Question

我在下面的代码片段中遇到错误。每次我尝试构建它时，编译器都会抱怨：

无法下标类型＆＃39; [NSObject：AnyObject]＆＃39;索引类型为＆＃39; String＆＃39;

这是代码中的所有荣耀：

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
        }
    }
}

我真正遇到麻烦的代码行是：

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

非常感谢！

Answer 1

var propertyState: [NSObject: AnyObject]是一个包含NSObject类型键的词典。尝试将其更改为键入String并查看是否有效。

Answer 2

这是因为你正在用NSObject键创建一个词典。

试试这个：

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
        }
    }
}

在代码中，您在properyState setter中看到了сonditionally unwrapped个选项，因为不使用强制解包是一种不错的做法。

Answer 3

您的代码太复杂了。所有值都是值类型，因此将字典声明为[String:Any] - 这样可以解决错误 - 并将所有丑陋的类型转换为NSNumber和AnyObject。

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
        }
    }
}

您甚至可以将枚举用作键

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使用LocationKey.Longitude两次，这将导致编译器错误。

不能下标类型＆＃39; [NSObject：AnyObject]＆＃39;索引类型＆＃39;字符串＆＃39;

3 个答案: