Objective-C 到 Swift 的完成处理程序

Question

我目前正在重写一个项目，从 Objective-C 到 Swift。大部分项目已完成，但我在翻译具有完成处理程序的方法时遇到问题。我已经查看了文档，但我仍然遇到问题。方法是：

- (void)start:(void ( ^ ) ( WTStartupConfiguration *configuration ))startupHandler 
completion:(void ( ^ ) ( BOOL isRunning , NSError *error ))completionHandler

在objective-C中，我会简单地写成：

[self.architectView start:^(WTStartupConfiguration *configuration)
 { } completion:^(BOOL isRunning, NSError *error) {}}];

我无法很好地掌握 Swift 中的闭包语法。如有任何帮助，我们将不胜感激！

Answer 1

你的函数需要这样的东西：

func start(startupHandler:(configuration: WTStartupConfiguration)->(), completion:(isRunning:Bool, error:NSError?)->()) {

    let configuration = WTStartupConfiguration() // create your configuration

    startupHandler(configuration:configuration) // call your startup handler closure

    ... // do some stuff

    let isRunning = false // replace with actual logic
    let error = nil // replace with your actual error detection

    completion(isRunning: isRunning, error: error) // call completion closure
}

你可以这样称呼它：

start(
    { configuration in

        // do something with your configuration

    }, completion: {isRunning, error in

        // do something with your isRunning & error.

})

闭包使用语法 (arguments) -> (returns) 定义，您可以将 arguments 替换为您的输入，将 return 替换为您的 [=20] =]（很像函数的定义方式）。

在你的例子中，你的闭包没有 return 任何东西，所以我们将它们定义为：

(isRunning:Bool, error:NSError?) -> ()

（其中空元组 () 用于表明没有 returned）

然后创建它们，并使用简写符号将它们传递给函数（如果闭包的参数类型已知）：

closureArgument: { (arguments here, without types as they're known) in

}

closureArgument: { isRunning, error in 

}

将它们传递给函数的更正式的方式是：

closureArgument: { (arguments with types) -> (returns with types) in

}

closureArgument: { (isRunning:Bool, error:NSError?) -> () in 

}

然后您可以用与调用函数几乎相同的方式调用闭包。

closureArgument(isRunning: false, error: nil)

我发现 this site 非常适合作为闭包语法的参考（并且可能比我解释得更好）。

Answer 2

为了让您了解闭包的工作原理，我将闭包的定义分开，而不是将其内联定义到方法签名中。您可以执行以下操作：

func start(startupHandler: (configuration: WTStartupConfiguration) -> Void, completion: (isRunning: Bool, error: NSError) -> Void ) {
    //Your code for start method
}

var startupHandlerClosure = { (configuration: WTStartupConfiguration) -> Void in
    //Your code for startupHandler closure
}

var completionClosure = { (isRunning: Bool, error: NSError) -> Void in
    //Your code for completion closure
}

//Method call
start(startupHandlerClosure, completion: completionClosure)

@originaluser2 打败了我。他提供了带有附加代码的示例。

Answer 3

我相信其他人会通过示例代码为您提供非常详细的答案，所以我只提一下以供将来参考：

如何在 Swift 中声明闭包？

来自 fuckingclosuresyntax.com or the SFW version goshdarnclosuresyntax.com.

As a variable:
var closureName: (ParameterTypes) -> (ReturnType)
As an optional variable:
var closureName: ((ParameterTypes) -> (ReturnType))?
As a type alias:
typealias ClosureType = (ParameterTypes) -> (ReturnType)
As a constant:
let closureName: ClosureType = { ... }
As an argument to a function call:
func({(ParameterTypes) -> (ReturnType) in statements})
As a function parameter:
array.sort({ (item1: Int, item2: Int) -> Bool in return item1 < item2 })
As a function parameter with implied types:
array.sort({ (item1, item2) -> Bool in return item1 < item2 })
As a function parameter with implied return type:
array.sort({ (item1, item2) in return item1 < item2 })
As the last function parameter:
array.sort { (item1, item2) in return item1 < item2 }
As the last parameter, using shorthand argument names:
array.sort { return [=19=] <  }
As the last parameter, with an implied return value:
array.sort { [=20=] <  }
As the last parameter, as a reference to an existing function:
array.sort(<)
As a function parameter with explicit capture semantics:
array.sort({ [unowned self] (item1: Int, item2: Int) -> Bool in return item1 < item2 })
As a function parameter with explicit capture semantics and inferred parameters / return type:
array.sort({ [unowned self] in return item1 < item2 })
This site is not intended to be an exhaustive list of all possible uses of closures.

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