如何在 object 的數組中解碼嵌套的 JSON object？

Question

我需要在嵌套的 JSON 深處檢索數據，但這樣做有很多麻煩。 有問題的文件可以在https://waterservices.usgs.gov/nwis/iv/?format=json&indent=on&sites=08155200&parameterCd=00065&siteStatus=all 找到。

// MARK: - Post
struct Post: Codable {
    let name, declaredType, scope: String?
    let value: PostValue?
    let postNil, globalScope, typeSubstituted: Bool?

    enum CodingKeys: String, CodingKey {
        case name, declaredType, scope, value
        case postNil
        case globalScope, typeSubstituted
    }
}

// MARK: - PostValue
struct PostValue: Codable {
    let queryInfo: QueryInfo?
    let timeSeries: [TimeSery]?
}

// MARK: - QueryInfo
struct QueryInfo: Codable {
    let queryURL: String?
    let criteria: Criteria?
    let note: [Note]?
}

// MARK: - Criteria
struct Criteria: Codable {
    let locationParam, variableParam: String?
    let parameter: [JSONAny]?
}

// MARK: - Note
struct Note: Codable {
    let value, title: String?
}

// MARK: - TimeSery
struct TimeSery: Codable {
    let sourceInfo: SourceInfo?
//    let variable: Variable?
//    let values: [TimeSeryValue]?
    let name: String?
}

// MARK: - SourceInfo
struct SourceInfo: Codable {
    let siteName: String?
//    let siteCode: [SiteCode]?
//    let timeZoneInfo: TimeZoneInfo?
    let geoLocation: GeoLocation?
    let note, siteType: [JSONAny]?
//    let siteProperty: [SiteProperty]?
}

// MARK: - GeoLocation
struct GeoLocation: Codable {
    let geogLocation: GeogLocation?
    let localSiteXY: [JSONAny]?
}

// MARK: - GeogLocation
struct GeogLocation: Codable {
    let srs: String?
    let latitude, longitude: Double?
}

檢索數據的代碼：

URLSession.shared.dataTask(with: url) { data, _, _ in
    if let data = data {
        let posts = try! JSONDecoder().decode(Post.self, from: data)
        if let coord = (posts.value?.timeSeries?.sourceInfo?.geoLocation?.geogLocation?.srs) {
            print(coord)
        }
    }
}.resume()

不幸的是，這會返回錯誤

error: ParseJSON.playground:330:89: error: type of expression is ambiguous without more context

Answer 1

timeSeries被定義為[TimeSery] ，這意味着它是一個數組，但您試圖訪問它，就好像它只是一個值一樣。 由於我不確定您的意圖是什么，因此很難說確切的修復方法是什么，但一種可能性是從中訪問第first值（相當於要求[0] ，但它返回一個 Optional）：

posts.value?.timeSeries?.first?.sourceInfo?.geoLocation?.geogLocation?.srs

---

順便說一句，調試此問題的一種方法是將表達式分解為不太復雜的部分（我從posts.value開始，然后添加代碼直到找到問題（在本例中為timeSeries.sourceInfo ）