问如何使用SwiftyJSON框架读取本地声明的JSON

EN

import Foundation
import SwiftyJSON
let mockShifts = "{\"numOfShiftsInDay\": 3,\"shifts\": [{\"StartTime\": \"06:30\",\"EndTime\": \"14:00\"},{\"StartTime\": \"14:00\",\"EndTime\": \"19:00},{\"StartTime\": \"19:00\",\"EndTime\":\"01:00\"}]}"
class WeeklySchedule {

var shifts: [Shift] = []
var shiftsAmount: Int = 3
var relative: Int = 0
func setShiftsAmount(amount: Int){
    self.shiftsAmount = amount
    for _ in 1...amount{
        self.shifts.append(Shift())
    }
    getShifts()
}

func getRelative() -> Int{
    return relative
}
func getShifts(){
    let data = mockShifts.data(using: .utf8)!
    let json = JSON(data: data)
    print(mockShifts) //This prints out a JSON that looks OK to me
    print(json)       //This prints NULL
    if let numOfShifts = json["numOfShiftsInDay"].string {
        print(numOfShifts) //This code is unreachable
    }
}
}