Update Label when 2 SKSpriteNodes collide - sprite-kit

Question

I want to add 1 point to the topLbl whenever the ball collides with the main. How would I do that? Thanks!
import SpriteKit
import GameplayKit
class GameScene: SKScene, SKPhysicsContactDelegate {
var ball = SKSpriteNode()
var main = SKSpriteNode()
var topLbl = SKLabelNode()
var score = [Int]()
override func didMove(to view: SKView) {
startGame()
self.physicsWorld.contactDelegate = self
topLbl = self.childNode(withName: "topLabel") as! SKLabelNode
ball = self.childNode(withName: "ball") as! SKSpriteNode
main = self.childNode(withName: "main") as! SKSpriteNode
ball.physicsBody?.applyImpulse(CGVector(dx: 8, dy: 8))
let border = SKPhysicsBody(edgeLoopFrom: self.frame)
border.friction = 0
border.restitution = 1
self.physicsBody = border
}
func startGame() {
score = [0]
topLbl.text = "\(score[0])"
}
func addScore(byTouch : SKSpriteNode){
if byTouch == main {
score[0] += 1
}
print(score)
}
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
for touch in touches {
let location = touch.location(in: self)
main.run(SKAction.moveTo(x: location.x, duration: 0))
main.run(SKAction.moveTo(y: location.y, duration: 0))
}
}
override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
main.run(SKAction.moveBy(x: 4444, y: 4444, duration: 0))
}
override func update(_ currentTime: TimeInterval) {
// Called before each frame is rendered
}
func didBegin(contact: SKPhysicsContact) {
if (contact.bodyA.categoryBitMask == 1 && contact.bodyB.categoryBitMask == 2) {
if ball == contact.bodyA.node as! SKSpriteNode {
score[0] += 1
}
} else if (contact.bodyA.categoryBitMask == 2 && contact.bodyB.categoryBitMask == 1) {
if ball == contact.bodyB.node as! SKSpriteNode {
score[0] += 1
}
}
}
}