如何在 Swift 中编码 CGPoint 数组

Question

您好，我从 here 找到了没有数组的好解决方案，可以正常工作

@propertyWrapper
struct EncodablePoint: Encodable {
    var wrappedValue: CGPoint
    enum CodingKeys: CodingKey {
        case x
        case y
    }
    func encode(to encoder: Encoder) throws {
        var c = encoder.container(keyedBy: CodingKeys.self)
        try c.encode(wrappedValue.x, forKey: .x)
        try c.encode(wrappedValue.y, forKey: .y)
    }
}
//usage:
struct Foo: Encodable {
    @EncodablePoint var pt: CGPoint = CGPoint(x: 123, y: 456)
    var other = "zxcv"
}

let foo = Foo()
let encoded = try! JSONEncoder().encode(foo)
print(String(bytes: encoded, encoding: .utf8) ?? "nil") // {"pt":{"x":123,"y":456},"other":"zxcv"}

我想要类似的数组解决方案，如果有人知道请帮助我。 我想要一些类似的东西：

@propertyWrapper
struct EncodablePointsArray: Encodable {
    var wrappedValue: [CGPoint]
    enum CodingKeys: CodingKey {
        ?????
    }
    func encode(to encoder: Encoder) throws {
        ??????
    }
}


struct Foo2: Encodable {
    @EncodablePointsArray var pt: [CGPoint] = [CGPoint]
    var other = "zxcv"
}

let foo2 = Foo2()
let encoded = try! JSONEncoder().encode(foo2)
print(String(bytes: encoded, encoding: .utf8) ?? "nil")
// I wold like output like : {"ArrayPoints“:[{„x“:1.1,“y“:1.2},{„x“:2.1,“y“:3.4}]},"other":"zxcv"}

Answer 1

您正在使用过时的信息。 [CGPoint] 是 Codable 现在没有任何扩展。

struct Foo2: Encodable {
  var pt: [CGPoint] = []
  var other = "zxcv"
}

如果您确实需要包装器，请发布需要它的代码。您的问题表明您不需要包装器。

Answer 2

EncodablePoint 在这里充当CGPoint 的包装器，因此从客户端的角度来看，EncodablePoint 是具有CGPoint 属性的新类型。

如果用作属性包装器，它的作用类似于CGPoint 的数组。但在编码后，它会将其转换为具有x 和y 坐标的自定义对象。

根据你对这样一个对象解码后想要达到的结果，这里有两种选择。

EncodablePoint的编码数组

让我们像这样构建属性包装器

@propertyWrapper
struct EncodablePointArray: Encodable {
    var wrappedValue: [EncodablePoint]
}

那么包装器的客户端应该创建EncodablePoint的实例

struct Points: Encodable {
    @EncodablePointArray var pt: [EncodablePoint] = [
        EncodablePoint(wrappedValue: CGPoint(x: 123, y: 456)),
        EncodablePoint(wrappedValue: CGPoint(x: 789, y: 123)),
        EncodablePoint(wrappedValue: CGPoint(x: 456, y: 789))
    ]
    var other = "zxcv"
}

解码会给你想要的结果

{"pt":{"values":[{"x":123,"y":456},{"x":789,"y":123},{"x":456,"y":789}]},"other":"zxcv"}

但我认为你想使用CGPoint 的数组，所以...

CGPoint的编码数组

如果你想这样直接使用CGPoints

struct Points: Encodable {
    @EncodablePointArray var pt: [CGPoint] = [
        CGPoint(x: 123, y: 456),
        CGPoint(x: 789, y: 123),
        CGPoint(x: 456, y: 789)
    ]
    var other = "zxcv"
}

您必须使用CGPoints 构建您的包装器

@propertyWrapper
struct EncodablePointArray: Encodable {
    var wrappedValue: [CGPoint]
}

但是解码出来的String会不一样：

{"pt":{"values":[[123,456],[789,123],[456,789]]},"other":"zxcv"}

Answer 3

使用unkeyedContainer() 和nestedContainer(keyedBy:) 函数可以解决问题：

@propertyWrapper
struct EncodablePointsArray: Encodable {
    var wrappedValue: [CGPoint]
    
    enum CodingKeys: CodingKey {
        case x
        case y
    }
    
    func encode(to encoder: Encoder) throws {
        var unkeyedContainer = encoder.unkeyedContainer()
        try wrappedValue.forEach {
            var container = unkeyedContainer.nestedContainer(keyedBy: CodingKeys.self)
            try container.encode($0.x, forKey: .x)
            try container.encode($0.y, forKey: .y)
        }
    }
}

以你为例：

struct Foo2: Encodable {
    @EncodablePointsArray var pt: [CGPoint] = [CGPoint(x: 1.1, y: 1.2), CGPoint(x: 2.1, y: 3.4)]
    var other = "zxcv"
}

let foo2 = Foo2()
do {
    let encoded = try JSONEncoder().encode(foo2)
    print(String(bytes: encoded, encoding: .utf8) ?? "nil")
} catch {
    print(error)
}

这将导致：

{
    "pt": [
        {
            "x": 1.1000000000000001,
            "y": 1.2
        },
        {
            "x": 2.1000000000000001,
            "y": 3.3999999999999999
        }
    ],
    "other": "zxcv"
}