Swift 4: 结构中的结构

Question

我在创建结构时遇到问题。

我的结构：

public struct Device: Codable {
    let data: DeviceData
    let meta: Meta?
}

public struct DeviceData: Codable {
    let deviceID: String?
    let type: String?
    let attributes: Attributes?

    private enum CodingKeys: String, CodingKey {
        case deviceID = "id"
        case type
        case attributes
    }
}

public struct Attributes: Codable {
    let name: String?
    let asdf: String?
    let payload: Payload?
}

public struct Payload: Codable {
    let example: String?
}

public struct Meta: Codable {
    let currentPage: Int?
    let nextPage: Int?
    let deviceID: [String]?
}

当我现在想创建此结构的元素时：

var exampleData = Device(
        data: DeviceData(
            type: "messages",
            attributes: Attributes(
                name: "Hello World",
                asdf: "This is my message",
                payload: Payload(
                    example: "World"
                )
            )
        ),
        meta: Meta(
            deviceID: ["asfd-asdf-asdf-asdf-asdfcasdf"]
        )
    )

我会得到一个错误。无法详细说明此错误，因为当我删除 "meta" 元素时，因为它是可选的，所以会发生另一个错误...此特定代码的错误消息是：

Extra argument 'meta' in call

希望有人能帮助我。

Answer 1

您忘记了调用 DeviceData.init(deviceID:type:attributes:) 的 deviceID: 命名参数，并且还忘记了 Meta.init(currentPage:nextPage:deviceID) 的 currentPage 和 nextPage 命名参数。

这是一个编译示例：

var exampleData = Device(
    data: DeviceData(
        deviceID: "someID",
        type: "messages",
        attributes: Attributes(
            name: "Hello World",
            asdf: "This is my message",
            payload: Payload(
                example: "World"
            )
        )
    ),
    meta: Meta(
        currentPage: 123,
        nextPage: 456,
        deviceID: ["asfd-asdf-asdf-asdf-asdfcasdf"]
    )
)

Answer 2

您省略了 DeviceData 和 Meta 初始值设定项的参数。在对您提出的另一个答案的评论中：

do I have to add them and set them to nil, even if they are optional? maybe that's my problem!

你可以这样做，例如类似于：

meta: Meta(currentPage: nil,
           nextPage: nil,
           deviceID: ["asfd-asdf-asdf-asdf-asdfcasdf"]
          )

或者，您可以编写自己的初始化器而不是依赖默认的成员初始化器，并在那里提供默认值而不是在每次调用时提供默认值，例如类似于：

init(currentPage : Int? = nil, nextPage : Int? = nil, deviceID : [String]? = nil)
{
   self.currentPage = currentPage
   self.nextPage = nextPage
   self.deviceID = deviceID
}

您原来的调用（省略了 currentPage 和 nextPage）将有效并将这两个设置为 nil。

HTH

Swift 4: 结构中的结构

Swift 4: struct in struct

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swift4

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