swift - 为什么不能使用 SKShapenode 的子类？

Question

我在这里使用了一个名为 Enemy 的子类，它继承自 SKShapeNode，这里的问题是当我检查 bullet 和 enemy 我捕获了敌人的 health 它说 found nil while unwrapping。

这是我的代码:

private func drawEnemy() {
        let (color, edge) = randomColorandEdge()
        let nextEnemyPosition = determineNextEnemyPosition(edge: Int(edge))
        let enemyPosition = spawnAtRandomPosition(edge: nextEnemyPosition)
        let enemyCircle = Enemy(scene: self, color: color, radius: globalRadius, position: enemyPosition)
        let enemy = enemyCircle.drawEnemy()
        world.addChild(enemy)
        numberOfEnemies += 1
        enemy.name = String(numberOfEnemies)
        runToCenter(enemy: enemy)
    }

func didBegin(_ contact: SKPhysicsContact) {
if (contact.bodyB.categoryBitMask == bodyType.bullet.rawValue) && (contact.bodyA.categoryBitMask == bodyType.enemy.rawValue) {
            let hitter = contact.bodyB.node as? SKShapeNode
            let enemy = contact.bodyA.node as? Enemy
            hitter?.removeFromParent()
            let health = enemy?.getHealth()
            if health! > 0 {
                enemy?.setHealth(amount: health! - 1)
            }else {
                enemy?.removeFromParent()
            }
        }
    }

这是我的Enemy 类:

class Enemy: SKShapeNode {

    private var health: Int = 5
    private var color: SKColor!
    private var radius: CGFloat!
    private var s: SKScene!
    private var pos: CGPoint!
    private var enemy: SKShapeNode!

    init(scene: SKScene, color: SKColor, radius: CGFloat, position: CGPoint) {
        self.color = color
        self.radius = radius
        self.health = 5
        self.s = scene
        self.pos = position
        super.init()
    }

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

    func setHealth(amount: Int) {
        self.health = amount
    }

    func getHealth() -> Int {
        return self.health
    }

    func drawEnemy() -> SKShapeNode {
        enemy = SKShapeNode(circleOfRadius: radius)
        enemy.fillColor = color
        enemy.glowWidth = 0.5
        enemy.strokeColor = color
        enemy.physicsBody = SKPhysicsBody(circleOfRadius: radius)
        enemy.physicsBody?.affectedByGravity = false
        enemy.physicsBody?.isDynamic = true
        enemy.physicsBody?.collisionBitMask = GameScene.bodyType.player.rawValue
        enemy.physicsBody?.categoryBitMask = GameScene.bodyType.enemy.rawValue
        enemy.physicsBody?.contactTestBitMask = GameScene.bodyType.player.rawValue
        enemy.physicsBody?.usesPreciseCollisionDetection = true
        enemy.position = pos
        return enemy
    }

}

当我在 didBegin 函数中检查 health 是否大于 0 时出现错误

Answer 1

您没有正确地子类化，您将 Enemy 对象用作工厂和实例，将两者分开。

工厂:

public class EnemyFactory
{
    public func createEnemy(color: SKColor, radius: CGFloat, position: CGPoint) -> Enemy{
        let enemy = Enemy(circleOfRadius: radius)
        enemy.setup(color:color, radius: radius, position: position)
        return enemy
    }
}

实例类:

public class Enemy: SKShapeNode {
    static let Factory = EnemyFactory()
    public var health: Int = 5

    func setup (color: SKColor, radius: CGFloat, position: CGPoint) {
        self.position = position
        fillColor = color
        glowWidth = 0.5
        self.health = 5
        strokeColor = color
        let physicsBody = SKPhysicsBody(circleOfRadius: radius)
        physicsBody.affectedByGravity = false
        physicsBody.isDynamic = true
        physicsBody.collisionBitMask = GameScene.bodyType.player.rawValue
        physicsBody.categoryBitMask = GameScene.bodyType.enemy.rawValue
        physicsBody.contactTestBitMask = GameScene.bodyType.player.rawValue
        physicsBody.usesPreciseCollisionDetection = true
        self.physicsBody = physicsBody
    }
    override init(){
        super.init()

    }

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

我采取了一些自由:我删除了局部冗余变量，如颜色和场景，你可以直接从对象中获取这些变量，不需要另一个变量来保存它们。您也不需要 getter 和 setter，Swift 已经为您做好了。