我正在开发一个简单的音乐音序器应用程序。这类应用往往具有必须保存/加载的复杂数据结构,因此在 Swift4 中引入 Codable
协议(protocol)对我来说完全是个好消息。
我的问题是:
我必须拥有不可编码的属性(property)。它不必编码,因为它是一个临时变量,仅在应用程序处于事件状态时保持事件状态。
所以我只是尝试通过实现 CodingKey
来排除,但编译器仍然给我错误“Type 'Song' does not conform to protocol 'Decodable'”。
具体来说,我想在下面的代码中排除“musicSequence”。
class Song : Codable { //Type 'Song' does not conform to protocol 'Decodable'
var songName : String = "";
var tempo : Double = 120;
// Musical structure
var tracks : [Track] = [] // "Track" is my custom class, which conforms Codable as well
// Tones
var tones = [Int : ToneSettings] (); // ToneSettings is also my custom Codable class
var musicSequence : MusicSequence? = nil; // I get the error because of this line
private enum CodingKeys: String, CodingKey {
case songName
case tempo
case tracks
case tones
}
func createMIDISequence () {
// Create MIDI sequence based on "tracks" above
// and keep it as instance variable "musicSequence"
}
}
有没有人有什么想法?
最佳答案
(请参阅下面的奇怪事件。)
您对 CodingKeys
的使用已经在处理您的编码问题。您仍然可以免费获得它。但是您需要告诉系统如何手动处理解码:
required init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
songName = try values.decode(String.self, forKey: .songName)
tempo = try values.decode(Double.self, forKey: .tempo)
tracks = try values.decode([Track].self, forKey: .tracks)
tones = try values.decode([Int: ToneSettings].self, forKey: .tones)
}
相当 还不够聪明,无法弄清楚 musicSequence
可以而且应该默认为 nil
(也许这无论如何都太聪明了) .
可能值得在 bugs.swift.org 上打开一个缺陷来要求这个 Decodable 是自动的。在您提供 CodingKeys
并且有默认值的情况下,它应该能够弄清楚。
编辑:当我第一次回答这个问题时,我完全重复了你的错误。但是当我再次尝试重新复制您的代码时,错误并没有出现。以下代码在 playground 中编译和运行:
import Foundation
struct Track: Codable {}
struct ToneSettings: Codable {}
struct MusicSequence {}
class Song : Codable { //Type 'Song' does not conform to protocol 'Decodable'
var songName : String = "";
var tempo : Double = 120;
// Musical structure
var tracks : [Track] = [] // "Track" is my custom class, which conforms Codable as well
// Tones
var tones = [Int : ToneSettings] (); // ToneSettings is also my custom Codable class
var musicSequence : MusicSequence? = nil; // I get the error because of this line
private enum CodingKeys: String, CodingKey {
case songName
case tempo
case tracks
case tones
}
func createMIDISequence () {
// Create MIDI sequence based on "tracks" above
// and keep it as instance variable "musicSequence"
}
}
let song = Song()
let data = try JSONEncoder().encode(song)
String(data: data, encoding: .utf8)
let song2 = try JSONDecoder().decode(Song.self, from: data)
我想知道这里是否存在编译器错误;确保使用新的测试版对此进行测试。
关于ios - swift 4 可编码 : Cannot exclude a property,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/45557262/