swift4 - 使 UIColor 可编码

Question

struct Task: Codable {
    var content: String
    var deadline: Date
    var color: UIColor
...
}

有警告说“类型'Task'不符合协议(protocol)'Decodable'”和“类型'Task'不符合协议(protocol)'Encodable'”。查了一下发现这是因为UIColor不符合Codable。但我不知道如何解决这个问题。所以...

如何使 UIColor 可编码？

Answer 1

如果您只关心 4 个颜色组件，这是一个使用包装器结构的简单解决方案

struct Color : Codable {
    var red : CGFloat = 0.0, green: CGFloat = 0.0, blue: CGFloat = 0.0, alpha: CGFloat = 0.0
    
    var uiColor : UIColor {
        return UIColor(red: red, green: green, blue: blue, alpha: alpha)
    }
    
    init(uiColor : UIColor) {
        uiColor.getRed(&red, green: &green, blue: &blue, alpha: &alpha)
    }
}

在这种情况下，您必须编写一个自定义初始化程序来转换 Color 中的 4 个颜色分量。至 UIColor反之亦然。

struct Task: Codable {
    
    private enum CodingKeys: String, CodingKey { case content, deadline, color }
    
    var content: String
    var deadline: Date
    var color : UIColor
    
    init(content: String, deadline: Date, color : UIColor) {
        self.content = content
        self.deadline = deadline
        self.color = color
    }
    
   init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        content = try container.decode(String.self, forKey: .content)
        deadline = try container.decode(Date.self, forKey: .deadline)
        color = try container.decode(Color.self, forKey: .color).uiColor
    }
    
    public func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(content, forKey: .content)
        try container.encode(deadline, forKey: .deadline)
        try container.encode(Color(uiColor: color), forKey: .color)
    }
}

现在您可以编码和解码 UIColor

let task = Task(content: "Foo", deadline: Date(), color: .orange)
do {
    let data = try JSONEncoder().encode(task)
    print(String(data: data, encoding: .utf8)!)
    let newTask = try JSONDecoder().decode(Task.self, from: data)
    print(newTask)
} catch {  print(error) }

Swift 5.1 及更高版本的智能替代方案是属性包装器

@propertyWrapper
struct CodableColor {
    var wrappedValue: UIColor
}

extension CodableColor: Codable {
    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        let data = try container.decode(Data.self)
        guard let color = try NSKeyedUnarchiver.unarchivedObject(ofClass: UIColor.self, from: data) else {
            throw DecodingError.dataCorruptedError(
                in: container,
                debugDescription: "Invalid color"
            )
        }
        wrappedValue = color
    }

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

并用 @CodableColor 标记该属性

struct Task: Codable {
    var content: String
    var deadline: Date
    @CodableColor var color: UIColor
...
}