尝试访问字典时出现 Swift 错误：`找不到成员'下标'`

Question

这不会编译： 我尝试了几种不同的方法；声明字典的不同方式，更改其类型以匹配数据的嵌套。我还尝试明确说我的Any 是一个集合，因此它可以下标。没有骰子。

import UIKit


import Foundation

class CurrencyManager {

    var response = Dictionary<String,Any>()
    var symbols = []


    struct Static {
        static var token : dispatch_once_t = 0
        static var instance : CurrencyManager?
    }

    class var shared: CurrencyManager {
        dispatch_once(&Static.token) {  Static.instance = CurrencyManager() }
        return Static.instance!
    }

    init(){
        assert(Static.instance == nil, "Singleton already initialized!")
        getRates()

    }


    func defaultCurrency() -> String {

        let countryCode  = NSLocale.currentLocale().objectForKey(NSLocaleCountryCode) as String
        let codesToCountries :Dictionary = [ "US":"USD" ]

        if let localCurrency = codesToCountries[countryCode]{
            return localCurrency
        }

        return "USD"

    }

    func updateBadgeCurrency() {

        let chanCurr = defaultCurrency()

        var currVal :Float = valueForCurrency(chanCurr, exchange: "Coinbase")!

        UIApplication.sharedApplication().applicationIconBadgeNumber = Int(currVal)

    }

    func getRates() {
        //Network code here
        valueForCurrency("", exchange: "")
    }

    func valueForCurrency(currency :String, exchange :String) -> Float? {
        return response["current_rates"][exchange][currency] as Float
    }


}

Answer 1

我们来看看

response["current_rates"][exchange][currency]

response 被声明为Dictionary<String,Any>()，因此在第一个下标之后，您尝试在 Any 类型的对象上调用另外两个下标。

解决方案 1. 将响应类型更改为嵌套字典。请注意，我添加了问号，因为每当您访问字典项目时，您都会得到一个可选的。

var response = Dictionary<String,Dictionary<String,Dictionary<String, Float>>>()

func valueForCurrency(currency :String, exchange :String) -> Float? {
    return response["current_rates"]?[exchange]?[currency]
}

解决方案 2. 在解析时将每个级别转换为字典。确保仍然检查可选值是否存在。

var response = Dictionary<String,Any>()

func valueForCurrency(currency :String, exchange :String) -> Float? {
    let exchanges = response["current_rates"] as? Dictionary<String,Any>

    let currencies = exchanges?[exchange] as? Dictionary<String,Any>

    return currencies?[currency] as? Float
}

Answer 2

您可以按照以下步骤获取嵌套字典数据：

let imageData: NSDictionary = userInfo["picture"]?["data"]? as NSDictionary
let profilePic = imageData["url"] as? String

Answer 3

func valueForCurrency(currency :String, exchange :String) -> Float? {
    if let exchanges = response["current_rates"] as? Dictionary<String,Any> {
        if let currencies = exchanges[exchange] as? Dictionary<String,Any> {
            return currencies[currency] as? Float
        }
    }
    return nil
}

Answer 4

response 是这样声明的：

var response = Dictionary<String,Any>()

因此编译器认为response["current_rates"] 将返回Any。这可能是也可能不是可下标索引的东西。

您应该能够使用嵌套字典定义您的类型，3 个级别，最终您会得到一个浮点数。您还需要使用可选链接进行深入研究，因为字典可能有也可能没有该键的值，因此它的下标访问器返回一个可选的。

var response = Dictionary<String,Dictionary<String,Dictionary<String,Float>>>()
// ... populate dictionaries
println(response["current_rates"]?["a"]?["b"]) // The float