编码

Question

我一直在玩Codable并从文件中读取和写入JSON。现在我想编写一个可以读写iOS Coder文件的自定义.strings。谁能帮我这个？我找到了协议Encoder和Decoder，但我不知道我应该在这里实现什么：

class StringsEncoder {}

extension StringsEncoder: Encoder {
    var codingPath: [CodingKey?] {
        return []
    }

    var userInfo: [CodingUserInfoKey : Any] {
        return [:]
    }

    func container<Key>(keyedBy type: Key.Type) -> KeyedEncodingContainer<Key> where Key : CodingKey {

    }

    func unkeyedContainer() -> UnkeyedEncodingContainer {

    }

    func singleValueContainer() -> SingleValueEncodingContainer {

    }
}

extension StringsEncoder: Decoder {
    func container<Key>(keyedBy type: Key.Type) throws -> KeyedDecodingContainer<Key> where Key : CodingKey {

    }

    func unkeyedContainer() throws -> UnkeyedDecodingContainer {

    }

    func singleValueContainer() throws -> SingleValueDecodingContainer {

    }
}

Answer 1

这里的聚会晚了一点，但是鉴于投票数高的问题，我认为这可能对其他人有帮助/启发。（我不会在实践中了解此类代码的实际用途，请为此检查上面的注释。）

不幸的是，鉴于编码堆栈的灵活性和类型安全性，为替代的外部表示形式实现了新的 encoding 和 decoding 解决方案，绝非易事...

编码

让我们开始为所需的strings file外部表示实现 encoding 部分。（必要的类型将以自顶向下的方式引入。）

就像标准JSONEncoder类一样，我们需要引入一个类来公开/驱动我们的新编码API。我们称之为StringsEncoder：

/// An object that encodes instances of a data type 
/// as strings following the simple strings file format.
public class StringsEncoder {

    /// Returns a strings file-encoded representation of the specified value. 
    public func encode<T: Encodable>(_ value: T) throws -> String {
        let stringsEncoding = StringsEncoding()
        try value.encode(to: stringsEncoding)
        return dotStringsFormat(from: stringsEncoding.data.strings)
    }

    private func dotStringsFormat(from strings: [String: String]) -> String {
        var dotStrings = strings.map { "\"\($0)\" = \"\($1)\";" }
        dotStrings.sort()
        dotStrings.insert("/* Generated by StringsEncoder */", at: 0)
        return dotStrings.joined(separator: "\n")
    }
}

接下来，我们需要提供一种符合核心struct协议的类型（例如Encoder）

fileprivate struct StringsEncoding: Encoder {

    /// Stores the actual strings file data during encoding.
    fileprivate final class Data {
        private(set) var strings: [String: String] = [:]

        func encode(key codingKey: [CodingKey], value: String) {
            let key = codingKey.map { $0.stringValue }.joined(separator: ".")
            strings[key] = value
        }
    }

    fileprivate var data: Data

    init(to encodedData: Data = Data()) {
        self.data = encodedData
    }

    var codingPath: [CodingKey] = []

    let userInfo: [CodingUserInfoKey : Any] = [:]

    func container<Key: CodingKey>(keyedBy type: Key.Type) -> KeyedEncodingContainer<Key> {
        var container = StringsKeyedEncoding<Key>(to: data)
        container.codingPath = codingPath
        return KeyedEncodingContainer(container)
    }

    func unkeyedContainer() -> UnkeyedEncodingContainer {
        var container = StringsUnkeyedEncoding(to: data)
        container.codingPath = codingPath
        return container
   }

    func singleValueContainer() -> SingleValueEncodingContainer {
        var container = StringsSingleValueEncoding(to: data)
        container.codingPath = codingPath
        return container
    }
}

最后，我们需要处理所有3种编码容器类型：

KeyedEncodingContainer
UnkeyedEncodingContainer
SingleValueEncodingContainer

fileprivate struct StringsKeyedEncoding<Key: CodingKey>: KeyedEncodingContainerProtocol {

    private let data: StringsEncoding.Data

    init(to data: StringsEncoding.Data) {
        self.data = data
    }

    var codingPath: [CodingKey] = []

    mutating func encodeNil(forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: "nil")
    }

    mutating func encode(_ value: Bool, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }

    mutating func encode(_ value: String, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value)
    }

    mutating func encode(_ value: Double, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }

    mutating func encode(_ value: Float, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }

