Sprites not contacting properly - ios

Question

There's a ball and a paddle, the ball should be on the paddle and touching it but the ball never touches the paddle and stops before reaching the paddle, can anyone help me out?
import SpriteKit
class GameScene: SKScene ,SKPhysicsContactDelegate {
let ballCategory:UInt32 = 0x1 << 0
let bottomCategory:UInt32 = 0x1 << 1
let paddleCategory:UInt32 = 0x1 << 2
override init(size: CGSize){
super.init(size: size)
physicsWorld.contactDelegate = self
let ball = SKSpriteNode(imageNamed: "ball")
ball.position = CGPointMake(CGRectGetMidX(self.frame), CGRectGetMidY(self.frame))
addChild(ball)
ball.physicsBody = SKPhysicsBody(circleOfRadius: self.frame.size.width / 2)
ball.physicsBody?.dynamic = true
ball.physicsBody?.allowsRotation = false
ball.physicsBody?.friction = 0
// ball.physicsBody?.applyImpulse(CGVectorMake(2,-2))
ball.physicsBody?.categoryBitMask = ballCategory
ball.physicsBody?.contactTestBitMask = paddleCategory
ball.physicsBody?.collisionBitMask = paddleCategory
ball.physicsBody?.affectedByGravity = true
let paddle = SKSpriteNode(imageNamed: "paddle")
paddle.position = CGPointMake(CGRectGetMidX(self.frame), paddle.frame.size.height * 2)
addChild(paddle)
paddle.physicsBody = SKPhysicsBody(rectangleOfSize: paddle.frame.size)
paddle.physicsBody?.affectedByGravity = false
paddle.physicsBody?.dynamic = false
paddle.physicsBody?.categoryBitMask = paddleCategory
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
}
func didBeginContact(contact: SKPhysicsContact) {
print("touched")
}
override func update(currentTime: CFTimeInterval) {
/* Called before each frame is rendered */
}
}

Answer 1

The best way to determine where your nodes are making contact is to turn on Physics.
Open GameViewController.swift and enter the following code:
skView.showsPhysics = true

Answer 2

You are experiencing this issue because of this line:
ball.physicsBody = SKPhysicsBody(circleOfRadius: self.frame.size.width / 2)
self is a scene here.
You need this:
ball.physicsBody = SKPhysicsBody(circleOfRadius: ball.frame.size.width / 2)
Turn on physics visual representation in your GameViewController like this:
skView.showsPhysics = true
and you will see what is going on.