Plist编码和解码回字典[String：Decodable] [英] Plist encoding and decoding back to Dictionary [String:Decodable]

问题描述

我希望能够将[String：Codable]类型的Dictionary保存到plist并恢复原样。我试过了，但是会引发错误：

I want to be able to save Dictionary of type [String:Codable] to plist and recover back as same. I tried this but it throws errors:

  let dictionary:[String:Any] = ["point":CGPoint(1,1), "value": 10, "key" : "testKey"] 

   do { 
        let url = FileManager.default.temporaryDirectory.appendingPathComponent("test.plist")
        try savePropertyList(dictionary, toURL: url)
        buildFromPlist(url)
      } catch {
        print(error)
    }
  


    private func savePropertyList(_ plist: Any, toURL url:URL) throws
   {
    let plistData = try PropertyListSerialization.data(fromPropertyList: plist, format: .xml, options: 0)
    try plistData.write(to: url)
   }

  private func buildFromPlist(_ url:URL)
  {
       do {
          let data = try Data(contentsOf: url)
          let decoder = PropertyListDecoder()
          let dictionary = try decoder.decode([String:Decodable], from: data)
          NSLog("\(dictionary)")
      } catch {
           NSLog("Error decoding \(error)")
      }
   
    
   }

但是我在解码功能中遇到了构建错误：

But I get build errors in decode function:

  Value of protocol type 'Decodable' cannot conform to 'Decodable'; only struct/enum/class types can conform to protocols

我不知道如何读回保存到plist文件的字典？

I wonder how I read back the dictionary I saved to plist file?

编辑：即使savePropertyList在运行时也由于诸如CGPoint和CGAffineTransform之类的对象而失败，并显示错误-

Even savePropertyList fails at runtime with objects such as CGPoint and CGAffineTransform with the error -

 "Property list invalid for format: 100 (property lists cannot contain objects of type 'CFType')" UserInfo={NSDebugDescription=Property list invalid for format: 100 (property lists cannot contain objects of type 'CFType')}

我想知道我们如何才能将Codable对象写入plist并恢复回来？

I wonder how can we write Codable objects to plist and recover back?

推荐答案

这是行不通的，因为 decoder.decode 行必须是具体类型。而 [String：Decodable] 而不尾随 .self 会引发另一个错误。

This cannot work because the type in the decoder.decode line must be a concrete type. And [String:Decodable] without trailing .self will throw another error.

Codable 协议的目标是序列化自定义结构或类，从而使字典成为结构

The goal of the Codable protocol is to serialize custom structs or classes so make your dictionary a struct

struct MyType : Codable {
    let point : CGPoint
    let value : Int
    let key : String
}

并将其编码。在解码部分中写

and encode this. In the decoding part write

let item = try decoder.decode(MyType.self, from: data)

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