URLComponentsExtension.swift

import UIKit
/*
 Extension with queryItems to Dictionary and  Dictionary to queryItems
 */
extension URLComponents {
    
    /*
     Get the dictionary from queryItems
     */
    var queryItemsAsDictionary: [String:String?]? {
        guard let queryItems = queryItems else {
            return nil
        }
        var dict:[String:String?] = [:]
        for item in queryItems {
            dict[item.name] = item.value
        }
        return dict
    }
    /*
     Replace the queryItems from items in dictionary
     */
    mutating func replaceQueryItems(fromDictionary dictionary:[String:String?]?) {
        guard let dictionary = dictionary, dictionary.count > 0 else {
            queryItems = nil
            return
        }
        var newQueries:[URLQueryItem]? = nil
        for (name,value) in dictionary {
            if newQueries == nil { newQueries = [] }
            let queryItem = URLQueryItem(name: name, value: value)
            newQueries?.append(queryItem)
        }
        queryItems = newQueries
    }
}

var components = URLComponents(string: "htttps://www.server/somepath/anotherpath?keyA=valueA,keyB=valueB")
print(components?.url ?? "NIL")
var queryDictionary = components?.queryItemsAsDictionary

queryDictionary?["keyC"] = "valueC"
components?.replaceQueryItems(fromDictionary: queryDictionary)

print(components?.url ?? "NIL")