比较两个日期以获取组件答案

【问题标题】：Comparing two dates for getting components比较两个日期以获取组件
【发布时间】：2020-11-16 17:56:18
【问题描述】：

我正在比较两个日期，当我们在同一个月执行操作时，它可以完美运行，但是当月份较高时，即 8 月 8 日，日期较低，假设 2，当前日期为 27，而 mont 为 7 月 7 日，所以对于这个比较我得到了错误的负值。

这是我的功能：

func countDonwn(isStumpStarted: Bool = false)-> String? {
    let date = Date()
    
    let calendar = Calendar.current
    let components = calendar.dateComponents([.hour, .minute, .second, .day], from: date as Date)
    let currentDate = calendar.date(from: components)?.toLocalTime()
    let userCalendar = Calendar.current
    guard let endDte = (self.getDate(defaultFormat: "yyyy-MM-dd'T'HH:mm:ss.SSSZ")) else {return nil }
    let competitionDate = calendar.dateComponents([.hour, .minute, .second, .day], from: endDte as Date)
    if endDte < (date as Date) {
        return ""
    }
    
    let competitionDay = userCalendar.date(from: competitionDate as DateComponents)!.toLocalTime()
    let CompetitionDayDifference = calendar.dateComponents([.day, .hour, .minute, .second], from: currentDate!, to: competitionDay)
    let daysLeft = CompetitionDayDifference.day
    let hoursLeft = CompetitionDayDifference.hour
    let minutesLeft = CompetitionDayDifference.minute
    let secondLeft = CompetitionDayDifference.second
    if daysLeft != 0 && !isStumpStarted {
        return "\(String(describing: daysLeft ?? 0))d \(String(format: "%02d", hoursLeft ?? 0)):\(String(format: "%02d", minutesLeft ?? 0)):\(String(format: "%02d", secondLeft ?? 0))"
        
    } else if daysLeft == 0 && hoursLeft == 0 && minutesLeft == 0 && secondLeft == 0 {
        return ""
    }
    
    return "\(String(format: "%02d", hoursLeft ?? 0)):\(String(format: "%02d", minutesLeft ?? 0)):\(String(format: "%02d", secondLeft ?? 0))"
}

【问题讨论】：

标签： ios swift date nsdatecomponents

【解决方案1】：

可以使用 Calendar 函数和 DateComponents 执行日期比较

let calendar = Calendar.current
let delta = calendar.dateComponents([.hour, .minute, .second], 
                                    from: date, 
                                    to: endDte)

print("\(String(format: "%02d", delta.hour!)):\(String(format: "%02d", delta.minute!)):\(String(format: "%02d", delta.second!))")

所以我认为你的功能可以缩短为

func countDonwn(isStumpStarted: Bool = false)-> String? {
    let date = Date()

    guard let endDte = (self.getDate(defaultFormat: "yyyy-MM-dd'T'HH:mm:ss.SSSZ")),
    date.compare(endDte) == .orderedAscending else {
        return nil
    }

    let calendar = Calendar.current
    let delta = calendar.dateComponents([.hour, .minute, .second], from: fromDate, to: toDate)

    return "\(String(format: "%02d", delta.hour!)):\(String(format: "%02d", delta.minute!)):\(String(format: "%02d", delta.second!))"
}

请注意，在调用 calendar.dateComponents(_ ,from:, to:) 函数时，可以强制解开 delta 的日期组件

【讨论】：