Swift自定义编码，用于将整数时间编码为漂亮的字符串。

huangapple
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英文:

Swift custom encode for encoding Int time like pretty string

问题

I have a custom object stored in a Struct:

  1. struct Event {
  2.    let type: String
  3.    let value: String
  4.    let time: Int
  5. }

其中，time 是以毫秒为单位的 Unix 时间。在应用程序中，我有一个可滚动的文本字段，当我以 JSON 格式打印此事件时：

  1. {
  2.    "type" : "rain",
  3.    "value" : "0.5",
  4.    "time" : 1681663944
  5. }

但是对于 time 参数，我想将 Unix 时间转换为人类可读的形式（即 16/04/2023），因此我需要自定义该参数的编码方式。问题是，所有我的对象都符合此协议，因此我可以免费使用Codable的toJsonString()方法。

  1. protocol BaseObject: Codable {
  2.     
  3. }
  5. extension BaseObject {
  6.     func toJsonString() -> String {
  7.         let jsonEncoder = JSONEncoder()
  8.         do {
  9.             let jsonData = try jsonEncoder.encode(self)
  10.             let json = String(data: jsonData, encoding: String.Encoding.utf8)
  11.             return json ?? ""
  12.         } catch {
  13.             return ""
  14.         }
  15.     }
  16. }

因此，我不需要为每个对象单独编写 toJsonString() 方法。天真的解决方案应该是为每个对象编写自定义的 toJsonString()，但我有很多结构体，如果我找到了一个巧妙的方法来拦截 time 属性，我可以用这种类型覆盖应用程序中的所有属性的编码表示。

有什么想法吗？

谢谢。

编辑

目前，我找到了这个解决方案：

  1. func toJsonString() -> String {
  2.         let jsonEncoder = JSONEncoder()
  3.         do {
  4.             let jsonData = try jsonEncoder.encode(self)
  5.             var modData = Data()
  6.             
  7.             if var dict = jsonData.toDictionary() {
  8.                 
  9.                 dict.keys.filter{ $0.contains("time") }.forEach { key in
  10.                     if let t = dict[key] as? Int {
  11.                         dict[key] = t.toStringDate()
  12.                     }
  13.                 }
  14.                 
  15.                 modData = dict.toData()
  16.             }
  17.             
  18.             let json = String(data: modData, encoding: String.Encoding.utf8)
  19.             return json ?? ""
  20.         } catch {
  21.             return ""
  22.         }
  23.     }
英文:

I have a custom object stored in a Struct:

  1. struct Event {
  2.    let type: String
  3.    let value: String
  4.    let time: Int
  5. }

where time is a UnixTime in millis. In the App I have a scrollable text field when I print this event in json format

  1. {
  2.    "type" : "rain",
  3.    "value" : "0.5",
  4.    "time" : 1681663944
  5. }

but for time parameter I would like to convert the UnixTime in a human readable form (i.e. 16/04/2023), so I need to customize haw this parameter is encoded. The problem is that all my objects are conforms to this protocol, so I have the toJsonString() method for free, based on the power of Codable.

  1. protocol BaseObject: Codable {
  2.     
  3. }
  5. extension BaseObject {
  6.     func toJsonString() -> String {
  7.         let jsonEncoder = JSONEncoder()
  8.         do {
  9.             let jsonData = try jsonEncoder.encode(self)
  10.             let json = String(data: jsonData, encoding: String.Encoding.utf8)
  11.             return json ?? ""
  12.         } catch {
  13.             return ""
  14.         }
  15.     }
  16. }

So, I don't have a toJsonString() method for each object separately. Naïve solution should be write a custom toJsonString() for each object, but I have a lot of struct and if I found a smart way to intercept time attributes I can override the encode representation of all attributes in the App with this type.

Ideas ?

Thanks.

EDIT

For now I found this solution:

  1. func toJsonString() -> String {
  2.         let jsonEncoder = JSONEncoder()
  3.         do {
  4.             let jsonData = try jsonEncoder.encode(self)
  5.             var modData = Data()
  6.             
  7.             if var dict = jsonData.toDictionary() {
  8.                 
  9.                 dict.keys.filter{ $0.contains("time") }.forEach { key in
  10.                     if let t = dict[key] as? Int {
  11.                         dict[key] = t.toStringDate()
  12.                     }
  13.                 }
  14.                 
  15.                 modData = dict.toData()
  16.             }
  17.             
  18.             let json = String(data: modData, encoding: String.Encoding.utf8)
  19.             return json ?? ""
  20.         } catch {
  21.             return ""
  22.         }
  23.     }

