# PhysicsShape.ContactId

> The unique Id of the contact. This contact is volatile and may be destroyed automatically when the world is modified or simulated therefore it should always be checked for validity.

## Definition

* **Type:** Struct
* **Namespace:** [Unity.U2D.Physics](/engine/6000.6/script-reference/unity/u2d/physics.md)
* **Assembly:** UnityEngine.PhysicsCore2DModule

```csharp
public readonly struct PhysicsShape.ContactId
```

## Properties

| Property                                                                                       | Description                           |
| ---------------------------------------------------------------------------------------------- | ------------------------------------- |
| [contact](/engine/6000.6/script-reference/unity/u2d/physics/physicsshape/contactid/contact.md) | Get the contact.                      |
| [isValid](/engine/6000.6/script-reference/unity/u2d/physics/physicsshape/contactid/isvalid.md) | Check if the contact is valid or not. |