我需要解析其中一个字段值是数组的JSON:

"list" :
[
    {
        "value" : 1
    }
]

或一个空字符串,以防没有数据:
"list" : ""

不好,但是我不能更改格式。

我正在考虑将我的手动解析(这很容易)转换为JSONDecoderCodable struct

我该如何处理这种令人讨厌的不一致?

最佳答案

您需要尝试以一种方式对其进行解码,如果失败,则以另一种方式进行解码。这意味着您不能使用编译器生成的解码支持。你必须手工做。如果要进行全面的错误检查,请执行以下操作:

import Foundation

struct ListItem: Decodable {
    var value: Int
}

struct MyResponse: Decodable {

    var list: [ListItem] = []

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        do {
            list = try container.decode([ListItem].self, forKey: .list)
        } catch {
            switch error {
            // In Swift 4, the expected type is [Any].self, but I think it will be [ListItem].self in a newer Swift with conditional conformance support.
            case DecodingError.typeMismatch(let expectedType, _) where expectedType == [Any].self || expectedType == [ListItem].self:
                let dummyString = try container.decode(String.self, forKey: .list)
                if dummyString != "" {
                    throw DecodingError.dataCorruptedError(forKey: .list, in: container, debugDescription: "Expected empty string but got \"\(dummyString)\"")
                }
                list = []
            default: throw error
            }
        }
    }

    enum CodingKeys: String, CodingKey {
        case list
    }

}

如果您不希望进行错误检查,则可以将init(from:)缩短为:
    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        list = (try? container.decode([ListItem].self, forKey: .list)) ?? []
    }

测试1:
let jsonString1 = """
{
    "list" : [ { "value" : 1 } ]
}
"""
print(try! JSONDecoder().decode(MyResponse.self, from: jsonString1.data(using: .utf8)!))

输出1:
MyResponse(list: [__lldb_expr_82.ListItem(value: 1)])

测试2:
let jsonString2 = """
{
    "list" : ""
}
"""
print(try! JSONDecoder().decode(MyResponse.self, from: jsonString2.data(using: .utf8)!))

输出2:
MyResponse(list: [])

09-25 17:07