如何配置DateFormatter捕获微秒 [英] How to configure DateFormatter to capture microseconds

问题描述

iOS Date（）返回日期的精度至少为微秒。

我通过调用 Date（）来检查此语句.timeIntervalSince1970 会导致 1490891661.074981

iOS Date() returns date with at least microsecond precision.
I checked this statement by calling Date().timeIntervalSince1970 which results in 1490891661.074981

然后我需要将日期转换为字符串微秒精度。

我以以下方式使用 DateFormatter ：

Then I need to convert date into string with microsecond precision.
I am using DateFormatter in following way:

let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSSSSZZZZZ"
print(formatter.string(from: date))

这会导致

2017-03 -30T16：34：21.075000Z

现在，如果我们比较两个结果：

1490891661.074981 和 2017-03-30T16：34：21.075000Z

我们可以注意到 DateFormatter 将日期四舍五入为毫秒精度，同时仍然显示零微秒。

Now if we compare two results:
1490891661.074981 and "2017-03-30T16:34:21.075000Z"
we can notice that DateFormatter rounds date to millisecond precision while still presenting zeros for microseconds.

有人知道如何配置 DateFormatter 所以我可以p微秒并获得正确结果： 2017-03-30T16：34：21.074981Z ？

Does anybody know how to configure DateFormatter so I can keep microseconds and get correct result: "2017-03-30T16:34:21.074981Z"?

推荐答案

感谢@MartinR解决了我的问题的上半部分，并感谢@ForestKunecke给了我解决问题的后半部分的技巧。

Thanks to @MartinR for solving first half of my problem and to @ForestKunecke for giving me tips how to solve second half of the problem.

基于他们的帮助，我创建了现成的解决方案，该解决方案可以毫秒精度将字符串中的日期转换为字符串，反之亦然：

Based on their help I created ready to use solution which converts date from string and vice versa with millisecond precision:

public final class MicrosecondPrecisionDateFormatter: DateFormatter {

    private let microsecondsPrefix = "."

    override public init() {
        super.init()
        locale = Locale(identifier: "en_US_POSIX")
        timeZone = TimeZone(secondsFromGMT: 0)
    }

    required public init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override public func string(from date: Date) -> String {
        dateFormat = "yyyy-MM-dd'T'HH:mm:ss"
        let components = calendar.dateComponents(Set([Calendar.Component.nanosecond]), from: date)

        let nanosecondsInMicrosecond = Double(1000)
        let microseconds = lrint(Double(components.nanosecond!) / nanosecondsInMicrosecond)

        // Subtract nanoseconds from date to ensure string(from: Date) doesn't attempt faulty rounding.
        let updatedDate = calendar.date(byAdding: .nanosecond, value: -(components.nanosecond!), to: date)!
        let dateTimeString = super.string(from: updatedDate)

        let string = String(format: "%@.%06ldZ",
                            dateTimeString,
                            microseconds)

        return string
    }

    override public func date(from string: String) -> Date? {
        dateFormat = "yyyy-MM-dd'T'HH:mm:ssZZZZZ"

        guard let microsecondsPrefixRange = string.range(of: microsecondsPrefix) else { return nil }
        let microsecondsWithTimeZoneString = String(string.suffix(from: microsecondsPrefixRange.upperBound))

        let nonDigitsCharacterSet = CharacterSet.decimalDigits.inverted
        guard let timeZoneRangePrefixRange = microsecondsWithTimeZoneString.rangeOfCharacter(from: nonDigitsCharacterSet) else { return nil }

        let microsecondsString = String(microsecondsWithTimeZoneString.prefix(upTo: timeZoneRangePrefixRange.lowerBound))
        guard let microsecondsCount = Double(microsecondsString) else { return nil }

        let dateStringExludingMicroseconds = string
            .replacingOccurrences(of: microsecondsString, with: "")
            .replacingOccurrences(of: microsecondsPrefix, with: "")

        guard let date = super.date(from: dateStringExludingMicroseconds) else { return nil }
        let microsecondsInSecond = Double(1000000)
        let dateWithMicroseconds = date + microsecondsCount / microsecondsInSecond

        return dateWithMicroseconds
    }
}

用法：

let formatter = MicrosecondPrecisionDateFormatter()
let date = Date(timeIntervalSince1970: 1490891661.074981)
let formattedString = formatter.string(from: date) // 2017-03-30T16:34:21.074981Z

这篇关于如何配置DateFormatter捕获微秒的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！