無法用索引類型“字符串”下標“ [NSObject：AnyObject]”類型的值

Question

我在下面的代碼片段中遇到錯誤。 每當我嘗試構建它時，編譯器都會抱怨：

無法用索引類型“字符串”下標“ [NSObject：AnyObject]”類型的值

這是所有榮耀的代碼：

import Foundation
import MapKit

enum LocationKey: String {
    case Latitude = "lat"
    case Longitude = "long"
    case Title = "title"
}

extension MKPointAnnotation {
    var propertyState: [NSObject: AnyObject] {
        get {
            return [ LocationKey.Longitude.rawValue as NSObject: NSNumber(value: coordinate.latitude),
                     LocationKey.Longitude.rawValue as NSObject: NSNumber(value: coordinate.longitude),
                     LocationKey.Title.rawValue as NSObject: title as AnyObject]
        }
        set {
            let lat = (newValue[LocationKey.Latitude.rawValue] as NSNumber).doubleValue
            let long = (newValue[LocationKey.Longitude.rawValue] as NSNumber).doubleValue
            coordinate = CLLocationCoordinate2D(latitude: lat, longitude: long)
            title = newValue[LocationKey.Title.rawValue] as NSString
        }
    }
}

我真正遇到麻煩的代碼行是：

let lat = (newValue[LocationKey.Latitude.rawValue] as NSNumber).doubleValue
let long = (newValue[LocationKey.Longitude.rawValue] as NSNumber).doubleValue
title = newValue[LocationKey.Title.rawValue] as NSString

謝謝一群！

Answer 1

var propertyState: [NSObject: AnyObject]是一個字典，具有NSObject類型的鍵。 嘗試將其更改為String類型，看看是否可行。

Answer 2

這是因為您正在使用NSObject鍵創建一個Dictionary。

嘗試這個：

import Foundation
import MapKit

enum LocationKey: String {
    case Latitude = "lat"
    case Longitude = "long"
    case Title = "title"
}

extension MKPointAnnotation {
    var propertyState: [String: AnyObject] {
        get {
            return [ LocationKey.Longitude.rawValue: NSNumber(value: coordinate.latitude),
                     LocationKey.Longitude.rawValue: NSNumber(value: coordinate.longitude),
                     LocationKey.Title.rawValue: title as AnyObject]
        }
        set {
            guard let lat = (newValue[LocationKey.Latitude.rawValue] as? NSNumber)?.doubleValue,
                let long = (newValue[LocationKey.Longitude.rawValue] as? NSNumber)?.doubleValue else {
                return
            }
            coordinate = CLLocationCoordinate2D(latitude: lat, longitude: long)
            title = newValue[LocationKey.Title.rawValue] as? String
        }
    }
}

在代碼中，您已經在properyState setter中看到了按標准方式展開的可選內容，因為不使用強制展開是一種好習慣。

Answer 3

您的代碼太復雜了。 所有值都是值類型，因此將字典聲明為[String:Any] -可以解決該錯誤-並消除對NSNumber和AnyObject進行的所有丑陋類型轉換。

import Foundation
import MapKit

enum LocationKey: String {
    case latitude = "lat"
    case longitude = "long"
    case title = "title"
}


extension MKPointAnnotation {
    var propertyState: [String: Any] {
        get {
            return [ LocationKey.latitude.rawValue: coordinate.latitude,
                     LocationKey.longitude.rawValue: coordinate.longitude,
                     LocationKey.title.rawValue: title ?? ""]
        }
        set {
            guard let lat = newValue[LocationKey.latitude.rawValue] as? CLLocationDegrees,
            let long = newValue[LocationKey.longitude.rawValue] as? CLLocationDegrees else { return }
            coordinate = CLLocationCoordinate2D(latitude: lat, longitude: long)
            title = newValue[LocationKey.title.rawValue] as? String
        }
    }
}

您甚至可以將枚舉用作鍵

extension MKPointAnnotation {
    var propertyState: [LocationKey: Any] {
        get {
            return [ .latitude: coordinate.latitude,
                     .longitude: coordinate.longitude,
                     .title: title ?? ""]
        }
        set {
            guard let lat = newValue[.latitude] as? CLLocationDegrees,
            let long = newValue[.longitude] as? CLLocationDegrees else { return }
            coordinate = CLLocationCoordinate2D(latitude: lat, longitude: long)
            title = newValue[.title] as? String
        }
    }
}

注意：您的getter兩次使用LocationKey.Longitude ，這將導致編譯器錯誤。