swift – 可选闭包,并检查它是否为nil

概述所以我想要的是一个类，可能会得到一个闭包传递给它在一个函数，它也可能在某些时候想忽略一个闭包。如何检查闭包变量是否设置和hwo可以删除它，当我完成它？ Cannot invoke ‘!=’ with an argument list of type ‘(@lvalue (sucsess: Bool!, products: [AnyObject]!) -> ()?, NilLiteralConver 所以我想要的是一个类，可能会得到一个闭包传递给它在一个函数，它也可能在某些时候想忽略一个闭包。如何检查闭包变量是否设置和hwo可以删除它，当我完成它？

Cannot invoke ‘!=’ with an argument List of type ‘(@lvalue (sucsess:
Bool!,products: [AnyObject]!) -> ()?,NilliteralConvertible)’ Type
‘(sucsess: Bool!,products: [AnyObject]!) -> ()?’ does not conform to
protocol ‘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!,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'        }    }}

你需要在括号中包装你的闭包签名，使闭包本身是可选的。现在写的方式，闭包返回一个可选的VoID(这不是真的有意义)。

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

您的示例代码的一些样式点和修订版本：

// 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    }}

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