答案1

得分: 1

你可以使用属性包装器来为特定属性提供自定义编码行为：

  1. import Foundation
  3. @propertyWrapper
  4. struct PrettyEncodedDate {
  5.    static let formatter = {
  6.       let df = DateFormatter()
  7.       // 自定义日期格式化程序
  8.       df.dateStyle = .full
  9.       return df
  10.    }()
  11.    
  12.    let wrappedValue: Date
  13. }
  15. extension PrettyEncodedDate: Decodable {
  16.    struct InvalidDateError: Error {
  17.       let dateString: String
  18.    }
  19.    
  20.    init(from decoder: Decoder) throws {
  21.       let container = try decoder.singleValueContainer()
  22.       let dateString = try container.decode(String.self)
  23.       guard let date = Self.formatter.date(from: dateString) else {
  24.          throw InvalidDateError(dateString: dateString)
  25.       }
  26.       self.init(wrappedValue: date)
  27.    }
  28. }
  30. extension PrettyEncodedDate: Encodable {
  31.    func encode(to encoder: Encoder) throws {
  32.       var container = encoder.singleValueContainer()
  33.       let formattedDate = Self.formatter.string(from: self.wrappedValue)
  34.       try container.encode(formattedDate)
  35.    }
  36. }

这是一个示例用法：

  1. struct Event: Codable {
  2.    let type: String
  3.    let value: String
  4.    @PrettyEncodedDate var time: Date
  5. }
  8. let encoder = JSONEncoder()
  9. encoder.outputFormatting = .prettyPrinted
  11. let event = Event(type: "some type", value: "some value", time: Date.now)
  12. let prettyJSON = try encoder.encode(event)
  13. print(String(data: prettyJSON, encoding: .utf8)!)

这将打印：

  1. {
  2.   "type" : "some type",
  3.   "value" : "some value",
  4.   "time" : "Sunday, April 16, 2023"
  5. }

这依赖于 time 是一个 Date（它可能应该是的）。如果必须保持为 Int（虽然我建议不要这样做），你可以调整属性包装器以更改当前的行为（String -> Date，Date -> String）以添加额外的处理步骤（String -> Date -> Int，Int -> Date -> String）。

英文:

You can use a property wrapper to hook in and give custom encoding behaviour for a specific property:

  1. import Foundation
  3. @propertyWrapper
  4. struct PrettyEncodedDate {
  5.    static let formatter = {
  6.       let df = DateFormatter()
  7.       // Customize the date formatter however you'd like
  8.       df.dateStyle = .full
  9.       return df
  10.    }()
  11.    
  12.    let wrappedValue: Date
  13. }
  15. extension PrettyEncodedDate: Decodable {
  16.    struct InvalidDateError: Error {
  17.       let dateString: String
  18.    }
  19.    
  20.    init(from decoder: Decoder) throws {
  21.       let container = try decoder.singleValueContainer()
  22.       let dateString = try container.decode(String.self)
  23.       guard let date = Self.formatter.date(from: dateString) else {
  24.          throw InvalidDateError(dateString: dateString)
  25.       }
  26.       self.init(wrappedValue: date)
  27.    }
  28. }
  30. extension PrettyEncodedDate: Encodable {
  31.    func encode(to encoder: Encoder) throws {
  32.       var container = encoder.singleValueContainer()
  33.       let formattedDate = Self.formatter.string(from: self.wrappedValue)
  34.       try container.encode(formattedDate)
  35.    }
  36. }

Here's an example usage:

  1. struct Event: Codable {
  2.    let type: String
  3.    let value: String
  4.    @PrettyEncodedDate var time: Date
  5. }
  8. let encoder = JSONEncoder()
  9. encoder.outputFormatting = .prettyPrinted
  11. let event = Event(type: "some type", value: "some value", time: Date.now)
  12. let prettyJSON = try encoder.encode(event)
  13. print(String(data: prettyJSON, encoding: .utf8)!)

Which prints:

  1. {
  2.   "type" : "some type",
  3.   "value" : "some value",
  4.   "time" : "Sunday, April 16, 2023"
  5. }

This relies on time to be a Date (which it probably should be). If it must stay an Int (though I'd caution against that), you can tweak the property wrapper to change the current behaviour (String -> Date, Date -> String) to add an extra processing step (String -> Date -> Int, Int -> Date -> String).

huangapple
  • 本文由 发表于 2023年4月17日 01:02:27
  • 转载请务必保留本文链接：https://go.coder-hub.com/76029189.html
  • codable
  • encodable
  • json
  • swift
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