ios - 从委托(delegate)返回元组(可选类型的值未展开)

Question

我已经定义了一个带有返回元组方法的协议(protocol):

protocol SMCalculatorDelegate {

    func numbersToAdd() -> (Int, Int)

}

当我尝试像这样针对我的类中的委托(delegate)方法调用它时:

class SMCalculator: NSObject {

    var delegate : SMCalculatorDelegate?

    func add() {

        let myTuple : (n1: Int, n2: Int) = delegate?.numbersToAdd()

    }

}

我在引用该行代码的 .numbersToAdd() 部分的 let myTuple... 开头的行中收到以下错误。

"Value of optional type '(Int, Int)?' not unwrapped; did you mean to use '!' or '?'?"

当我可以像这样毫无错误地提取元组时，为什么这不起作用？

let tuple = delegate?.numbersToAdd()

println(tuple) //Prints (5,5)

Answer 1

我仍在努力掌握一切，但这似乎是正确的行为。

如果 delegate 为 nil，您会将 nil 分配给 myTuple，因此您也需要将 myTuple 设为可选...

class SMCalculator: NSObject {

   var delegate : SMCalculatorDelegate?

   func add() {

       let myTuple : (n1: Int, n2: Int)? = delegate?.numbersToAdd()

       // this works, because we're saying that myTuple definitely isn't nil
       println(myTuple!.n1)

       // this works because we check the optional value
       if let n1 = myTuple?.n1 {
           println(n1)
       } else {
           println("damn, it's nil!")
       }

       // doesn't work because you're trying to access the value of an optional structure
       println(myTuple.n1)

   } 

}

对我有用