json - Swift .flatMap 未将 json 数据初始化为结构

Question

我下载了一个 JSON 文件，我正在尝试将 .flatMap 转换为我创建的结构数组，但 .flatMap 并未将数据初始化到结构中。

下面是 JSON 文件的解析版本，它代表数组中的一个结构:

[["eventUri": <null>, 
"wgt": 266482320, 
"source": {
    dataType = news;
    title = WAFB;
    uri = "wafb.com";
}, 
"uri": 885629090, 
"body": A bunch of text, 
"lang": eng, 
"dateTime": 2018-06-12T06:52:00Z, 
"date": 2018-06-12, 
"sim": 0, 
"isDuplicate": 1, 
"title": Now a candidate, Romney appears to embrace Trump presidency,
"time": 06:52:00, 
"url": http://www.wafb.com/story/38391905/now-a-candidate-romney-appears-to-embrace-trump-presidency, 
"dataType": news]]

这是结构体，带有结构体的共享实例，以及 flatMap 方法。所有初始化器下标均根据 JSON 的键命名:

struct Article {

    static var sharedInstance: [Article] = [Article]()

    // MARK: Properties

    var dataType = ""
    var date = ""
    var eventUri = ""
    var isDuplicate = false
    var sourceName = ""
    var lang = ""
    var sim = 0.0
    var time = ""
    var articleTitle = ""
    var image: UIImage? = nil

    // MARK: Initializer
    init?(dictionary: [String:AnyObject]) {

        // GUARD: Do all dictionaries have values?
        guard
            let dataType = dictionary[EventRegistry.ParameterValues.dataType] as? String,
            let date = dictionary[EventRegistry.ParameterValues.date] as? String,
            let eventUri = dictionary[EventRegistry.ParameterValues.eventUri] as? String,
            let isDuplicate = dictionary[EventRegistry.ParameterValues.isDuplicate] as? Bool,
            let source = dictionary[EventRegistry.ParameterKeys.source] as? [String:Any],
            let sourceName = source[EventRegistry.ParameterValues.sourceName] as? String,
            let lang = dictionary[EventRegistry.ParameterValues.lang] as? String,
            let sim = dictionary[EventRegistry.ParameterValues.sim] as? Double,
            let time = dictionary[EventRegistry.ParameterValues.time] as? String,
            let articleTitle = dictionary[EventRegistry.ParameterValues.articleTitle] as? String

            // If not, return nil
            else { return nil }

        // Otherwise, initialize values
        self.dataType = dataType
        self.date = date
        self.eventUri = eventUri
        self.isDuplicate = isDuplicate
        self.sourceName = sourceName
        self.lang = lang
        self.sim = sim
        self.time = time
        self.articleTitle = articleTitle
    }

    static func articlesFromResults(_ results: [[String:AnyObject]]) -> [Article] {

        return results.flatMap(Article.init)
    }

}

这是我对启动 flatMap 方法的调用，该方法不返回结果:

func getEventRegistrySearchResults(completionHandlerForSearchResults: @escaping (_ articles: [Article]?, _ errorString: String?) -> Void) {

taskForGetEventRegistrySearchResults(method: "", parameters: ["" : (Any).self]) { (result, error) in

    if error != nil {
        print("There was an error getting articles")
    }

    if let result = result {

        if let articles = result["articles"] as? [String:AnyObject] {

            if let articleResults = articles["results"] as? [[String:AnyObject]] {
                Article.sharedInstance = Article.articlesFromResults(articleResults)
                print(Article.sharedInstance.count) // Returns 0
                }
            } else {
                completionHandlerForSearchResults(nil, "There was a problem")
            }
        }
    }
}

在此处打印“articleResults”会为我提供上面的 JSON 文件，但是当我尝试将其 .flatMap 到我的结构数组中时，它不会初始化其中任何一个。我错过了什么？

Answer 1

如果我是你，我会在我的 Article 结构中实现 Swift 4 Codable 协议(protocol)，然后使用 JSONDecoder 解码数组，如下所示

let decoder = JSONDecoder()
let articles = try! decoder.decode(Array<Article.self>, for: results)

所以你的文章结构将如下所示:

struct Article: Codable {
    var dataType: String
    var date: Date
    var eventUri: URL
    var isDuplicate: Bool
    var sourceName: String
    var lang: String
    var sim: Double
    var time: String
    var articleTitle: String
    var image: UIImage? = nil

    static func articlesFromResults(_ results: [[String : Any]]) -> [Article] {
        let decoder = JSONDecoder()
        let articles = try! decoder.decode(Array<Article.self>, for: results)
    }
}

现在，这留下了图像属性的问题，因为 UIImage 不符合 Codable，但您可以在此处查找解决方案 How to conform UIImage to Codable?