Question

我使用Swift with Sprite Kit并且目前有这段代码

class GameScene: SKScene
{
    // properties
    var mySprite: SKSpriteNode?
    //////////////////////////

    ...

    func initSprite()
    {
        let randomNumber = GenerateRandomNum() // some rand 0-2

        switch randomNumber
        {
            case 0:
                mySprite = SKSpriteNode(imageNamed: "sprite1")
                mySprite.position = somePos
                self.addChild(mySprite!)
            case 1:
                mySprite = SKSpriteNode(imageNamed: "sprite2")
                mySprite.position = somePos
                self.addChild(mySprite!)
            case 2:
                mySprite = SKSpriteNode(imageNamed: "sprite3")
                mySprite.position = somePos
                self.addChild(mySprite!)
            default:
                println("Error")
        }

    }

}

我想将self.addChild(mySprite!)放在switch语句的外部和下方，这样我就不必每次都在每个案例中都写出来。但问题是，如果我在switch语句之外写，我因initSprite()

而致电"found nil while unwrapping an Optional value".时出现运行时错误

如何更好地编写此代码，以便在每种情况下都不必编写self.addChild(mySprite!)？

Answer 1

lazy var怎么样？

class GameScene: SKScene
{
    // properties
    lazy var mySprite: SKSpriteNode = {
        let imageNames = [ "sprite1", "sprite2", "sprite3" ]
        let imageName = imageNames[ arc4random_uniform(3) ]

        let node = SKSpriteNode( imageNamed: imageName )
        self.addChild(node)
        node
    }
}

mySprite 将始终为非零，并将在首次访问时分配。（或者适应不懒惰。）

Answer 2

试试这个：

var mySprite: SKSpriteNode!


func initSprite()
    {
        let randomNumber = GenerateRandomNum() // some rand 0-2

        var imageName = nil // default image name here
        var position = nil // default position here

        switch randomNumber
        {
            case 0:
                imageName = "sprite1"
                position = pos
            case 1:
                imageName = "sprite1"
                position = pos
            case 2:
                imageName = "sprite1"
                position = pos
            default:
                println("Error")
        }
        if imageName != nil && position != nil
        {
           mySprite = SKSpriteNode(imageNamed: imageName)
           mySprite.position = position
           self.addChild(mySprite!)
        }
    }

这里有一次SKSpriteNode设置完成，并且不要忘记提供默认值，如果不需要默认值，则在创建精灵时进行空检查。

对可选属性感到困惑 - 如何更好地编写此代码？

2 个答案: