swift - 球在 Pong Clone 中不动

Question

我的 Pong 版本有问题。当我输入这段代码时，球不会在屏幕上移动。问题出在哪儿？请帮助我!

class GameScene: SKScene {

    var ball = SKSpriteNode()
    var enemy = SKSpriteNode()
    var main = SKSpriteNode()

    override func didMove(to view: SKView) {

        ball = self.childNode(withName: "ball") as! SKSpriteNode
        enemy = self.childNode(withName: "enemy") as! SKSpriteNode
        main = self.childNode(withName: "main") as! SKSpriteNode

        ball.physicsBody?.applyImpulse(CGVector(dx: 20, dy: 20))

        let border  = SKPhysicsBody(edgeLoopFrom: self.frame)

        border.friction = 0
        border.restitution = 1

        self.physicsBody = border

    }
}

Answer 1

你知道这行代码

ball.physicsBody?.applyImpulse(CGVector(dx: 20, dy: 20))

表示

“如果球的属性physicsBody不为nil，调用方法applyImpulse()”

不是吗？好的。如果 physicsBody 是 nil，这段代码会做什么？是的，它什么都不做。那么，您是否在执行此代码时检查过 physicsBody 不是 nil？

根据属性physicsBody的文档:

The default value is nil, which indicates that the node does not participate in the physics simulation at all. If a physics body is provided, when the scene’s physics are simulated, the physics body updates the node’s position and rotates the node.

没有代码显示您在球对象上设置了 physicsBody。