如何访问 JSON API 中的整数值？

Question

我正在尝试快速从 JSON 文件中检索整数值。我这样做如下：self.trip.dist = String(decodedJson.Trip[self.tripIndex].LegList.Leg[i].dist) 但我收到此错误error。

这是我正在访问的JSON file 的链接。我正在尝试访问 dist 值。

这些是我的结构：

struct JSONStructure: Decodable {
    var Trip: [TripStructure]
}
 
struct TripStructure: Decodable {
    var LegList: LegListStructure
}
 
struct LegListStructure: Decodable {
    var Leg: [LegStructure]
}
 
struct LegStructure: Decodable {
    var Origin: StationStructure
    var Destination: StationStructure
    var Product: ProductStructure
    var name: String
    var type: String
    var dist: Int
}
 
struct StationStructure: Decodable {
    var time: String
    var name: String
    var date: String
}
 
struct ProductStructure: Decodable {
    var catIn: String
}
 
 
// Just to condense my varibales
struct LocationInfo {
    var iD = String()
    var input = String()
    var lat = String()
    var lon = String()
    var name = String()
    var time = String()
    var date = String()
    var vehicleType = String()
    var transportType = String()
    var dist = String()
    var legName = String()
}

这是我用来调用函数的函数：

    @Published var trip: LocationInfo = LocationInfo()
    @Published var dest: LocationInfo = LocationInfo()
    @Published var origin: LocationInfo = LocationInfo()
    @Published var arrivalTime = String()
    @Published var travelDate = String()
    @Published var searchForArrival = String()
    @Published var tripIndex = Int()
    @Published var Trips: [Dictionary<String, String>] = []
 
public func FetchTrip() {
        Trips.removeAll()
        
        let tripKey = "40892db48b394d3a86b2439f9f3800fd"
        let tripUrl = URL(string: "http://api.sl.se/api2/TravelplannerV3_1/trip.json?key=\(tripKey)&originExtId=\(self.origin.iD)&destExtId=\(self.dest.iD)&Date=\(self.travelDate)&Time=\(self.arrivalTime)&searchForArrival=\(self.searchForArrival)")
        
        URLSession.shared.dataTask(with: tripUrl!) {data, response, error in
            if let data = data {
                do {
                    let decodedJson = try JSONDecoder().decode(JSONStructure.self, from: data)
                    self.tripIndex = decodedJson.Trip.count - 1
                    
                    for i in 0..<decodedJson.Trip[self.tripIndex].LegList.Leg.count {
                        self.trip.transportType = decodedJson.Trip[self.tripIndex].LegList.Leg[i].type
 
                        if self.trip.transportType == "WALK" {
                            self.origin.name = decodedJson.Trip[self.tripIndex].LegList.Leg[i].Origin.name
                            self.origin.time = String(decodedJson.Trip[self.tripIndex].LegList.Leg[i].Origin.time.prefix(5))
                            self.origin.date = decodedJson.Trip[self.tripIndex].LegList.Leg[i].Origin.date
 
                            self.dest.name = decodedJson.Trip[self.tripIndex].LegList.Leg[i].Destination.name
                            self.dest.time = String(decodedJson.Trip[self.tripIndex].LegList.Leg[i].Destination.time.prefix(5))
                            self.dest.date = decodedJson.Trip[self.tripIndex].LegList.Leg[i].Destination.date
                            
                            self.trip.vehicleType = decodedJson.Trip[self.tripIndex].LegList.Leg[i].Product.catIn
                            self.trip.dist = String(decodedJson.Trip[self.tripIndex].LegList.Leg[i].dist) // This is where the problem lies
                            
                            self.Trips.append(["Origin": self.origin.name, "Destination": self.dest.name, "OriginTime": self.origin.time, "DestTime": self.dest.time, "OriginDate": self.origin.date, "DestDate": self.dest.date, "TransportType": self.trip.transportType, "VehicleType": self.trip.vehicleType, "Distance": self.trip.dist])
                        }
                        
                        else {
                            self.origin.name = decodedJson.Trip[self.tripIndex].LegList.Leg[i].Origin.name
                            self.origin.time = String(decodedJson.Trip[self.tripIndex].LegList.Leg[i].Origin.time.prefix(5))
                            self.origin.date = decodedJson.Trip[self.tripIndex].LegList.Leg[i].Origin.date
 
                            self.dest.name = decodedJson.Trip[self.tripIndex].LegList.Leg[i].Destination.name
                            self.dest.time = String(decodedJson.Trip[self.tripIndex].LegList.Leg[i].Destination.time.prefix(5))
                            self.dest.date = decodedJson.Trip[self.tripIndex].LegList.Leg[i].Destination.date
                            
                            self.trip.vehicleType = decodedJson.Trip[self.tripIndex].LegList.Leg[i].Product.catIn
                            self.trip.legName = decodedJson.Trip[self.tripIndex].LegList.Leg[i].name
                            
                            self.Trips.append(["Origin": self.origin.name, "Destination": self.dest.name, "OriginTime": self.origin.time, "DestTime": self.dest.time, "OriginDate": self.origin.date, "DestDate": self.dest.date, "TransportType": self.trip.transportType, "VehicleType": self.trip.vehicleType, "LegName": self.trip.legName])
                        }
                    }
                } catch {
                    print(error)
                }
            }
        }.resume()
    }

