可选的关闭并检查它是否为零

Question

所以我想拥有的是一个可以在函数中传递给它的闭包的类,它也可能在某个时候想要忽略那个闭包.如何检查闭包变量是否已设置,我可以在完成后删除它吗？

无法使用类型'的参数列表调用'!='(@lvalue(sucsess:Bool!,products:[AnyObject]!) - >()？,NilLiteralConvertible)'Type'(sucsess:Bool!,产品:[AnyObject] ]!) - >()？' 不符合协议'NilLiteralConvertible'

class someClass{
    //typealias completionHandlerClosureType = (sucsess:Bool!, items:[AnyObject]!)->()
    var completionHandler:(sucsess:Bool!, items:[AnyObject]!)->()?
    var hitpoints = 100
    var someset = ["oh no!","avenge me!"]
    init(){}

    func getHitFunc(impact:Int, passedCompletionsHandler:(sucsess:Bool!, items:[AnyObject]!)->()){
        completionHandler = passedCompletionsHandler
        hitpoints = hitpoints - impact
    }

    func checkIfDead{
        if hitpoints<=0 {               // The error received
            if completionHandler != nil{// Cannot invoke '!=' with an argument list of type 
                                        //'(@lvalue (sucsess: Bool!, products: [AnyObject]!) -> ()?, NilLiteralConvertible)' 
                //run the handler if dead
                completionHandler(sucsess: true, items: someset)
                //do not run it again
                completionHandler = nil     //Type '(sucsess: Bool!, products: [AnyObject]!) -> ()?' does not conform to protocol 'NilLiteralConvertible'
            }
        }
        else{
            completionHandler = nil      //Type '(sucsess: Bool!, products: [AnyObject]!) -> ()?' does not conform to protocol 'NilLiteralConvertible'
        }
    }
}

Answer 1

您需要将括号中的闭包签名包装起来以使闭包本身可选.现在它的编写方式,闭包返回一个可选的Void(这没有多大意义).

var completionHandler: ((sucsess:Bool!, items:[AnyObject]!)->())?

您的示例代码的一些样式点和修订:

 // Capitalize class names so it's clear what's a class 
class SomeClass {
    // "success" has two "c"s
    var completionHandler: ((success:Bool!, items:[AnyObject]!)->())?
    var hitpoints = 100
    var someset = ["oh no!","avenge me!"]

    init() { }

    func getHitFunc(impact:Int, passedCompletionsHandler:(success:Bool!, items:[AnyObject]!)->()){
        completionHandler = passedCompletionsHandler
        hitpoints = hitpoints - impact
    }

    // You were missing the argument list here:
    func checkIfDead() {
        if hitpoints <= 0 {

            // Rather than checking to see if the completion handler exists, you can
            // just call it using optional syntax like this:
            completionHandler?(success: true, items: someset)
        }
        completionHandler = nil
    }
}

Answer 2

首先,在完成处理程序的声明中,您需要使用括号将整个事物声明为可选:

var completionHandler: ((_ success: Bool, _ items: [Any]?) -> ())?

或者,或许更好,您可以用以下内容替换最终()结果Void:

var completionHandler: ((_ success: Bool, _ items: [Any]?) -> Void)?

另外,请注意,我认为您不打算使用Bool可选项(因为如果闭包存在,您可能总是传递success值true或false).显然,这些数组很items可能是可选的.

无论如何,完成后,您只需确保解开该可选项:

func checkIfDead() {
    if hitpoints <= 0 {
        completionHandler?(true, items)
    }
    completionHandler = nil
}

当且仅当它不是时nil,它执行闭包,避免显式检查是否存在nil.

对于它的价值,这可能是你typealias可能会减少混淆的情况:

typealias CompletionHandlerClosureType = (_ success: Bool, _ items: [Any]?) -> Void

然后该属性简单:

var completionHandler: CompletionHandlerClosureType?

将此completionHandler作为可选参数的函数可以:

func startSomeProcess(passedCompletionHandler: CompletionHandlerClosureType?) {
    completionHandler = passedCompletionHandler
    // do whatever else you want
}

然后最终完成逻辑不变:

func finishSomeProcess() {
    completionHandler?(true, items)
    completionHandler = nil
}

(注意,以上内容已针对Swift 3进行了修改.如果您想查看Swift 2再现,请参阅此答案的上一版本.)