Swift spriteKit didBeginContact无法添加Child

我正在用SpriteKit解决一些碰撞检测问题。我在didBeginContact中触发了正确的碰撞，这很好

现在，我遇到了一个范围问题，我无法根据一次碰撞在场景中删除和添加子对象。第一次检测确实有效，但第二次检测失败

下面是正确调用的didBeginContact函数。这两种方法都在我的根场景中：

func didBeginContact(contact: SKPhysicsContact) {        
    if (contact.bodyA.categoryBitMask == ColliderType.Head && contact.bodyB.categoryBitMask == ColliderType.Food) {            
        //remove and place new food
        //this one works great
        self.placeFoodInRandomGridLocation()
    } else if (contact.bodyA.categoryBitMask == ColliderType.Food && contact.bodyB.categoryBitMask == ColliderType.Body) {
        //remove and place new food
        //this one FAILS
        self.placeFoodInRandomGridLocation()
    }
}

func placeFoodInRandomGridLocation() {
    snakeFood!.removeFromParent()
    let randomX = arc4random_uniform((myGrid.columnCount))
    let randomY = arc4random_uniform((myGrid.rowCount))
    snakeFood = Food(size: CGSize(width: myGrid.snakeWide/2, height: myGrid.snakeHigh/2), gap: gapFactor)
    snakeFood!.position = CGPoint(x: colLines[Int(randomX)], y: rowLines[Int(randomY)])
    //THIS child does not appear for the 2nd collision. It DOES for the first.
    self.addChild(snakeFood!)
}

struct ColliderType {
    static let Head:          UInt32 = 0
    static let Food:          UInt32 = 0b1
    static let Body:          UInt32 = 0b10
}

---

在didBeginContact碰撞触发后，我无法直接更新蛇食对象的位置。我能够在didBeginContact中跟踪布尔值，然后在didBeginContact中捕获。此解决方案效果良好：

func didBeginContact(contact: SKPhysicsContact) {
    if (contact.bodyA.categoryBitMask == ColliderType.Head && contact.bodyB.categoryBitMask == ColliderType.Food) {
        placeFood = true
    } else if (contact.bodyA.categoryBitMask == ColliderType.Food && contact.bodyB.categoryBitMask == ColliderType.Body) {
        placeFood = true
    } else if (contact.bodyA.categoryBitMask == ColliderType.Body && contact.bodyB.categoryBitMask == ColliderType.Food) {
        placeFood = true
    }

}

func placeFoodInRandomGridLocation() {
    let randomX = arc4random_uniform(UInt32(myGrid.columnCount))
    let randomY = arc4random_uniform(UInt32(myGrid.rowCount))
    snakeFood!.position = CGPoint(x: colLines[Int(randomX)], y: rowLines[Int(randomY)])
}

override func didSimulatePhysics() {
    if (placeFood == true) {
        placeFood = false
        placeFoodInRandomGridLocation()
    }
}

---

注意，我也尝试过仅仅定位蛇食，而不是移除和添加。这也失败了。你确定在else中，如果bodyA是食物，而不是身体？我建议测试哪个位掩码的值较低，然后将其与值较低的ColliderType进行比较。我还应该确定两个冲突都成功地调用了placefoodinrandomgrid location方法。您能发布位掩码值的声明吗？添加了位掩码值。另外请注意，我不再添加子级。我只是重新定位。