/// DateTools.swift
 
import Foundation
 
extension Date {
    func daysBetweenDate(toDate: Date) -> Int {
        let components = Calendar.current.dateComponents([.day],from: self,to: toDate) return components.day ?? 0 } } 

/// xxxController.swift
 
 let formatter = DateFormatter()
 formatter.dateFormat = "YYYYMMdd"
 let endDate = formatter.date(from: "20181220")
 
 /// 当前日期 - 考试日期
 let date = Date()
 let days = Date().daysBetweenDate(toDate: endDate!)
 print("相差天数为 ==",days)