如何在Swift4中使用Codable将日期字符串转换为可选的小数秒
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Codable问题,而是一个DateFormatter问题。
struct JustADate: Codable { var date: Date
}
let json = """ { "date": "2017-06-19T18:43:19Z" }
"""
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,使其具有小数秒,例如:
let json = """ { "date": "2017-06-19T18:43:19.532Z" }
"""
现在坏了。日期有时会以小数秒返回,有时却不会。我用来解决该问题的方法是在映射代码中,我有一个转换函数,该函数尝试使用带和不带小数秒的dateFormats。我不太确定如何使用Codable处理它。有什么建议?
回答:
您可以使用两个不同的日期格式器(带和不带小数秒)并创建自定义的DateDecodingStrategy。如果在解析API返回的日期时失败,则可以按@PauloMattos的建议在注释中引发DecodingError:
自定义ISO8601DateFormatter:
extension Formatter { static let iso8601withFractionalSeconds: 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 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:ssXXXXX"
return formatter
}()
}
习惯DateDecodingStrategy
:
extension JSONDecoder.DateDecodingStrategy { static let customISO8601 = custom {
let container = try $0.singleValueContainer()
let string = try container.decode(String.self)
if let date = Formatter.iso8601withFractionalSeconds.date(from: string) ?? Formatter.iso8601.date(from: string) {
return date
}
throw DecodingError.dataCorruptedError(in: container, debugDescription: "Invalid date: \(string)")
}
}
习惯DateEncodingStrategy
:
extension JSONEncoder.DateEncodingStrategy { static let customISO8601 = custom {
var container = $1.singleValueContainer()
try container.encode(Formatter.iso8601withFractionalSeconds.string(from: $0))
}
}
:
ISO8601DateFormatter
现在支持formatOptions
.withFractionalSeconds
:
extension Formatter { static let iso8601withFractionalSeconds: ISO8601DateFormatter = {
let formatter = ISO8601DateFormatter()
formatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
return formatter
}()
static let iso8601: ISO8601DateFormatter = {
let formatter = ISO8601DateFormatter()
formatter.formatOptions = [.withInternetDateTime]
return formatter
}()
}
习惯DateDecodingStrategy
和DateEncodingStrategy
将与上面显示的相同。
// Playground testingstruct 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.iso8601withFractionalSeconds.string(from: isoDates.dateWith9FS)) // 2017-06-19T18:43:19.532Z
print(Formatter.iso8601withFractionalSeconds.string(from: isoDates.dateWith3FS)) // 2017-06-19T18:43:19.532Z
print(Formatter.iso8601withFractionalSeconds.string(from: isoDates.dateWith2FS)) // 2017-06-19T18:43:19.530Z
print(Formatter.iso8601withFractionalSeconds.string(from: isoDates.dateWithoutFS)) // 2017-06-19T18:43:19.000Z
} catch {
print(error)
}
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