Swift Codable - 如何对自定义数组进行编码

Question

这是我的JSON案例

{
"image_id" : 11101,
"image_source_id" : 9,
"image_author" : "",
"image_copyright" : "",
"image_format_list" : [
{
"image_format" : {
"image_url" : "https://static.musixmatch.com/images-storage/mxmimages/1/0/1/1/1/11101_2.jpg",
"image_format_id" : 2,
"width" : 150,
"height" : 150
}
},
{
"image_format" : {
"image_url" : "https://static.musixmatch.com/images-storage/mxmimages/1/0/1/1/1/11101_16.jpg",
"image_format_id" : 16,
"width" : 451,
"height" : 500
}
}
]
}

我在两个不同的类中正确解码了我的自定义对象：MXMImage 和 MXMImageFormat。 但是我不知道如何重新编码我的对象以重建相同的JSON

这是我的代码：

struct MXMImage : Codable, Equatable {
let imageId: Int
let imageSourceId: Int
let imageAuthor: String?
let imageCopyright: String?
let imageFormatList: [MXMImageFormat]?

enum CodingKeys: String, Swift.CodingKey {
case imageId
case imageSourceId
case imageAuthor
case imageCopyright
case imageFormatList

enum ImageFormatListKey: String, CodingKey {
case imageFormat
}
}

public init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
imageId = try (container.decodeIfPresent(Int.self, forKey: .imageId) ?? 0)
imageSourceId = try (container.decodeIfPresent(Int.self, forKey: .imageSourceId) ?? 0)
imageAuthor = try? container.decodeIfPresent(String.self, forKey: .imageAuthor)
imageCopyright = try? container.decodeIfPresent(String.self, forKey: .imageCopyright)

var imagesFormatListContainer = try container.nestedUnkeyedContainer(forKey: .imageFormatList)
var imagesList:[MXMImageFormat] = []
while !imagesFormatListContainer.isAtEnd {
let imageFormatContainer = try imagesFormatListContainer.nestedContainer(keyedBy: CodingKeys.ImageFormatListKey.self)
let imageFormat = try? imageFormatContainer.decode(MXMImageFormat.self, forKey: .imageFormat)
if let imageFormat = imageFormat {
imagesList.append(imageFormat)
}
}
self.imageFormatList = imagesList
}

public func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)

try container.encodeIfPresent(imageId, forKey: .imageId)
try container.encodeIfPresent(imageSourceId, forKey: .imageSourceId)
try container.encodeIfPresent(imageAuthor, forKey: .imageAuthor)
try container.encodeIfPresent(imageCopyright, forKey: .imageCopyright)

var imageContainer = container.nestedUnkeyedContainer(forKey: .imageFormatList)
try imageFormatList?.forEach { imgFormat in
var nested = imageContainer.nestedContainer(keyedBy: CodingKeys.ImageFormatListKey.self)
let data = try imgFormat.encoded()
try nested.encode(data, forKey: .imageFormat)
}
}
}

特别是，我不知道如何在键image_format中重新缩进我的MXMImageFormat对象，然后对自定义数组进行编码。有可能做到吗？提前致谢

Answer 1

而不是nestedContainers您可以解码/编码[[String:MXMImageFormat]]数组并映射它

struct MXMImage : Codable, Equatable {
let imageId: Int
let imageSourceId: Int
let imageAuthor: String?
let imageCopyright: String?
let imageFormatList: [MXMImageFormat]?
private enum CodingKeys : String, CodingKey { case imageId,  imageSourceId,  imageAuthor, imageCopyright, imageFormatList}
public init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
imageId = try container.decode(Int.self, forKey: .imageId)
imageSourceId = try container.decode(Int.self, forKey: .imageSourceId)
imageAuthor = try container.decodeIfPresent(String.self, forKey: .imageAuthor)
imageCopyright = try container.decodeIfPresent(String.self, forKey: .imageCopyright)
if let imageFormatListData = try container.decodeIfPresent([[String:MXMImageFormat]].self, forKey: .imageFormatList) {
imageFormatList = imageFormatListData.compactMap{$0["image_format"]}
} else {
imageFormatList = nil
}
}
public func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(imageId, forKey: .imageId)
try container.encode(imageSourceId, forKey: .imageSourceId)
try container.encodeIfPresent(imageAuthor, forKey: .imageAuthor)
try container.encodeIfPresent(imageCopyright, forKey: .imageCopyright)
if let imageFormatListData = imageFormatList {
try container.encode(imageFormatListData.map{["image_format":$0]}, forKey: .imageFormatList)
}
}
}
struct MXMImageFormat : Codable, Equatable {
let imageUrl : URL
let imageFormatId, width, height : Int
}

Answer 2

假设MXMImageFormat是这样的：

struct MXMImageFormat : Codable {
let imageUrl: String
let imageFormatId: Int
let width: Int
let height: Int
}

我认为你想多了。你可以做：

try imageFormatList?.forEach { imgFormat in
var nested = imageContainer.nestedContainer(keyedBy: CodingKeys.ImageFormatListKey.self)
try nested.encode(imgFormat, forKey: .imageFormat)
}

由于encode接受任何Encodable，包括imgFormat。您实际上不需要先转换为Data(至少这就是您似乎试图这样做的原因(。

一些测试代码：

let json = """
{
"image_id": 11101,
"image_source_id": 9,
"image_author": "",
"image_copyright": "",
"image_format_list": [{
"image_format": {
"image_url": "https://static.musixmatch.com/images-storage/mxmimages/1/0/1/1/1/11101_2.jpg",
"image_format_id": 2,
"width": 150,
"height": 150
}
},
{
"image_format": {
"image_url": "https://static.musixmatch.com/images-storage/mxmimages/1/0/1/1/1/11101_16.jpg",
"image_format_id": 16,
"width": 451,
"height": 500
}
}
]
}
""".data(using: .utf8)!
let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase
let model = try! decoder.decode(MXMImage.self, from: json)
let encoder = JSONEncoder()
encoder.keyEncodingStrategy = .convertToSnakeCase
let string = String(data: try! encoder.encode(model), encoding: .utf8)!
print(string) // this should be the same JSON as the one in the string literal

另请注意，在encode中，您不必在此处使用try?：

while !imagesFormatListContainer.isAtEnd {
let imageFormatContainer = try imagesFormatListContainer.nestedContainer(keyedBy: CodingKeys.ImageFormatListKey.self)
// here vvvvvvv
let imageFormat = try? imageFormatContainer.decode(MXMImageFormat.self, forKey: .imageFormat)
if let imageFormat = imageFormat {
imagesList.append(imageFormat)
}
}