在闭包参数Swift中添加[unown self] [英] Add [unowned self] to the closure argument Swift

问题描述

我有一个带有完成处理程序的函数，返回一个或多个参数.

I have a function with a completion handler, returning one parameter or more.

在客户端中，当执行完成处理程序时，我想拥有对self的unowned引用，并且可以访问传递的参数.

In a client, when executing a completion handler, I'd like to have an unowned reference to self, as well as having access to the parameter passed.

这是一个Playground示例，说明了我要解决的问题和目标.

Here is the Playground example illustrating the issue and the goal I'm trying to achieve.

import UIKit

struct Struct {
  func function(completion: (String) -> ()) {
    completion("Boom!")
  }

  func noArgumentsFunction(completion: () -> Void) {
    completion()
  }
}

class Class2 {
  func execute() {
    Struct().noArgumentsFunction { [unowned self] in
      //...
    }

    Struct().function { (string) in // Need [unowned self] here
      //...
    }
  }
}

推荐答案

正如我在评论中所说

Struct().function { [unowned self] (string) in 
    //your code here 
}

捕获列表和闭包参数应该是闭包中的顺序更多信息，请参见

Capture list and closure parameters that should be the order in closures more info from Apple Documentation

定义捕获列表

捕获列表中的每个项目都是一对 弱引用或无所有权关键字，引用了类实例(例如 作为self)或使用某些值初始化的变量(例如委托= self.delegate！).这些配对写在一对正方形内 花括号，用逗号分隔.

Each item in a capture list is a pairing of the weak or unowned keyword with a reference to a class instance (such as self) or a variable initialized with some value (such as delegate = self.delegate!). These pairings are written within a pair of square braces, separated by commas.

将捕获列表放置在闭包的参数列表之前，然后返回 输入是否提供:

Place the capture list before a closure’s parameter list and return type if they are provided:

lazy var someClosure: (Int, String) -> String = {
    [unowned self, weak delegate = self.delegate!] (index: Int, stringToProcess: String) -> String in
    // closure body goes here 
}

如果闭包没有指定参数列表或返回类型，因为 他们可以从 在上下文中，将捕获列表放置在关闭的最开始处， 后跟in关键字:

If a closure does not specify a parameter list or return type because they can be inferred from context, place the capture list at the very start of the closure, followed by the in keyword:

lazy var someClosure: () -> String = {
     [unowned self, weak delegate = self.delegate!] in
     // closure body goes here
 }

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