---
title: "collisionBehavior(_:beganContactFor:withBoundaryIdentifier:at:)"
framework: uikit
role: symbol
role_heading: Instance Method
path: "uikit/uicollisionbehaviordelegate/collisionbehavior(_:begancontactfor:withboundaryidentifier:at:)"
---

# collisionBehavior(_:beganContactFor:withBoundaryIdentifier:at:)

Called when a collision, between a dynamic item and a collision boundary, has begun.

## Declaration

```swift
optional func collisionBehavior(_ behavior: UICollisionBehavior, beganContactFor item: any UIDynamicItem, withBoundaryIdentifier identifier: (any NSCopying)?, at p: CGPoint)
```

## Parameters

- `behavior`: The collision behavior that owns the dynamic item that has started contact with a boundary.
- `item`: The dynamic item that has started contact with a boundary.
- `identifier`: The identifier of the boundary that the dynamic item has started contact with.
- `p`: The collision point on the boundary.

## See Also

### Responding to UIKit Dynamics collisions

- [collisionBehavior(_:beganContactFor:with:at:)](uikit/uicollisionbehaviordelegate/collisionbehavior(_:begancontactfor:with:at:).md)
- [collisionBehavior(_:endedContactFor:withBoundaryIdentifier:)](uikit/uicollisionbehaviordelegate/collisionbehavior(_:endedcontactfor:withboundaryidentifier:).md)
- [collisionBehavior(_:endedContactFor:with:)](uikit/uicollisionbehaviordelegate/collisionbehavior(_:endedcontactfor:with:).md)