Swift - 继承自该类的Cast对象

Question

我收到此错误：无法将表达式的类型'（）'转换为键入$'T5' Card从CardCard继承，并且我知道drawRandomCard返回了一个PlayingCard。 如何进行此转换？

var deck = PlayingCardDeck() 
var card = PlayingCard() 

class ViewController: UIViewController { 



override func viewDidLoad() { 
    super.viewDidLoad() 

} 

@IBAction func cardTouchBtn(sender : UIButton) { 

    if !sender.currentTitle{sender.setTitle("", forState: UIControlState.Normal)} 
    if sender.currentTitle.isEmpty{ 
     card = PlayingCard(deck.drawRandomCard()) 
     sender.setBackgroundImage(UIImage(named : "cardFront"), forState: UIControlState.Normal) 
     sender.setTitle(card.contents, forState: UIControlState.Normal) 
    }else{ 
     sender.setBackgroundImage(UIImage(named : "cardBack"), forState: UIControlState.Normal) 
     sender.setTitle("", forState: UIControlState.Normal) 
    } 
} 

} 

上git的全码：https://github.com/victoryudi/CS193p-Swift/tree/master/FlipCard

Answer 1

PlayingCard(...)不是一个演员。这是一个构造函数调用。

如果要投射，请使用deck.drawRandomCard() as PlayingCard。