比较两个日期以在 Swift 4 中更新数据库

Question

我有这个代码：

func getSystemDate()-> String{
        let date = Date()
        let calendar = Calendar.current
        let hour = String(format: "%02d",calendar.component(.hour, from: date))
        let minutes = String(format: "%02d",calendar.component(.minute, from: date))
        let seconds = String(format: "%02d",calendar.component(.second, from: date))

        let day = String(format: "%02d",calendar.component(.day, from: date))
        let month = String(format: "%02d",calendar.component(.month, from: date))
        let year = String(format: "%02d",calendar.component(.year, from: date))

        let fullDate = "\(year)-\(month)-\(day) \(hour):\(minutes):\(seconds)"

        return fullDate
    }
let date1 = getSystemDate()
let date2 = "2018-05-23 13:14:47"

if date1 > date2 {
    print("its ok - update available")
} else {
    print("wrong - you have actually database")
}

我的函数getSystemDate() 以字符串形式返回实际日期。 在变量date2 - 我有数据库更新日期。

我需要确定是否可以更新数据库并将当前日期与可用数据库的日期进行比较：...

如何比较这些日期？

Answer 1

您可以使用Calendar 比较两个Dates。你也可以去second unit，如果差值为0表示它们相等，否则你可以检查哪个更大：

let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
//dateFormatter.timeZone   = TimeZone(abbreviation: "UTC")  // To add timezone

guard let dateOne = dateFormatter.date(from: "2018-05-23 13:14:47"), let dateTwo = dateFormatter.date(from: "2018-05-23 14:14:47") else {
    print("One of the date conversion is nil")
    return
}

print(dateOne, dateTwo)

let components = Calendar.current.dateComponents([.second], from: dateOne, to: dateTwo)
let secondsInBetween: Int = components.second!

print(secondsInBetween)