JSONSerialization with URLSession。共享。dataTask错误

作为自学Swift的一部分,我正在开发一个天气应用程序。我目前正在尝试整合天气警报。我使用一个名为AlertData的结构来初始化API调用weather返回的数据。序列化API调用返回的数据后。或者,至少这是计划。我已经模仿了其他需要天气数据的课程。但要获得警报,我需要能够在数据任务中发送可变参数。我将苹果应用程序开发的URL扩展名与Swift一起使用(下面的代码),并将代码设置为使用用户当前位置发出参数,以获取用户当前所在位置的警报。

当我试图构造对weather的API调用时,我的问题来了。我的AlertDataController类中的gov(代码如下)。Xcode不断抛出不同的错误,我不知道为什么。我想在下面的代码中使用一个guard语句,但这会在显示的代码中引发一个错误“Cannot force unwrap value of non-optional type“[[String:Any]]”。当我在展开后将其设置为简单常量赋值时,它也会抛出相同的错误,因为扩展返回一个可选的URL。

当我直接从guard语句中的字符串构造URL时,相同的代码可以完美地工作,如中所示:

guard let url = URL(string: (baseURL + locationString + stations)) else {

我错过了什么?抛出错误的位置在dataTask内部,无论它是如何到达那里的,变量url都是一个未包装的url。提前谢谢。

控制器类别:

import Foundation
import CoreLocation

struct AlertDataController {

    func checkWxAlert(location: CLLocation, completion: @escaping (AlertData?) -> Void) {
        let baseURL = URL(string: "https://api.weather.gov/alert")!
        let locationString = "\(location.coordinate.latitude),\(location.coordinate.longitude)"
        var query = [
            "active": "1",
            "point": locationString
        ]

       guard let url = baseURL.withQueries(query) else {

            completion(nil)
            print("Unable to build URL in AlertDataController.checkWxAlert with supplied queries.")
            return
        }

        let task = URLSession.shared.dataTask(with: url) { (data, response, error) in

            if let data = data,
                let rawJSON = try? JSONSerialization.jsonObject(with: data),
                let json = rawJSON as? [String: Any],
                let featuresDict = json["features"] as? [[String: Any]],
                let propertiesArray = featuresDict!["properties"] as? [String: Any] {
Error: Cannot force unwrap value of non-optional type '[[String : Any]]'

                let alertData = AlertData(json: propertiesArray)
                completion(alertData)

            } else {
                print("Either no data was returned in AlertDataController.checkWxAlert, or data was not serialized.")

                completion(nil)
                return
            }
        }

        task.resume()
    }

}

URL扩展名:

import Foundation

extension URL {

    func withQueries(_ queries: [String: String]) -> URL? {
        var components = URLComponents(url: self, resolvingAgainstBaseURL: true)
        components?.queryItems = queries.flatMap { URLQueryItem(name: $0.0, value: $0.1) }
        return components?.url
    }

    func withHTTPS() -> URL? {
        var components = URLComponents(url: self, resolvingAgainstBaseURL: true)
        components?.scheme = "https"
        return components?.url
    }
}