Swift日历类为工作日返回错误的日期 [英] Swift Calendar class returning wrong date for weekday

问题描述

我对Swift 3中的Calendar类有疑问.

I have a question regarding the Calendar class in Swift 3:

基本上，我想获取下一个星期日的日期.但是，以下代码给了我错误的输出:

Basically, I wanted to get the Date of the next Sunday. However, the following code gives me the wrong output:

let cal = Calendar.current //gregorian
let today = Date(timeIntervalSinceNow: 0)
let date_c = DateComponents(calendar: cal, weekday: 1)

let today_weekday = cal.component(Calendar.Component.weekday, from: today)
let next_sunday = cal.nextDate(after: today, matching: date_c, matchingPolicy: Calendar.MatchingPolicy.nextTime)!

print(today_weekday) //prints out: 1 (today is Sunday, that's true)
print(next_sunday) //prints out: 2017-10-28 which is a Saturday

请注意，我昨天测试了代码，这就是为什么我写今天是星期日"的原因.我原本以为第二种主要产品是2017年10月29日(下一个星期日)，但是它给了我星期六.我在做什么错了?

Please note that I tested the code yesterday, that's why I wrote "today is Sunday". I was expecting the second print output to be the 2017-10-29 (next Sunday) however, it is giving me Saturday. What am I doing wrong?

推荐答案

日期始终按照格林尼治标准时间(GMT)时区打印.

Dates are always printed as if they are in the GMT timezone.

假设您的时区为UTC + 1，那么下一个星期日将为您所在时区的 29-10-2017 00:00:00 .但是，此 Date 实例在GMT中表示为 28-10-2017 23:00:00 .

Suppose your time zone is UTC+1, then next Sunday will be 29-10-2017 00:00:00 in your time zone. However, this Date instance is expressed as 28-10-2017 23:00:00 in GMT.

因此 nextDate 确实返回正确的日期，只是未在您的时区中格式化.要解决此问题，只需使用 DateFormatter :

So nextDate does return the correct date, it's just not formatted in your time zone. To fix this, just use a DateFormatter:

let formatter = DateFormatter()
formatter.dateStyle = .short
print(formatter.string(from: next_sunday))

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