如何使用Swift4中的Codable转换带有可选小数秒的日期字符串

Question

我正在用Swift的Codable替换旧的JSON解析代码,并且遇到了一些麻烦.我想这不是一个可编码的问题,因为它是一个DateFormatter问题.

从结构开始

 struct JustADate: Codable {
    var date: Date
 }

和一个json字符串

let json = """
  { "date": "2017-06-19T18:43:19Z" }
"""

现在让我们解码

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601

let data = json.data(using: .utf8)!
let justADate = try! decoder.decode(JustADate.self, from: data) //all good

但是,如果我们更改日期以使其具有小数秒,例如:

let json = """
  { "date": "2017-06-19T18:43:19.532Z" }
"""

现在它打破了.日期有时会以小秒数回归,有时则不会.我以前解决它的方式是在我的映射代码中我有一个转换函数,它尝试使用和不使用小数秒的dateFormats.我不太确定如何使用Codable来处理它.有什么建议？

Answer 1

您可以使用两个不同的日期格式化程序(有和没有分数秒)并创建自定义DateDecodingStrategy.如果在解析API返回的日期时出现故障,您可以按照@PauloMattos在评论中的建议抛出DecodingError:

iOS 9,macOS 10.9,tvOS 9,watchOS 2,Xcode 9或更高版本

自定义ISO8601 DateFormatter:

extension Formatter {
    static let iso8601: DateFormatter = {
        let formatter = DateFormatter()
        formatter.calendar = Calendar(identifier: .iso8601)
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.timeZone = TimeZone(secondsFromGMT: 0)
        formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSXXXXX"
        return formatter
    }()
    static let iso8601noFS: DateFormatter = {
        let formatter = DateFormatter()
        formatter.calendar = Calendar(identifier: .iso8601)
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.timeZone = TimeZone(secondsFromGMT: 0)
        formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ssXXXXX"
        return formatter
    }()
}

习俗DateDecodingStrategy和Error:

extension JSONDecoder.DateDecodingStrategy {
    static let customISO8601 = custom {
        let container = try $0.singleValueContainer()
        let string = try container.decode(String.self)
        if let date = Formatter.iso8601.date(from: string) ?? Formatter.iso8601noFS.date(from: string) {
            return date
        }
        throw DecodingError.dataCorruptedError(in: container, debugDescription: "Invalid date: \(string)")
    }
}

习俗DateEncodingStrategy:

extension JSONEncoder.DateEncodingStrategy {
    static let customISO8601 = custom {
        var container = $1.singleValueContainer()
        try container.encode(Formatter.iso8601.string(from: $0))
    }
}

编辑/更新:

Xcode 9•Swift 4•iOS 11或更高版本

ISO8601DateFormatter现在支持formatOptions .withFractionalSecondsiOS11或更高版本:

extension Formatter {
    static let iso8601: ISO8601DateFormatter = {
        let formatter = ISO8601DateFormatter()
        formatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
        return formatter
    }()
    static let iso8601noFS = ISO8601DateFormatter()
}

海关DateDecodingStrategy和DateEncodingStrategy上面所示的相同.

// Playground testing
struct ISODates: Codable {
    let dateWith9FS: Date
    let dateWith3FS: Date
    let dateWith2FS: Date
    let dateWithoutFS: Date
}
let isoDatesJSON = """
{
"dateWith9FS": "2017-06-19T18:43:19.532123456Z",
"dateWith3FS": "2017-06-19T18:43:19.532Z",
"dateWith2FS": "2017-06-19T18:43:19.53Z",
"dateWithoutFS": "2017-06-19T18:43:19Z",
}
"""
let isoDatesData = Data(isoDatesJSON.utf8)

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .customISO8601

do {
    let isoDates = try decoder.decode(ISODates.self, from: isoDatesData)
    print(Formatter.iso8601.string(from: isoDates.dateWith9FS))   // 2017-06-19T18:43:19.532Z
    print(Formatter.iso8601.string(from: isoDates.dateWith3FS))   // 2017-06-19T18:43:19.532Z
    print(Formatter.iso8601.string(from: isoDates.dateWith2FS))   // 2017-06-19T18:43:19.530Z
    print(Formatter.iso8601.string(from: isoDates.dateWithoutFS)) // 2017-06-19T18:43:19.000Z
} catch {
    print(error)
}

Answer 2

雨燕5

要解析 ISO8601 字符串到日期，您必须使用 DateFormatter。在较新的系统（例如 iOS11+）中，您可以使用 ISO8601DateFormatter。

只要您不知道日期是否包含毫秒，您就应该为每种情况创建 2 个格式化程序。然后，在将 String 解析为 Date 期间，因此使用两者。

适用于旧系统的 DateFormatter

/// Formatter for ISO8601 with milliseconds
lazy var iso8601FormatterWithMilliseconds: DateFormatter = {
    let dateFormatter = DateFormatter()
    dateFormatter.locale = Locale(identifier: "en_US_POSIX")
    dateFormatter.timeZone = TimeZone(abbreviation: "GMT")
    dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZ"

    return dateFormatter
}()

/// Formatter for ISO8601 without milliseconds
lazy var iso8601Formatter: DateFormatter = {
    let dateFormatter = DateFormatter()
    dateFormatter.locale = Locale(identifier: "en_US_POSIX")
    dateFormatter.timeZone = TimeZone(abbreviation: "GMT")
    dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ssZZZZZ"

    return dateFormatter
}()

适用于较新系统的 ISO8601DateFormatter（例如 iOS 11+）

lazy var iso8601FormatterWithMilliseconds: ISO8601DateFormatter = {
    let formatter = ISO8601DateFormatter()

    // GMT or UTC -> UTC is standard, GMT is TimeZone
    formatter.timeZone = TimeZone(abbreviation: "GMT")
    formatter.formatOptions = [.withInternetDateTime,
                               .withDashSeparatorInDate,
                               .withColonSeparatorInTime,
                               .withTimeZone,
                               .withFractionalSeconds]

    return formatter
}()

/// Formatter for ISO8601 without milliseconds
lazy var iso8601Formatter: ISO8601DateFormatter = {
    let formatter = ISO8601DateFormatter()

    // GMT or UTC -> UTC is standard, GMT is TimeZone
    formatter.timeZone = TimeZone(abbreviation: "GMT")
    formatter.formatOptions = [.withInternetDateTime,
                               .withDashSeparatorInDate,
                               .withColonSeparatorInTime,
                               .withTimeZone]

    return formatter
}()

概括

您可以注意到，需要创建 2 个格式化程序。如果你想支持旧系统，它会提供 4 个格式化程序。为了更简单，请查看GitHub 上的 Tomorrow，您可以在其中查看此问题的完整解决方案。

要将字符串转换为日期，请使用：

let date = Date.fromISO("2020-11-01T21:10:56.22+02:00")