SKPhysics doBeginContact（）不使用基本游戏

Question

我已经构建了一个依赖于SKPhysics的游戏来检测玩家和随机生成的墙之间的碰撞。出于某种原因，SKPhysics didBeginContact（）无效。我已经在其中添加了一个print语句，但它根本没有运行。我已将物理添加到wall类和播放器类，但结果是相同的。如果你发现任何突然出现的事，请告诉我。
代码：
GameScene.swift

//
//  GameScene.swift
//  marioRunner
//
//  Created by nick on 11/18/15.
//  Copyright (c) 2015 Supreme Leader. All rights reserved.
//

import SpriteKit

class GameScene: SKScene, SKPhysicsContactDelegate {

    var movingGround: MLMovingGround!
    var hero: MLHero!
    var wallGenerator: MLWallGenerator!
    var isStarted = false

    override func didMoveToView(view: SKView) {
        backgroundColor = UIColor(red: 159.0/255.0, green: 201.0/255.5, blue: 244.0/255.0, alpha: 1.0)
        movingGround = MLMovingGround(size: CGSizeMake(view.frame.width, 20))
        movingGround.position = CGPointMake(0, view.frame.size.height/2)
        addChild(movingGround)

        self.hero = MLHero()
        hero.position = CGPointMake(70, movingGround.position.y + movingGround.frame.size.height/2 + hero.frame.size.height/2)
        self.addChild(hero)

        wallGenerator = MLWallGenerator(color: UIColor.clearColor(), size: view.frame.size)
        wallGenerator.position = view.center
        addChild(wallGenerator)
        physicsWorld.contactDelegate = self
    }

    func start() {
        isStarted = true
        movingGround.start()
        wallGenerator.startGeneratingWallsEvery(1)
        hero.flip()
    }

    func gameOver() {
        hero.stop()
    }


    func didBeginContact(contact: SKPhysicsContact) {
        //gameOver()
        hero.body.color = UIColor.orangeColor()
        print("HIT")
    }

    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
        if isStarted == false{
            start()
        } else {
            hero.flip()
        }
    }

    override func update(currentTime: CFTimeInterval) {

    }
}

Wall Class

//
//  MLWall.swift
//  marioRunner
//
//  Created by nick on 12/9/15.
//  Copyright © 2015 Supreme Leader. All rights reserved.
//

import Foundation
import SpriteKit

class MLWall: SKSpriteNode {

    let WALL_WIDTH: CGFloat = 30.0
    let WALL_HEIGHT: CGFloat = 50.0
    let WALL_COLOR = UIColor.blackColor()

    init() {
        let size = CGSizeMake(WALL_WIDTH, WALL_HEIGHT)
        super.init(texture: nil, color: WALL_COLOR, size: size)
        loadPhysicsBodyWithSize(size)
        startMoving()
    }

    func loadPhysicsBodyWithSize(size: CGSize) {
        physicsBody = SKPhysicsBody(rectangleOfSize: size)
        physicsBody?.categoryBitMask = wallCategory
        physicsBody?.affectedByGravity = false
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    func startMoving() {
        let moveLeft = SKAction.moveByX(-300, y:0, duration:1)
        runAction(SKAction.repeatActionForever(moveLeft))
    }
}

英雄课

//
//  MLHero.swift
//  marioRunner
//
//  Created by nick on 12/7/15.
//  Copyright © 2015 Supreme Leader. All rights reserved.
//

import Foundation
import SpriteKit

class MLHero: SKSpriteNode {
    var body: SKSpriteNode!
    var arm: SKSpriteNode!
    var leftFoot: SKSpriteNode!
    var rightFoot: SKSpriteNode!
    var isUpsideDown = false
    init() {
        super.init(texture: nil, color: UIColor.clearColor(), size: CGSizeMake(32, 44))
        loadPhysicsBodyWithSize(size)
        body = SKSpriteNode(color:UIColor.redColor(), size: CGSizeMake(self.frame.size.width, 40))
        body.position = CGPointMake(0, 2)
        addChild(body)
        let skinColor = UIColor(red:207.0/255.0, green:193.0/255.0, blue: 168.0/255.0, alpha: 1.0)
        let face = SKSpriteNode(color: skinColor, size: CGSizeMake(self.frame.size.width, 2))
        face.position = CGPointMake(0, 6)
        body.addChild(face)
        let eyeColor = UIColor.whiteColor()
        let leftEye = SKSpriteNode(color: eyeColor, size: CGSizeMake(6,6))
        let rightEye = leftEye.copy() as! SKSpriteNode
        let pupil = SKSpriteNode(color: UIColor.blackColor(), size: CGSizeMake(3,3))
        pupil.position = CGPointMake(2, 0)
        leftEye.addChild(pupil)
        rightEye.addChild(pupil.copy() as! SKSpriteNode)
        leftEye.position = CGPointMake(-4, 0)
        face.addChild(leftEye)
        rightEye.position = CGPointMake(14, 0)
        face.addChild(rightEye)
    }
    /*func performOneRunCycle() {
        let up = SKAction.moveByX(0, y: 2, duration: 0.05)
        let down = SKAction.moveByX(0, y: -2, duration: 0.05)
    }*/

    func loadPhysicsBodyWithSize(size: CGSize) {
        physicsBody = SKPhysicsBody(rectangleOfSize: size)
        physicsBody?.categoryBitMask = heroCategory
        physicsBody?.contactTestBitMask = wallCategory
        physicsBody?.affectedByGravity = false
    }

    func flip() {
        isUpsideDown = !isUpsideDown
        var scale: CGFloat
        if isUpsideDown {
            scale = -1.0
        } else {
           scale = 1.0
        }
        let translate = SKAction.moveByX(0, y: scale*(size.height + kMLGroundHeight), duration: 0.1)
        let flip = SKAction.scaleYTo(scale, duration: 0.1)

        runAction(translate)
        runAction(flip)
    }

    func stop() {
        //body.removeAllActions()
        print("stopped")
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

}

Constants.swift

//
//  constants.swift
//  marioRunner
//
//  Created by nick on 12/10/15.
//  Copyright © 2015 Supreme Leader. All rights reserved.
//

import Foundation
import UIKit

let kMLGroundHeight: CGFloat = 20.0
let kdefaultXToMovePerSecond: CGFloat = 320.0
let heroCategory: UInt32 = 0x1 << 0
let wallCategory: UInt32 = 0x1 << 1

谢谢， 尼克