如何配置DateFormatter捕获微秒

  • Z时代
  • 2024-01-10
  • 分类：问答

iOS Date()返回日期的精度至少为微秒。

我通过调用Date().timeIntervalSince1970导致1490891661.074981

然后，我需要将日期转换为微秒精度的字符串。

我使用DateFormatter以下方式：

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

导致

"2017-03-30T16:34:21.075000Z"

现在，如果我们比较两个结果：

1490891661.074981并且"2017-03-30T16:34:21.075000Z"

我们可以注意到将DateFormatter日期舍入为毫秒精度，同时仍然以微秒为单位显示零。

有人知道如何配置，DateFormatter以便我可以保持微秒并获得正确的结果"2017-03-30T16:34:21.074981Z"吗？

回答：

感谢@MartinR解决了我的问题的上半部分，并感谢@ForestKunecke给了我一些解决问题的后半部分的技巧。

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：

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

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