    mutating func encode(_ value: Int, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }

    mutating func encode(_ value: Int8, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }

    mutating func encode(_ value: Int16, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }

    mutating func encode(_ value: Int32, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }

    mutating func encode(_ value: Int64, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }

    mutating func encode(_ value: UInt, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }

    mutating func encode(_ value: UInt8, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }

    mutating func encode(_ value: UInt16, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }

    mutating func encode(_ value: UInt32, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }

    mutating func encode(_ value: UInt64, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }

    mutating func encode<T: Encodable>(_ value: T, forKey key: Key) throws {
        var stringsEncoding = StringsEncoding(to: data)
        stringsEncoding.codingPath.append(key)
        try value.encode(to: stringsEncoding)
    }

    mutating func nestedContainer<NestedKey: CodingKey>(
        keyedBy keyType: NestedKey.Type,
        forKey key: Key) -> KeyedEncodingContainer<NestedKey> {
        var container = StringsKeyedEncoding<NestedKey>(to: data)
        container.codingPath = codingPath + [key]
        return KeyedEncodingContainer(container)
    }

    mutating func nestedUnkeyedContainer(forKey key: Key) -> UnkeyedEncodingContainer {
        var container = StringsUnkeyedEncoding(to: data)
        container.codingPath = codingPath + [key]
        return container
    }

    mutating func superEncoder() -> Encoder {
        let superKey = Key(stringValue: "super")!
        return superEncoder(forKey: superKey)
    }

    mutating func superEncoder(forKey key: Key) -> Encoder {
        var stringsEncoding = StringsEncoding(to: data)
        stringsEncoding.codingPath = codingPath + [key]
        return stringsEncoding
    }
}

fileprivate struct StringsUnkeyedEncoding: UnkeyedEncodingContainer {

    private let data: StringsEncoding.Data

    init(to data: StringsEncoding.Data) {
        self.data = data
    }

    var codingPath: [CodingKey] = []

    private(set) var count: Int = 0

    private mutating func nextIndexedKey() -> CodingKey {
        let nextCodingKey = IndexedCodingKey(intValue: count)!
        count += 1
        return nextCodingKey
    }

    private struct IndexedCodingKey: CodingKey {
        let intValue: Int?
        let stringValue: String

        init?(intValue: Int) {
            self.intValue = intValue
            self.stringValue = intValue.description
        }

        init?(stringValue: String) {
            return nil
        }
    }

    mutating func encodeNil() throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: "nil")
    }

    mutating func encode(_ value: Bool) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }

    mutating func encode(_ value: String) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value)
    }

    mutating func encode(_ value: Double) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }

    mutating func encode(_ value: Float) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }

    mutating func encode(_ value: Int) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }

    mutating func encode(_ value: Int8) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }

    mutating func encode(_ value: Int16) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }

    mutating func encode(_ value: Int32) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }

    mutating func encode(_ value: Int64) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }

    mutating func encode(_ value: UInt) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }

    mutating func encode(_ value: UInt8) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }

    mutating func encode(_ value: UInt16) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }

    mutating func encode(_ value: UInt32) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }

    mutating func encode(_ value: UInt64) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }

    mutating func encode<T: Encodable>(_ value: T) throws {
        var stringsEncoding = StringsEncoding(to: data)
        stringsEncoding.codingPath = codingPath + [nextIndexedKey()]
        try value.encode(to: stringsEncoding)
    }

    mutating func nestedContainer<NestedKey: CodingKey>(
        keyedBy keyType: NestedKey.Type) -> KeyedEncodingContainer<NestedKey> {
        var container = StringsKeyedEncoding<NestedKey>(to: data)
        container.codingPath = codingPath + [nextIndexedKey()]
        return KeyedEncodingContainer(container)
    }

    mutating func nestedUnkeyedContainer() -> UnkeyedEncodingContainer {
        var container = StringsUnkeyedEncoding(to: data)
        container.codingPath = codingPath + [nextIndexedKey()]
        return container
    }

    mutating func superEncoder() -> Encoder {
        var stringsEncoding = StringsEncoding(to: data)
        stringsEncoding.codingPath.append(nextIndexedKey())
        return stringsEncoding
    }
}

fileprivate struct StringsSingleValueEncoding: SingleValueEncodingContainer {

    private let data: StringsEncoding.Data

    init(to data: StringsEncoding.Data) {
        self.data = data
    }

    var codingPath: [CodingKey] = []

