> ## Documentation Index
> Fetch the complete documentation index at: https://docs-unity.molca.id/llms.txt
> Use this file to discover all available pages before exploring further.
# MolcaInteractionBase
> Shared VR interaction behavior for XRI grab and analog controls.
**File:** `Assets/_MolcaSDK/_VR/Scripts/Base/MolcaInteractionBase.cs`
## When to use
Use this when building VR training content that needs Molca Interaction Base functionality.
## Role
* Discovers **`XRGrabInteractable`**
* Tracks **which interactor** is active
* **Lock / unlock** interaction
* Implements analog interaction contracts used by valve/knob flows
Concrete types: [Valve interaction](/vr/interactions/valve-interaction), [Knob interaction](/vr/interactions/knob-interaction), plus additional scripts under `Interactions/`.
## Code
Derive from **`MolcaInteractionBase`**, let **`Awake`** auto-pick **`XRBaseInteractable`** on the same object (or assign **`interactable`** in the Inspector), and implement **`UpdateInteraction()`** for per-frame behavior while the user is interacting. The base registers with **`ReferenceManager`** after **`RuntimeManager`** is ready.
```csharp theme={null}
using MolcaSDK.VR;
using UnityEngine;
public class CustomLeverInteraction : MolcaInteractionBase
{
protected override void UpdateInteraction()
{
// Per-frame while isInteracting — drive rotation, haptics, step completion, etc.
}
}
```
Compare with **`ValveInteraction`** / **`KnobInteraction`** for analog value plumbing.
## Troubleshooting
* **Interactable null** — Assign **`interactable`** or rely on **`Awake`** (same **`GameObject`** only — no child search).
* **Reference / SceneObjectReference not found** — **`ReferenceManager.Register`** runs after **`WaitForInitialization`**; ensure **`ReferenceManager`** exists and **`refId`** is stable (**`OnValidate`** generates ids).
* **Unexpected drops** — **`maxInteractionDistance`** > 0 forces **`ForceRelease`** when hand is too far; set **0** to disable.
* **`UpdateInteraction` not running** — Only called while **`isInteracting`**; verify XRI **`selectEntered`** / **`selectExited`** wiring on **`interactable`**.
## Related
* [Recipe: Implement custom VR interactions](/recipes/implement-custom-vr-interaction) — step-by-step guide for creating custom VR interaction components
## Unity Editor
