Swift 4 Decodable-其他变量 [英] Swift 4 Decodable - Additional Variables

问题描述

到目前为止，我还没有发现或可以在线找到的东西.

Something I havent figured out or have been able to find online as of yet.

是否可以将其他字段添加到包含可解码协议的结构中，而JSON数据中不存在该字段?

Is there a way to add additional fields onto a struct containing the decodable protocol in which are not present in the JSON Data?

例如，为了简单起见，我有一个这样构造的json对象数组

For example and simplicity, say I have an array of json objects structured as such

{ "name":"name1"， "url":"www.google.com/randomImage" }

{ "name": "name1", "url": "www.google.com/randomImage" }

但是说我想向包含可解码的结构(例如，

but say I want to add a UIImage variable to that struct containing the decodable such as

struct Example1: Decodable {
    var name: String?
    var url: String?
    var urlImage: UIImage? //To add later
}

是否有一种方法可以实现可解码协议，以便从JSON获取名称和网址，但允许我稍后添加UIImage?

Is there a way to implement the decodable protocol in order to get the name and url from the JSON but allow me to add the UIImage later?

推荐答案

要排除urlImage，您必须手动遵循Decodable，而不是合成其要求:

To exclude urlImage you must manually conform to Decodable instead of letting its requirements be synthesized:

struct Example1 : Decodable { //(types should be capitalized)
    var name: String?
    var url: URL? //try the `URL` type! it's codable and much better than `String` for storing URLs
    var urlImage: UIImage? //not decoded

    private enum CodingKeys: String, CodingKey { case name, url } //this is usually synthesized, but we have to define it ourselves to exclude `urlImage`
}

在Swift 4.1之前，这仅在将= nil添加到urlImage时才有效，即使通常将nil的默认值假定为可选属性.

Before Swift 4.1 this only works if you add = nil to urlImage, even though the default value of nil is usually assumed for optional properties.

如果要在初始化时为urlImage提供值，而不是使用= nil，则还可以手动定义初始化程序:

If you want to provide a value for urlImage at initialization, rather than using = nil, you can also manually define the initializer:

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        name = try container.decode(String.self, forKey: .name)
        url = try container.decode(URL.self, forKey: .url)
        urlImage = //whatever you want!
    }

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