小编典典

为UIColor实现编码

swift

是否可以实现Encodable和的Decodable属性UIColor

当我尝试添加Decodable扩展名时出现错误

extension UIColor : Decodable {
    public required init(from decoder: Decoder) throws {
        self.init(red: 1, green: 1, blue: 1, alpha: 1)
    }
}

错误:ColorStuff.playground:98:21:错误:初始化程序要求’init(from
:)’只能由required初始化程序在非最终类’UIColor’的定义中满足public必需init(from解码器:Decoder)抛出{

我在这里错过明显的东西吗?

Encodable扩展名没有问题-似乎是个Decodable问题。

该错误消息向我暗示由于无法访问UIColor类定义而无法执行此操作


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2020-07-07

共1个答案

小编典典

由于编译器给出的错误,您不能使扩展UIColor符合Decodable

一种解决方案是创建Codable包装器类型,然后使用它。

由于UIColor已经符合NSCoding,我们只需要编写一个通用类型,就可以对符合的任何内容进行编码和解码NSCoding

import UIKit

struct WrapperOfNSCoding<Wrapped>: Codable where Wrapped: NSCoding {
    var wrapped: Wrapped

    init(_ wrapped: Wrapped) { self.wrapped = wrapped }

    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        let data = try container.decode(Data.self)
        guard let object = NSKeyedUnarchiver.unarchiveObject(with: data) else {
            throw DecodingError.dataCorruptedError(in: container, debugDescription: "failed to unarchive an object")
        }
        guard let wrapped = object as? Wrapped else {
            throw DecodingError.typeMismatch(Wrapped.self, DecodingError.Context(codingPath: container.codingPath, debugDescription: "unarchived object type was \(type(of: object))"))
        }
        self.wrapped = wrapped
    }

    func encode(to encoder: Encoder) throws {
        let data = NSKeyedArchiver.archivedData(withRootObject: wrapped)
        var container = try encoder.singleValueContainer()
        try container.encode(data)
    }
}

let colors = [UIColor.red, UIColor.brown]
print(colors)
let jsonData = try! JSONEncoder().encode(colors.map({ WrapperOfNSCoding($0) }))
let colors2 = try! JSONDecoder().decode([WrapperOfNSCoding<UIColor>].self, from: jsonData).map({ $0.wrapped })
print(colors2)
2020-07-07