swift - 为什么这个闭包没有我期望的参数？

Question

我有一个 SettingsViewController 并创建了一个结构来定义每个设置所需的信息。

///Represents a list of the options needed to populate a `SettingsTableViewCell`
public struct Setting {
    ///The image to use for the icon
    var imageName : String

    ///The text to display as the title of the setting
    var title : String

    ///Called when the switch is tapped. If no closure is supplied, the switch is hidden
    var switchCallback: ((_ status: Bool)->())?
}

View Controller 保留这些设置的数组，以便稍后在 TableView 中使用。下面提供了一个示例:

let options : [Setting] =
[
    Setting(imageName: "notifications", title: "Bump Notifications") {updateNotificationSetting($0)},
    ...
]

但是，当我尝试编译时，出现错误:

Cannot convert value of type '(SettingsViewController) -> (Bool) -> ()' to expected argument type '((Bool) -> ())?'

有人可以解释一下 (SettingsViewController) 的来源吗？如果可以的话，请问我需要更改什么来修复它？

---

对于 SSCCE，请参见下文:

import UIKit

///Represents a list of the options needed to populate a `SettingsTableViewCell`
public struct Setting {
    ///The image to use for the icon
    var imageName : String

    ///The text to display as the title of the setting
    var title : String

    ///Called when the switch is tapped. If no closure is supplied, the switch is hidden
    var switchCallback: ((_ status: Bool)->())?
}



@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    let options : [Setting] =
    [
        //Error is on the following line
        Setting(imageName: "notifications", title: "Bump Notifications") {isOn in updateSetting(isOn)},
    ]

    func updateSetting(isOn : Bool) {

    }

}

Answer 1

Setting 初始化器中的闭包正在捕获 self。但是，Swift中的self只有在对象的所有属性都初始化后，即let options初始化后才可用。

打破循环的一种方法是使用属性的惰性初始化:

public struct Setting {
    var imageName : String
    var title : String
    var switchCallback: ((_ status: Bool)->())?
}

class MyClass {
    lazy var options: [Setting] = [
        Setting(imageName: "x", title: "X") { [unowned self] in self.updateSetting(isOn: $0)}
    ]

    func updateSetting(isOn : Bool) {}
}

请注意显式类型 : [Setting] 目前是声明所必需的。

请注意，您需要使用 [unowned self] 或 [weak self] 来打破发布周期(感谢@rob 的评论)。