日历

1. Calendar.Component

2. 指定日期范围

extension Date {
    var rangeOfDay: Range<Int> {
        Calendar.current.range(of: .day, in: .month, for: self)!
    }
    
    func firstDay(in component: Calendar.Component) -> Date {
        var dateComponents = Calendar.current.dateComponents([.year, .month, .day, .hour, .minute, .second], from: self)
        
        switch component {
        case .year:
            dateComponents.month = 1
            fallthrough
        case .month:
            dateComponents.day = 1
            fallthrough
        case .day:
            dateComponents.hour = 0
            dateComponents.minute = 0
            dateComponents.second = 0
        default:
            break
        }
        return Calendar.current.date(from: dateComponents) ?? self
    }
    
    func endDay(in component: Calendar.Component) -> Date {
        var dateComponents = Calendar.current.dateComponents([.year, .month, .day, .hour, .minute, .second], from: self)
        
        switch component {
        case .year:
            dateComponents.month = 12
            fallthrough
        case .month:
            dateComponents.day = rangeOfDay.max() ?? 0
            fallthrough
        case .day:
            dateComponents.hour = 23
            dateComponents.minute = 59
            dateComponents.second = 59
        default:
            break
        }
        return Calendar.current.date(from: dateComponents) ?? self
    }
}
let range = Date().rangeOfDay
/// 1..<31
let firstDate = Date().firstDay(in: .year)
/// 2018-12-31 16:00:00 +0000(2019-01-01 00:00:00 +8000)
let endDate = Date().endDay(in: .year)
/// 2019-12-30 15:59:59 +0000(2019-12-30 23:59:59 +80000)

时区

1. 获取已知时区

TimeZone.knownTimeZoneIdentifiers

2. 当前时区名称和缩写

let zone = TimeZone.current
/// 名称
zone.identifier
/// 缩写
zone.abbreviation()
/// 当前时区与零时区的间隔秒数
zone.secondsFromGMT()

字符串转换成时间

/// 北京时间东八区，比美国快了13小时
let timeStr = "2018-12-12 10:48:46 GTM +8:00"
let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd HH:mm:ss ZZZZ"
let date = formatter.date(from: timeStr)

/// 24小时制
formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
formatter.string(from: date!)

/// 中国：年月日 上下午 时间
formatter.locale = Locale(identifier: "zh_CN")
formatter.dateStyle = .medium
formatter.timeStyle = .medium
formatter.string(from: date!)

DateComponents转化为时间

extension Date {
    init?(components: DateComponents) {
        guard let date = Calendar.current.date(from: components) else {
            return nil
        }
        self = date
    }

    static func + (lhs: inout Date, rhs: DateComponents) -> Date? {
        return Calendar.current.date(byAdding: rhs, to: lhs)
    }

    static func - (lhs: inout Date, rhs: DateComponents) -> Date? {
        var right = rhs

        right.era = rhs.era != nil ? -rhs.era! : nil

        right.year = rhs.year != nil ? -rhs.year! : nil
        right.month = rhs.month != nil ? -rhs.month! : nil
        right.day = rhs.day != nil ? -rhs.day! : nil

        right.hour = rhs.hour != nil ? -rhs.hour! : nil
        right.minute = rhs.minute != nil ? -rhs.minute! : nil
        right.second = rhs.second != nil ? -rhs.second! : nil
        right.nanosecond = rhs.nanosecond != nil ? -rhs.nanosecond! : nil

        return Calendar.current.date(byAdding: right, to: lhs)
    }
}

let components = DateComponents(year: 2001, month: 5, day: 10)
let date = Date(components: components)
/// Optional(2001-05-09 16:00:00 +0000)
let add = DateComponents(month: 5, day: 5)
let resultDate = date! + add
/// Optional(2001-10-14 16:00:00 +0000)
let resultDate1 = date - add
/// Optional(2000-12-04 16:00:00 +0000)

时间组件化

extension Date {
    func value(for component: Calendar.Component) -> Int {
        var dateComponents = Calendar.current.dateComponents([component], from: self)
      
        switch component {
        case .quarter:
            let month = value(for: .month)
            
            if month < 4 {
                dateComponents.quarter = 1
            } else if month < 7 {
                dateComponents.quarter = 2
            } else if month <= 10 {
                dateComponents.quarter = 3
            } else {
                dateComponents.quarter = 4
            }
        case .calendar, .timeZone:
            
            if dateComponents.calendar == nil {
                dateComponents.calendar = Calendar.current
            }
        default:
            break
        }
        return dateComponents.value(for: component) ?? 0
    }
}

let date0 = Date().value(for: .year)
/// 2019