swift - 在 UserDefaults 中保存不同对象类型的数组
问题描述
我有两个班,广播和播客,媒体班的孩子。我正在尝试将一系列媒体(带有收音机和播客)保存到 UserDefaults,但是当我取回它时,我只有媒体(我正在丢失收音机或播客的信息)。我无法将这些项目投射到 Radio 或 Podcast。
private func saveRecentMediaInData(_ medias:[Media]) {
let encoder = JSONEncoder()
if let encoded = try? encoder.encode(medias) {
UserDefaults.standard.setValue(encoded, forKey: recentMediasKey)
}
}
private func getRecentMediasFromData() -> [Media] {
let defaults = UserDefaults.standard
if let data = defaults.value(forKey: recentMediasKey) as? Data {
let decoder = JSONDecoder()
if let decoded = try? decoder.decode(Array.self, from: data) as [Media] {
return decoded
}
}
return []
}
谢谢
解决方案
该问题与UserDefaults
. 它有一个混合对象数组来解码Codable
。
在这种情况下,解决方案是使用enum
带有关联值的 a:
enum Mixed: Codable {
case radio(Radio)
case podcast(Podcast)
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
if let asRadio = try? container.decode(Radio.self) {
self = .radio(asRadio)
} else if let asPodcast = try? container.decode(Podcast.self) {
self = .podcast(asPodcast)
} else {
fatalError("Oops")
}
}
}
这是一个完整的示例代码:
struct SubClassesCodable {
class Media: Codable, CustomStringConvertible {
var title: String
var description: String {
return "Media: \(title)"
}
}
class Radio: Media {
var channel: Int
enum CodingKeys: String, CodingKey {
case channel
}
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.channel = try container.decode(Int.self, forKey: .channel)
try super.init(from: decoder)
}
override func encode(to encoder: Encoder) throws {
try super.encode(to: encoder)
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(channel, forKey: .channel)
}
override var description: String {
return "Radio: \(title) - \(channel)"
}
}
class Podcast: Media {
var author: String
enum CodingKeys: String, CodingKey {
case author
}
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.author = try container.decode(String.self, forKey: .author)
try super.init(from: decoder)
}
override func encode(to encoder: Encoder) throws {
try super.encode(to: encoder)
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(author, forKey: .author)
}
override var description: String {
return "Podcast: \(title) - \(author)"
}
}
enum Mixed: Codable {
case radio(Radio)
case podcast(Podcast)
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
if let asRadio = try? container.decode(Radio.self) {
self = .radio(asRadio)
} else if let asPodcast = try? container.decode(Podcast.self) {
self = .podcast(asPodcast)
} else {
fatalError("Oops") //Or rather throws a custom error
}
}
}
static func test() {
let mediaJSONStr = #"{"title": "media"}"#
let radioJSONStr = #"{"title": "radio", "channel": 3}"#
let podcastJSONStr = #"{"title": "podcast", "author": "myself"}"#
do {
let decoder = JSONDecoder()
//Create values from JSON
let media = try decoder.decode(Media.self, from: Data(mediaJSONStr.utf8))
print(media)
let radio = try decoder.decode(Radio.self, from: Data(radioJSONStr.utf8))
print(radio)
let podcast = try decoder.decode(Podcast.self, from: Data(podcastJSONStr.utf8))
print(podcast)
let array: [Media] = [radio, podcast]
print(array)
// Encode to Data, that's what's saved into UserDefaults
let encoder = JSONEncoder()
let encodedArray = try encoder.encode(array)
print("Encoded: \(String(data: encodedArray, encoding: .utf8)!)") //It's more readable as JSON String than Data
//This will fail, it's the current author code
let decoded = try decoder.decode([Media].self, from: encodedArray)
print(decoded)
decoded.forEach {
if let asRadio = $0 as? Radio {
print(asRadio)
}else if let asPodcast = $0 as? Podcast {
print(asPodcast)
} else {
print("Nop: \($0)")
}
}
//This is a working solution
let mixedDecoded = try decoder.decode([Mixed].self, from: encodedArray)
let decodedArray: [Media] = mixedDecoded.map {
switch $0 {
case .radio(let radio):
return radio
case .podcast(let podcast):
return podcast
}
}
print(decodedArray)
} catch {
print("Error: \(error)")
}
}
}
SubClassesCodable.test()
推荐阅读
- amazon-cognito - 使用 AWS Cognito 的 Feathersjs 4 oAuth 不起作用
- android - 使用 AWS Amplify Android 检查用户是否已存在?
- android - 将 Expo 应用程序资产中的图像上传到生产服务器
- java - 如何从firebase中检索价值并为其添加价值并在android studio JAVA中更新到firebase
- reactjs - 如何在以太坊交易中使用 useState 设置交易哈希
- algorithm - 优化 2D 网格空间以放置对象
- python - 优化Python中许多子图之间的空间
- flutter - 在颤振中为时间戳添加几小时或几天
- javascript - 有人知道在 Jamboards 中使用 Google Apps 脚本的任何资源吗?
- image - 在颤动中检查图像大小(kb,mb ...)?