swift 2 fatal error : unexpectedly found nil while unwrapping an Optional value - Category Name

Question

我在以下代码中不断收到“ fatal error :在展开可选值时意外发现 nil”

let ballCategoryName =  "ball"


class GameScene: SKScene, SKPhysicsContactDelegate {
    override func didMoveToView(view: SKView) {

    let borderBody = SKPhysicsBody(edgeLoopFromRect: self.frame)
    borderBody.friction = 0
    self.physicsBody = borderBody


    let ball = childNodeWithName(ballCategoryName) as! SKSpriteNode
    ball.position = CGPointMake(self.size.width / 2, self.size.height / 2)
    ball.physicsBody?.dynamic = true
    ball.physicsBody = SKPhysicsBody(circleOfRadius: ball.size.height / 2)
    ball.physicsBody!.applyImpulse(CGVector(dx: 2.0, dy: -2.0))

    self.addChild(ball)

错误出现在 "let ball = childNodeWithName(ballCategoryName) as!SKSpriteNode" 想知道是否有人可以帮助我解决为什么会出现这种情况

Answer 1

您必须将该球创建为一个节点。您可以像这样创建一个节点:

let ball = SKSpriteNode(imageNamed: "fileimage.png")

然后将其添加到场景中。

问题是您不知从何处创造了那个球。如果您还没有创建该场景，您将不会在下面找到任何内容。那个 child 不存在。

childNodeWithName(ballCategoryName) as! SKSpriteNode