    mutating func encodeNil() throws {
        data.encode(key: codingPath, value: "nil")
    }

    mutating func encode(_ value: Bool) throws {
        data.encode(key: codingPath, value: value.description)
    }

    mutating func encode(_ value: String) throws {
        data.encode(key: codingPath, value: value)
    }

    mutating func encode(_ value: Double) throws {
        data.encode(key: codingPath, value: value.description)
    }

    mutating func encode(_ value: Float) throws {
        data.encode(key: codingPath, value: value.description)
    }

    mutating func encode(_ value: Int) throws {
        data.encode(key: codingPath, value: value.description)
    }

    mutating func encode(_ value: Int8) throws {
        data.encode(key: codingPath, value: value.description)
    }

    mutating func encode(_ value: Int16) throws {
        data.encode(key: codingPath, value: value.description)
    }

    mutating func encode(_ value: Int32) throws {
        data.encode(key: codingPath, value: value.description)
    }

    mutating func encode(_ value: Int64) throws {
        data.encode(key: codingPath, value: value.description)
    }

    mutating func encode(_ value: UInt) throws {
        data.encode(key: codingPath, value: value.description)
    }

    mutating func encode(_ value: UInt8) throws {
        data.encode(key: codingPath, value: value.description)
    }

    mutating func encode(_ value: UInt16) throws {
        data.encode(key: codingPath, value: value.description)
    }

    mutating func encode(_ value: UInt32) throws {
        data.encode(key: codingPath, value: value.description)
    }

    mutating func encode(_ value: UInt64) throws {
        data.encode(key: codingPath, value: value.description)
    }

    mutating func encode<T: Encodable>(_ value: T) throws {
        var stringsEncoding = StringsEncoding(to: data)
        stringsEncoding.codingPath = codingPath
        try value.encode(to: stringsEncoding)
    }
}

很明显，我就如何使用（非常！）简单的 strings文件格式编码嵌套类型做出了一些设计决策。希望我的代码很清楚，如果需要的话，应该很容易调整编码细节。

测试

一个简单的Codable类型的简单测试：

struct Product: Codable {
    var name: String
    var price: Float
    var info: String
}

let iPhone = Product(name: "iPhone X", price: 1_000, info: "Our best iPhone yet!")

let stringsEncoder = StringsEncoder()
do {
    let stringsFile = try stringsEncoder.encode(iPhone)
    print(stringsFile)
} catch {
    print("Encoding failed: \(error)")
}

输出：

/* Generated by StringsEncoder */
"info" = "Our best iPhone yet!";
"name" = "iPhone X";
"price" = "1000.0";

使用嵌套结构和数组的更复杂的测试：

struct Product: Codable {
    var name: String
    var price: Float
    var info: String
}

struct Address: Codable {
    var street: String
    var city: String
    var state: String
}

struct Store: Codable {
    var name: String
    var address: Address // nested struct
    var products: [Product] // array
}

let iPhone = Product(name: "iPhone X", price: 1_000, info: "Our best iPhone yet!")
let macBook = Product(name: "Mac Book Pro", price: 2_000, info: "Early 2019")
let watch = Product(name: "Apple Watch", price: 500, info: "Series 4")

let appleStore = Store(
    name: "Apple Store",
    address: Address(street: "300 Post Street", city: "San Francisco", state: "CA"),
    products: [iPhone, macBook, watch]
)

let stringsEncoder = StringsEncoder()
do {
    let stringsFile = try stringsEncoder.encode(appleStore)
    print(stringsFile)
} catch {
    print("Encoding failed: \(error)")
}

输出：

/* Generated by StringsEncoder */
"address.city" = "San Francisco";
"address.state" = "CA";
"address.street" = "300 Post Street";
"name" = "Apple Store";
"products.0.info" = "Our best iPhone yet!";
"products.0.name" = "iPhone X";
"products.0.price" = "1000.0";
"products.1.info" = "Early 2019";
"products.1.name" = "Mac Book Pro";
"products.1.price" = "2000.0";
"products.2.info" = "Series 4";
"products.2.name" = "Apple Watch";
"products.2.price" = "500.0";

解码

鉴于这个答案已经有多大了，我将离开解码部分（即，创建StringsDecoder类，符合Decoder协议等）作为对读者的练习...请让我知道你们是否需要任何帮助；）

Swift：自定义编码器/解码器到字符串资源格式

1 个答案:

编码

测试

解码