Swift3 iOS开发：如何通过Calendar获取上周日期？

嘿，你已经成功实现本周日期的获取了，这一步做得很好！要获取上周的日期，只需要在你现有代码的基础上稍作调整，核心思路是先拿到上周的基准日期，再用同样的逻辑计算该周的所有日期。

修改后的完整代码 #

let dateInWeek = Date()
let calendar = Calendar.current

// 先获取上周的基准日期（当前日期减去7天）
guard let lastWeekDate = calendar.date(byAdding: .day, value: -7, to: dateInWeek) else {
    fatalError("Failed to get last week date")
}

// 用上周的日期来计算周范围和日期数组
let dayOfWeek = calendar.component(.weekday, from: lastWeekDate)
let weekdays = calendar.range(of: .weekday, in: .weekOfYear, for: lastWeekDate)!
let lastWeekDates = (weekdays.lowerBound ..< weekdays.upperBound)
    .flatMap { calendar.date(byAdding: .day, value: $0 - dayOfWeek, to: lastWeekDate) }

print(lastWeekDates)

关键修改说明 #

• 新增lastWeekDate：通过calendar.date(byAdding: .day, value: -7, to: dateInWeek)获取当前日期往前推7天的日期，这就是上周对应今天的日期。
• 后续计算dayOfWeek、weekdays以及生成日期数组时，全部用lastWeekDate替代原来的dateInWeek，这样就能得到上周完整的7天日期了。

根据你提供的本周日期示例（2018-05-13至2018-05-19），修改后的代码输出应该是：

[2018-05-06 07:12:44 +0000, 2018-05-07 07:12:44 +0000, 2018-05-08 07:12:44 +0000, 2018-05-09 07:12:44 +0000, 2018-05-10 07:12:44 +0000, 2018-05-11 07:12:44 +0000, 2018-05-12 07:12:44 +0000]

可选：封装成可复用函数 #

为了方便后续复用，你可以把获取某一周日期的逻辑封装成扩展函数：

extension Calendar {
    func datesOfWeek(for date: Date) -> [Date] {
        let dayOfWeek = component(.weekday, from: date)
        guard let weekdays = range(of: .weekday, in: .weekOfYear, for: date) else {
            return []
        }
        return (weekdays.lowerBound ..< weekdays.upperBound)
            .flatMap { date(byAdding: .day, value: $0 - dayOfWeek, to: date) }
    }
}

// 使用方式
let calendar = Calendar.current
let thisWeekDates = calendar.datesOfWeek(for: Date())

// 获取上周日期
guard let lastWeekDate = calendar.date(byAdding: .day, value: -7, to: Date()) else {
    fatalError("Failed to get last week date")
}
let lastWeekDates = calendar.datesOfWeek(for: lastWeekDate)

内容的提问来源于stack exchange，提问作者user2786