swift - 快速测试节点是否附加到物理主体

Question

我在检测到 SKSpriteNode 之间的接触时调用的函数中获取附加到接触体 (SKPhysicsBody) 的节点。有时，我会收到错误，因为它无法将节点附加到接触体，因此我测试是否有一个节点可以避免此类错误。但警告告诉我它永远不会返回 false。自从我测试以来，我再也没有遇到过这样的错误，但我不确定它是否运行良好或者是否仍然会发生。你有什么想法吗？

//The actual code
func didBegin(_ contact: SKPhysicsContact) {
    if (contact.bodyA.categoryBitMask == enemyCategory) && (contact.bodyB.categoryBitMask == shootCategory){ //test if it is the contact with I want to catch
        let shootNode = contact.bodyB.node, shootNode != nil { // I test if there's a node attached to the enemyShootNode but it's supposed never to return false
            let enemyNode = contact.bodyA.node, enemyNode != nil { // I test if there's a node attached to the shootNode but it's supposed never to return false
                let enemySKNode = enemyNode as? SKSpriteNode
                let shootSKNode = shootNode as? SKSpriteNode
                // code
            }
        }
    }
}

   // The code with error
func didBegin(_ contact: SKPhysicsContact) {
    if (contact.bodyA.categoryBitMask == enemyCategory) && (contact.bodyB.categoryBitMask == shootCategory){
        let shootNode = contact.bodyB.node!
        let enemyNode = contact.bodyA.node! // The error occurs here : "fatal error: unexpectedly found nil while unwrapping an Optional value"
        let enemySKNode = enemyNode as? SKSpriteNode
        let shootSKNode = shootNode as? SKSpriteNode
     }
}

Answer 1

感谢您的建议，错误确实来自 SKPhysics 属性(didBegin 函数被调用了几次)，但我没有设法修复。虽然我纠正了检查 Sprite 是否在这里的方式，并且没有更多警告或错误，所以我认为它工作得很好:

func didBegin(_ contact: SKPhysicsContact) {
    if (contact.bodyA.categoryBitMask == enemyCategory) && (contact.bodyB.categoryBitMask == shootCategory) || (contact.bodyA.categoryBitMask == shootCategory) && (contact.bodyB.categoryBitMask == enemyCategory){
        if var shootNode = contact.bodyB.node{
            if var enemyNode = contact.bodyA.node{
                // If the enemyNode and the shootNode don't respectively correspond to 
                if contact.bodyA.categoryBitMask == shootCategory {
                    shootNode = contact.bodyA.node!
                    enemyNode = contact.bodyB.node!
                }
                let enemySKNode = enemyNode as? SKSpriteNode
                let shootSKNode = shootNode as? SKSpriteNode
            }
        }
    }
}