属性声明中的实例方法参考

Question

我想静态地"配置"与BLE相关的类，带有支持的服务，特征，通知处理程序等，带有Typealiases和structs，有点像下面的类。但是，Swift编译器在声明let常数属性时不喜欢我引用实例方法的方式（请参阅badCharacteristics）。做类似此类事情的好方法是什么？必须有一种更迅速的方式来参考实例方法以实现相同的目标。

我考虑过创建一个更削弱的例子，但是我认为一个更真实的示例可能会带来更多的好处。

这是相关编译器错误：Cannot convert value of type to expected argument type

这是代码：

import Foundation
typealias CharacteristicData = NSData
typealias PeripheralName = String?
typealias ServiceId = String
typealias CharacteristicId = String
typealias CharacteristicNotificationHandler = (CharacteristicData, PeripheralName, CharacteristicId) -> Void
private struct SupportedCharacteristic {
    let id: CharacteristicId
    let handler: CharacteristicNotificationHandler?
}
private struct SupportedService {
    let id: ServiceId
    let characteristics: [SupportedCharacteristic]
}
class BleStuff: NSObject {
     /////// This is what I want to do:
     private let badCharacteristics = [SupportedCharacteristic(id: "1000", handler: handler1)]
     // ^^^^ Does not compile:
     // Cannot convert value of type '(BleStuff) -> (CharacteristicData, PeripheralName, CharacteristicId) -> Void' 
     // to expected argument type 'CharacteristicNotificationHandler?'
     private let badSupportedServices = [SupportedService(id: "2000", characteristics: badCharacteristics)]
     ////////
    // These declarations compile, presumably because handler1 is 
    // instantiated by the time this runs. But I don't want to do 
    // it this way...
    private var supportedCharacteristics: [SupportedCharacteristic] {
        get {
            return [SupportedCharacteristic(id: "1000", handler: handler1)]
        }
    }
    private var supportedServices: [SupportedService] {
        get {
            return [SupportedService(id: "2000", characteristics: supportedCharacteristics)]
        }
    }
    override init() {
        super.init()
        supportedServices[0].characteristics[0].handler?(NSData(), "one", "two")
    }
    private func handler1(value: CharacteristicData,
                          _ peripheralName: PeripheralName,
                          _ characteristicId: CharacteristicId) -> Void {
        print(#function)
    }
}

Answer 1

请注意，错误指出其给出的处理程序具有类型

(BleStuff) -> (CharacteristicData, PeripheralName, CharacteristicId) -> Void

不是(CharacteristicData, PeripheralName, CharacteristicId) -> Void

如果没有定义的实例，该方法就无法自行存在。

如果您的实例在此上下文中使用有意义，则可以将行更改为：

private let badCharacteristics = [SupportedCharacteristic.init(id: "1000", handler: handler1(aBLEStuffInstance)]

这起作用是因为方法是迅速中的咖喱功能。

这完全表明了不良设计。告诉我们您希望实现的目标是有益的。最有可能的是，handler1应该仅制成static。