# activeSubsystemOrStub

> The active display subsystem, if any. If no display subsystem is active, this property value references a default, stub subsystem whose members return safe values.

## Definition

* **Type:** Property
* **Namespace:** [UnityEngine.XR](/engine/6000.5/script-reference/unityengine/xr.md)
* **Assembly:** UnityEngine.XRModule

```csharp
public static XRDisplaySubsystem activeSubsystemOrStub { get; }
```

### Remarks

This helper property references a stub display subsystem instead of `null` when no display subsystem is active. The property is intended for use when updating obsolete APIs in the `XRDevice` and `XRStats` classes to the replacement APIs in `XRDisplaySubsystem`. You should not use this property in your own code. Instead, use the [XRDisplaySubsystem.activeSubsystem](/engine/6000.5/script-reference/unityengine/xr/xrdisplaysubsystem/activesubsystem.md) property and check whether it is `null`. Explicitly checking for `null` allows you to correctly handle cases where an XR display is unavailable. In addition, the returned stub display subsystem only provides safe default values for those members needed to replace the deprecated APIs. Therefore, accessing other display subsystem members could produce unexpected results.