SwiftJSONDecoder提供了一个dateDecodingStrategy属性，它允许我们定义如何根据DateFormatter对象来解释传入的日期字符串。
但是，我目前正在使用一个返回日期字符串 ( yyyy-MM-dd) 和日期时间字符串 () 的 API yyyy-MM-dd HH:mm:ss，具体取决于属性。有没有办法JSONDecoder处理这个，因为提供的DateFormatter对象一次只能处理一个dateFormat？
一个笨拙的解决方案是重写随附的Decodable模型以仅接受字符串作为它们的属性并提供公共Dategetter/setter 变量，但这对我来说似乎是一个糟糕的解决方案。有什么想法吗？
请尝试配置与此类似的解码器：
lazy var decoder: JSONDecoder = {
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .custom({ (decoder) -> Date in
let container = try decoder.singleValueContainer()
let dateStr = try container.decode(String.self)
// possible date strings: "2016-05-01", "2016-07-04T17:37:21.119229Z", "2018-05-20T15:00:00Z"
let len = dateStr.count
var date: Date? = nil
if len == 10 {
date = dateNoTimeFormatter.date(from: dateStr)
} else if len == 20 {
date = isoDateFormatter.date(from: dateStr)
} else {
date = self.serverFullDateFormatter.date(from: dateStr)
}
guard let date_ = date else {
throw DecodingError.dataCorruptedError(in: container, debugDescription: "Cannot decode date string \(dateStr)")
}
print("DATE DECODER \(dateStr) to \(date_)")
return date_
})
return decoder
}()
有几种方法可以解决这个问题：
DateFormatter子类，它首先尝试日期时间字符串格式，然后如果失败，则尝试纯日期格式.custom Date解码策略，其中您要求Decodera singleValueContainer()，解码一个字符串，并在传递解析的日期之前将其传递给您想要的任何格式化程序Date您可以围绕提供自定义的类型创建一个包装器init(from:)并encode(to:)执行此操作（但这并不比.custom策略更好）init(from:)使用这些日期的所有类型提供自定义并在其中尝试不同的事情总而言之，前两种方法可能是最简单和最干净的——您将保留默认的综合实现Codable无处不在，而不会牺牲类型安全。
尝试这个。（迅速 4）
let formatter = DateFormatter()
var decoder: JSONDecoder {
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .custom { decoder in
let container = try decoder.singleValueContainer()
let dateString = try container.decode(String.self)
formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
if let date = formatter.date(from: dateString) {
return date
}
formatter.dateFormat = "yyyy-MM-dd"
if let date = formatter.date(from: dateString) {
return date
}
throw DecodingError.dataCorruptedError(in: container,
debugDescription: "Cannot decode date string \(dateString)")
}
return decoder
}
斯威夫特 5
实际上基于使用JSONDecoder扩展的@BrownsooHan 版本
JSONDecoder+dateDecodingStrategyFormatters.swift
extension JSONDecoder {
/// Assign multiple DateFormatter to dateDecodingStrategy
///
/// Usage :
///
/// decoder.dateDecodingStrategyFormatters = [ DateFormatter.standard, DateFormatter.yearMonthDay ]
///
/// The decoder will now be able to decode two DateFormat, the 'standard' one and the 'yearMonthDay'
///
/// Throws a 'DecodingError.dataCorruptedError' if an unsupported date format is found while parsing the document
var dateDecodingStrategyFormatters: [DateFormatter]? {
@available(*, unavailable, message: "This variable is meant to be set only")
get { return nil }
set {
guard let formatters = newValue else { return }
self.dateDecodingStrategy = .custom { decoder in
let container = try decoder.singleValueContainer()
let dateString = try container.decode(String.self)
for formatter in formatters {
if let date = formatter.date(from: dateString) {
return date
}
}
throw DecodingError.dataCorruptedError(in: container, debugDescription: "Cannot decode date string \(dateString)")
}
}
}
}
添加只能设置的变量有点笨拙，但是您可以轻松地var dateDecodingStrategyFormatters通过以下方式进行转换func setDateDecodingStrategyFormatters(_ formatters: [DateFormatter]? )
用法
假设您已经DateFormatter在代码中定义了几个 s，如下所示：
extension DateFormatter {
static let standardT: DateFormatter = {
var dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss"
return dateFormatter
}()
static let standard: DateFormatter = {
var dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
return dateFormatter
}()
static let yearMonthDay: DateFormatter = {
var dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
return dateFormatter
}()
}
您现在可以通过设置直接将这些分配给解码器dateDecodingStrategyFormatters：
// Data structure
struct Dates: Codable {
var date1: Date
var date2: Date
var date3: Date
}
// The Json to decode
let jsonData = """
{
"date1": "2019-05-30 15:18:00",
"date2": "2019-05-30T05:18:00",
"date3": "2019-04-17"
}
""".data(using: .utf8)!
