selected, that target is passed through a Command, which runs on the server, to decrement the `health` SyncVar. All clients will be updated with that new value. You can then have a UI on the enemy to show the current value.

## Class inheritance <a href="#class-inheritance" id="class-inheritance"></a>

SyncVars work with class inheritance. Consider this example:

```csharp
class Pet : NetworkBehaviour
{
    [SyncVar] 
    string name;
}

class Cat : Pet
{
    [SyncVar]
    public Color32 color;
}
```

You can attach the Cat component to your cat prefab, and it will synchronize both it's `name` and `color`.

> **Warning** Both `Cat` and `Pet` should be in the same assembly. If they are in separate assemblies, make sure not to change `name` from inside `Cat` directly, add a method to `Pet` instead.