swift - 解包可选错误时意外发现 nil

Question

我正在制作一个基于 Sprite 的游戏。在将物理学应用于我的硬币 Sprite 时，我开始遇到这个错误。关于如何避免它有什么建议吗？

@objc func spawnEnemy(){
    enemy = childNode(withName: "enemy") as? SKSpriteNode
    coin = childNode(withName: "coin") as? SKSpriteNode
    self.physicsWorld.contactDelegate = self

及以后

 for coin in sprites{
    if coin.name == "coin"{
        coin.physicsBody = SKPhysicsBody(rectangleOf: enemy.size)
        coin.physicsBody?.categoryBitMask = PhysicsCategory.coin
          coin.physicsBody?.contactTestBitMask =           PhysicsCategory.player
        coin.physicsBody?.affectedByGravity = false
        coin.physicsBody?.isDynamic = true
        }
}

Answer 1

您应该始终使用“if let”或“guard let”安全地解开可选值

通过使用 if let :

   if let coin = coin , let name = coin.name { 
    // you can use "coin" or "name" safely here
   }else{
     // "coin" or "name" is nil
   }

通过使用guard let:

   guard let coin = coin , let name = coin.name  else { 
     // "coin" or "name" is nil
    return
    }
    //you can use "coin" or "name" safely here