// Assigning mutliple DateFormatters
let decoder = JSONDecoder()
decoder.dateDecodingStrategyFormatters = [ DateFormatter.standardT,
DateFormatter.standard,
DateFormatter.yearMonthDay ]
do {
let dates = try decoder.decode(Dates.self, from: jsonData)
print(dates)
} catch let err as DecodingError {
print(err.localizedDescription)
}
旁注
我再次意识到将 a 设置dateDecodingStrategyFormatters为var有点 hacky，我不推荐它，您应该定义一个函数。但是，这样做是个人喜好。
面对同样的问题，我写了以下扩展：
extension JSONDecoder.DateDecodingStrategy {
static func custom(_ formatterForKey: @escaping (CodingKey) throws -> DateFormatter?) -> JSONDecoder.DateDecodingStrategy {
return .custom({ (decoder) -> Date in
guard let codingKey = decoder.codingPath.last else {
throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "No Coding Path Found"))
}
guard let container = try? decoder.singleValueContainer(),
let text = try? container.decode(String.self) else {
throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Could not decode date text"))
}
guard let dateFormatter = try formatterForKey(codingKey) else {
throw DecodingError.dataCorruptedError(in: container, debugDescription: "No date formatter for date text")
}
if let date = dateFormatter.date(from: text) {
return date
} else {
throw DecodingError.dataCorruptedError(in: container, debugDescription: "Cannot decode date string \(text)")
}
})
}
}
此扩展允许您为 JSONDecoder 创建一个 DateDecodingStrategy，以处理同一 JSON 字符串中的多种不同日期格式。该扩展包含一个函数，该函数需要实现为您提供 CodingKey 的闭包，并且由您为所提供的密钥提供正确的 DateFormatter。
假设您有以下 JSON：
{
"publication_date": "2017-11-02",
"opening_date": "2017-11-03",
"date_updated": "2017-11-08 17:45:14"
}
以下结构：
struct ResponseDate: Codable {
var publicationDate: Date
var openingDate: Date?
var dateUpdated: Date
enum CodingKeys: String, CodingKey {
case publicationDate = "publication_date"
case openingDate = "opening_date"
case dateUpdated = "date_updated"
}
}
然后要解码 JSON，您将使用以下代码：
let dateFormatterWithTime: DateFormatter = {
let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
return formatter
}()
let dateFormatterWithoutTime: DateFormatter = {
let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd"
return formatter
}()
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .custom({ (key) -> DateFormatter? in
switch key {
case ResponseDate.CodingKeys.publicationDate, ResponseDate.CodingKeys.openingDate:
return dateFormatterWithoutTime
default:
return dateFormatterWithTime
}
})
let results = try? decoder.decode(ResponseDate.self, from: data)
它有点冗长，但更灵活：用另一个 Date 类包装日期，并为其实现自定义序列化方法。例如：
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
class MyCustomDate: Codable {
var date: Date
required init?(_ date: Date?) {
if let date = date {
self.date = date
} else {
return nil
}
}
public func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
let string = dateFormatter.string(from: date)
try container.encode(string)
}
required public init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
let raw = try container.decode(String.self)
if let date = dateFormatter.date(from: raw) {
self.date = date
} else {
throw DecodingError.dataCorruptedError(in: container, debugDescription: "Cannot parse date")
}
}
}
因此，现在您独立于.dateDecodingStrategy并且.dateEncodingStrategy您的MyCustomDate日期将使用指定的格式进行解析。在课堂上使用它：
class User: Codable {
var dob: MyCustomDate
}
实例化
user.dob = MyCustomDate(date)
使用单个编码器无法做到这一点。您最好的选择是自定义encode(to encoder:)和init(from decoder:)方法，并为其中一个值提供您自己的翻译，而为另一个值保留内置的日期策略。
userInfo为此目的，可能值得考虑将一个或多个格式化程序传递给对象。
向KeyedDecodingContainer添加扩展
extension KeyedDecodingContainer {
func decodeDate(forKey key: KeyedDecodingContainer<K>.Key, withPossible formats: [DateFormatter]) throws -> Date? {
for format in formats {
if let date = format.date(from: try self.decode(String.self, forKey: key)) {
return date
}
}
throw DecodingError.dataCorruptedError(forKey: key, in: self, debugDescription: "Date string does not match format expected by formatter.")
}
}
并使用'try container.decodeDate(forKey: 'key', withPossible: [.iso8601Full, .yyyyMMdd])'
完整的解决方案在这里：
import Foundation
extension DateFormatter {
static let iso8601Full: DateFormatter = {
let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
formatter.calendar = Calendar(identifier: .iso8601)
formatter.timeZone = TimeZone(secondsFromGMT: 0)
formatter.locale = Locale(identifier: "en_US_POSIX")
return formatter
}()
static let yyyyMMdd: DateFormatter = {
let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd"
formatter.calendar = Calendar(identifier: .iso8601)
formatter.timeZone = TimeZone(secondsFromGMT: 0)
formatter.locale = Locale(identifier: "en_US_POSIX")
return formatter
}()
}
public struct RSSFeed: Codable {
public let releaseDate: Date?
public let releaseDateAndTime: Date?
}
extension RSSFeed {
public init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
releaseDate = try container.decodeDate(forKey: .releaseDate, withPossible: [.iso8601Full, .yyyyMMdd])
releaseDateAndTime = try container.decodeDate(forKey: .releaseDateAndTime, withPossible: [.iso8601Full, .yyyyMMdd])
}
}
extension KeyedDecodingContainer {
func decodeDate(forKey key: KeyedDecodingContainer<K>.Key, withPossible formats: [DateFormatter]) throws -> Date? {
for format in formats {
if let date = format.date(from: try self.decode(String.self, forKey: key)) {
return date
}
}
throw DecodingError.dataCorruptedError(forKey: key, in: self, debugDescription: "Date string does not match format expected by formatter.")
}
}
let json = """
{
"releaseDate":"2017-11-12",
"releaseDateAndTime":"2017-11-16 02:02:55"
}
"""
let data = Data(json.utf8)
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .formatted(DateFormatter.iso8601Full)
let rssFeed = try! decoder.decode(RSSFeed.self, from: data)
let feed = rssFeed
print(feed.releaseDate, feed.releaseDateAndTime)
如果您在单个模型中有多个不同格式的日期，则很难.dateDecodingStrategy为每个日期申请。
在这里查看https://gist.github.com/romanroibu/089ec641757604bf78a390654c437cb0以获得方便的解决方案