如何從早期一個init在迅速3

Question

返回我有一個應用程序中，我想創建一個基於是否已經有保存到用戶的默認等同對象的對象。如果檢測到對象，我想在類init中檢測到它並提前返回。這就是我要做的：

init() { 

    /* There are two possibilities when creating a hero: 
    1. The hero is brand new and needs to be built from scratch 
    2. The hero is loaded from defaults */ 

    // Check to see if there is existing game data: 

    if defaultExistsForGameData() { 
     // This means there is a hero to load and no need to create a new one 
     self = extractHeroFromDefaults() // This just loads from UserDefaults 
     print("Loading hero from defaults with name of: \(hero.heroName).") 

     return self 
    } 

    // These actions are for creating a brand new hero 
    let size = CGSize(width: 32, height: 32) 
    let heroTexture = SKTexture(imageNamed: "hero2.ico") 
    super.init(texture: heroTexture, color: .clear, size: size) 

    self.isUserInteractionEnabled = true 
    self.name = "hero" 

    self.zPosition = 50 

} 

有在控制檯一對夫婦的錯誤，自己是不可改變的，等我想知道這是否是一個有效的模式是什麼，或者我應該完全考慮不同的方法。

Answer 1

在Swift中（與ObjC不同），init無法返回與自身不同的對象。實現你想要做的事情的一種常見方法是使用類工廠方法（如果不希望其他對象能夠直接調用它，可選地使其爲init）。

例如，沿着這些路線的東西：

class func loadOrCreate() -> Hero { 
    if defaultExistsForGameData() { 
     // This means there is a hero to load and no need to create a new one 
     print("Loading hero from defaults with name of: \(hero.heroName).") 
     return extractHeroFromDefaults() // This just loads from UserDefaults 
    } else { 
     return Hero() 
    } 
} 

private init() { 
    let size = CGSize(width: 32, height: 32) 
    let heroTexture = SKTexture(imageNamed: "hero2.ico") 
    super.init(texture: heroTexture, color: .clear, size: size) 

    self.isUserInteractionEnabled = true 
    self.name = "hero" 

    self.zPosition = 50 
} 

另一種方法更接近當前的API是創建一個單獨的（可能是私人）指定初始化是這樣的：

private init(name: String, zPosition: Int) { 
    let size = CGSize(width: 32, height: 32) 
    let heroTexture = SKTexture(imageNamed: "hero2.ico") 
    super.init(texture: heroTexture, color: .clear, size: size) 

    self.isUserInteractionEnabled = true 
    self.name = name 
    self.zPosition = zPosition 
} 

public convenience init() { 
    let name: String 
    let zPosition: Int 
    if defaultExistsForGameData() { 
     name = defaultName() // Read it out of user defaults 
     zPosition = defaultZPosition 
    } else { 
     name = "hero" 
     zPosition = 50 
    } 
    self.init(name: name, zPosition: zPosition) 
} 

的這種方法的一個問題是它可能有點令人驚訝。如果您創建多個Hero對象，則不清楚應該發生什麼。像loadOrCreate()這樣的東西很清楚地表明有外部影響。