---
title: SKPhysicsContactDelegate
framework: spritekit
role: symbol
role_heading: Protocol
path: spritekit/skphysicscontactdelegate
---

# SKPhysicsContactDelegate

Methods your app can implement to respond when physics bodies come into contact.

## Declaration

```swift
protocol SKPhysicsContactDelegate : NSObjectProtocol
```

## Mentioned in

Getting Started with Physics Responding to Frame-Cycle Events

## Overview

Overview An object that implements the SKPhysicsContactDelegate protocol can respond when two physics bodies with overlapping contactTestBitMask values are in contact with each other in a physics world. To receive contact messages, you set the contactDelegate property of a SKPhysicsWorld object. The delegate is called when a contact starts or ends. important: The physics contact delegate methods are called during the physics simulation step. During that time, the physics world can’t be modified and the behavior of any changes to the physics bodies in the simulation is undefined. If you need to make such changes, set a flag inside didBegin(_:) or didEnd(_:) and make changes in response to that flag in the update(_:for:) method in a SKSceneDelegate. You can use the contact delegate to play a sound or execute game logic, such as increasing a player’s score, when a contact event occurs. The following code shows how to display a shockwave effect when two nodes with the name ball come into contact. The code only creates the effect when the collision impulse is above a specified threshold: Listing 1. Creating a shockwave effect when objects come into contact let shockWaveAction: SKAction = {     let growAndFadeAction = SKAction.group([SKAction.scale(to: 50, duration: 0.5),                                             SKAction.fadeOut(withDuration: 0.5)])          let sequence = SKAction.sequence([growAndFadeAction,                                       SKAction.removeFromParent()])          return sequence }()

func didBegin(_ contact: SKPhysicsContact) {     if contact.collisionImpulse > 5 &&         contact.bodyA.node?.name == "ball" &&         contact.bodyB.node?.name == "ball" {                  let shockwave = SKShapeNode(circleOfRadius: 1)

shockwave.position = contact.contactPoint         scene.addChild(shockwave)                  shockwave.run(shockWaveAction)     } }

## Topics

### Responding to Contact Events

- [didBegin(_:)](spritekit/skphysicscontactdelegate/didbegin(_:).md)
- [didEnd(_:)](spritekit/skphysicscontactdelegate/didend(_:).md)

## Relationships

### Inherits From

- [NSObjectProtocol](objectivec/nsobjectprotocol.md)

## See Also

### Physics Simulation

- [Getting Started with Physics](spritekit/getting-started-with-physics.md)
- [SKPhysicsWorld](spritekit/skphysicsworld.md)
- [SKPhysicsBody](spritekit/skphysicsbody.md)
- [SKPhysicsContact](spritekit/skphysicscontact.md)
- [SKFieldNode](spritekit/skfieldnode.md)