属性声明

Question

我想静态地“配置”一个与BLE相关的类，其中包含支持的服务，特性，通知处理程序等，带有typealiases和结构，有点像下面的类。但是，在声明引用该方法的let常量属性时，Swift编译器不喜欢我引用实例方法的方式（参见badCharacteristics）。做一些与此类似的好方法是什么？必须有一种更加快速兼容的方式来引用实例方法来实现相同的目标。

我考虑过创建一个更加简化的示例，但我认为一个更现实的例子可能会带来更多好处。

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

以下是代码：

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，错误表明给定的处理程序具有类型

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

不是(CharacteristicData, PeripheralName, CharacteristicId) -> Void

该方法不能单独存在而没有定义的实例来调用它。

如果您有一个在此上下文中使用的实例，则可以将您的行更改为：

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

这是因为methods are curried functions in Swift。

然而，这很好地表明了糟糕的设计。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static。