我在控制台中收到此错误： keyNotFound(CodingKeys(stringValue: "dist", intValue: nil), Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "Trip", intValue: nil), _JSONKey(stringValue: "Index 0", intValue: 0), CodingKeys(stringValue: "LegList", intValue: nil), CodingKeys(stringValue: "Leg", intValue: nil), _JSONKey(stringValue: "Index 0", intValue: 0)], debugDescription: "No value associated with key CodingKeys(stringValue: \"dist\", intValue: nil) (\"dist\").", underlyingError: nil))

Answer 1

这个网站很棒：https://app.quicktype.io您只需粘贴您的 json，它就会为您编写 Codable。 QED。

您需要使用 Optional Int 来提取 dist 值，因为并非所有腿都有一个。

这是访问dist 值所需的最低要求：

func example() {
    let url = URL(string: "https://api.sl.se/api2/TravelplannerV3_1/trip.json?key=40892db48b394d3a86b2439f9f3800fd&originExtId=300101416&destExtId=300101426&Date=2021-04-15&Time=08:00&searchForArrival=1")!
    URLSession.shared.dataTask(with: url) { (data, response, error) in
        if let data = data {
            let travelplanner = try? JSONDecoder().decode(Travelplanner.self, from: data)
            print(travelplanner as Any)
        }
    }
    .resume()
}

struct Travelplanner: Codable {
    let trip: [Trip]

    enum CodingKeys: String, CodingKey {
        case trip = "Trip"
    }
}

struct Trip: Codable {
    let legList: LegList

    enum CodingKeys: String, CodingKey {
        case legList = "LegList"
    }
}

struct LegList: Codable {
    let leg: [Leg]

    enum CodingKeys: String, CodingKey {
        case leg = "Leg"
    }
}

struct Leg: Codable {
    let origin: Station
    let destination: Station
    let product: Product?
    let name: String
    let type: String
    let dist: Int?

    enum CodingKeys: String, CodingKey {
        case origin = "Origin"
        case destination = "Destination"
        case product = "Product"
        case name
        case type
        case dist
    }
}

struct Station: Codable {
    let name: String
    let time: String
    let date: String
}

struct Product: Codable {
    let catIn: String
}

Answer 2

很高兴您找到了解决方案。我认为您的代码还有其他问题需要解决。

以下代码具有相同的效果，但 IMO 更简洁：

    func fetchTrip() {
        let url = URL(string: "https://api.sl.se/api2/TravelplannerV3_1/trip.json?key=40892db48b394d3a86b2439f9f3800fd&originExtId=300101416&destExtId=300101426&Date=2021-04-15&Time=08:00&searchForArrival=1")!
        URLSession.shared.dataTask(with: url) { (data, response, error) in
            if let data = data {
                let decodedJson = try! JSONDecoder().decode(Travelplanner.self, from: data)
                let lastLeg = decodedJson.trip.last?.legList.leg.last
                self.tripIndex = decodedJson.trip.count - 1
                self.trip.transportType = lastLeg?.type ?? ""
                self.origin.name = lastLeg?.origin.name ?? ""
                self.origin.time = lastLeg.map { String($0.origin.time.prefix(5)) } ?? ""
                self.origin.date = lastLeg?.origin.date ?? ""
                self.dest.name = lastLeg?.destination.name ?? ""
                self.dest.time = lastLeg.map { String($0.destination.time.prefix(5)) } ?? ""
                self.dest.date = lastLeg?.destination.date ?? ""
                self.trip.vehicleType = lastLeg?.product?.catIn ?? ""
                if let lastWalkLeg = decodedJson.trip.last?.legList.leg.last(where: { $0.type == "WALK" }) {
                    self.trip.dist = String(lastWalkLeg.dist ?? 0)
                }
                if let lastNonwalkLeg = decodedJson.trip.last?.legList.leg.last(where: { $0.type != "WALK" }) {
                    self.trip.legName = lastNonwalkLeg.name
                }

                self.trips = (decodedJson.trip.last?.legList.leg ?? [])
                    .map { $0.asDict }
            }
        }
        .resume()
    }
}

extension Leg {
    var asDict: [String: String] {
        [
            "Origin": origin.name,
            "Destination": destination.name,
            "OriginTime": String(origin.time.prefix(5)),
            "DestTime": String(destination.time.prefix(5)),
            "OriginDate": origin.date,
            "DestDate": destination.date,
            "TransportType": type,
            "VehicleType": product?.catIn ?? "",
        ].merging(type == "WALK" ? ["Distance": String(dist ?? 0)] : ["LegName": name], uniquingKeysWith: { $1 })
    }
}

对于大多数变量，您每次都通过循环分配给相同的 var。这只是浪费。从循环的最后一个元素中分配值并完成它。

if...else... 块中完成的大部分工作都是相同的。将相同的部分分开，只将关心Leg.type 的部分放在 if/else 块中。您实际上是在类的其他方法中使用所有类属性，还是只是使用它们以一种奇怪的方式制作局部变量？ （我在上面的代码中假设前者以防万一。）如果您不需要在其他方法中需要所有其他属性，唯一的一点是填充trips数组，您可以卸载大部分代码（当然self.trips =... 行除外。