Save codable in https://www.raywenderlich.com/160653/design-patterns-ios-using-swift-part-22

codable.swift

 // 1. define Album Codalble
 
 struct Album: Codable {
  let title : String
  let artist : String
  let genre : String
  let coverUrl : String
  let year : String
}

 // 2. save the album as json format
 private var documents: URL {
    return FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
  }
  
  private enum FileNames {
    static let Albums = "albums.json"
  }
  
  func saveAlbums() {
    let url = documents.appendingPathComponent(FileNames.Albums)
    print(url)
    guard let encodedData = try? JSONEncoder().encode(albums) else {
      return
    }
    try? encodedData.write(to: url)
  }
  
 // 3. 放置 album.json 去 main Bundle
 // 4. 更改 Persistency.swift init方法
   init() {
  
    let savedURL = documents.appendingPathComponent(FileNames.Albums)
    var data = try? Data(contentsOf: savedURL)
    if data == nil, let bundleURL = Bundle.main.url(forResource: FileNames.Albums, withExtension: nil) {
      data = try? Data(contentsOf: bundleURL)
    }

    if let albumData = data, let decodedAlbums = try? JSONDecoder().decode([Album].self, from: albumData){
      albums = decodedAlbums
      saveAlbums()
    }
  }