TL; DR:一个JSON请求有时返回一个对象,有时返回一个键的对象数组,但我不知道如何使用Swift 4正确解析该对象。
前言:我正在使用NextBus API开发一个公交服务应用程序,以为Chapel Hill地区的公交车时刻表提供更新和预测。但是,在获取公交车站的预测信息时(在NextBus API PDF第13-15页上的预测请求信息),我遇到了一个问题。
问题:
停止预测的请求将返回两个键:“预测”和“版权”。尽管“版权”键始终返回预测请求的字符串,但“预测”键有时会返回对象,有时会根据路线上是否有两辆公交车返回数组。
这是邮递员可视化的问题:
预测返回一个数组:
{
"predictions": [
{
"agencyTitle": "Chapel Hill Transit",
"routeTag": "N",
"routeTitle": "N",
"stopTitle": "Estes Park Apts - Departure",
"stopTag": "estepark",
"dirTitleBecauseNoPredictions": "To Family Practice Building"
},
{
"agencyTitle": "Chapel Hill Transit",
"routeTag": "N",
"routeTitle": "N",
"stopTitle": "Estes Park Apts - Arrival",
"stopTag": "estepark_a",
"dirTitleBecauseNoPredictions": "To Family Practice Building"
}
],
"copyright": "All data copyright Chapel Hill Transit 2018."
}
预测返回一个对象:
{
"predictions": {
"agencyTitle": "Chapel Hill Transit",
"routeTag": "A",
"routeTitle": "A",
"stopTitle": "Martin Luther King Jr Blvd at Timber Hollow",
"stopTag": "airptimb_s",
"dirTitleBecauseNoPredictions": "To Northside"
},
"copyright": "All data copyright Chapel Hill Transit 2018."
}
我正在使用Swift 4在Xcode 9.4.1中创建此应用程序。这是我当前处理请求的代码:
func fetchStopPrediction(stopId: String, routeTag: String, completion: @escaping (Predictions) -> Void) {
let routeInfo = "\(stopId)&routeTag=\(routeTag)"
let urlString = baseUrl + routeInfo
print(urlString)
Alamofire.request(urlString, method: .get).responseJSON { (response) in
if let jsonResponse = response.result.value {
print("JSON: \(jsonResponse)")
}
if let data = response.data {
do {
let predictions = try self.decoder.decode(Predictions.self, from: data)
completion(predictions)
} catch let error {
print("Error", error)
}
}
}
}
struct Predictions: Codable {
let predictions: [Prediction?]
let copyright: String?
}
答案 0 :(得分:1)
您必须编写一个自定义初始化程序。首先解码字典,如果字典解码失败,则失败
struct Predictions : Decodable {
let predictions: [Prediction]
let copyright: String
private enum CodingKeys: String, CodingKey { case predictions, copyright }
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
copyright = try container.decode(String.self, forKey: .copyright)
do {
let prediction = try container.decode(Prediction.self, forKey: .predictions)
predictions = [prediction]
} catch DecodingError.typeMismatch {
predictions = try container.decode([Prediction].self, forKey: .predictions)
}
}
}