See Also: SKPhysicsContactDelegate Members
The following example reverses gravity when a SpriteKit.SKPhysicsBody named "Ball" encounters one of the bodies named either "TopWall" or "BottomWall":
C# Example
public override void DidBeginContact(SKPhysicsContact contact) { if(contact.BodyA.Node.Name == "Ball" || contact.BodyB.Node.Name == "Ball") { if(contact.BodyA.Node.Name == "BottomWall" || contact.BodyB.Node.Name == "BottomWall" || contact.BodyA.Node.Name == "TopWall" || contact.BodyB.Node.Name == "TopWall") { world.Gravity = new PointF(0, -world.Gravity.Y); } } }