[英]How to handle JSON format inconsistencies with Swift 4 Codable?
I need to parse JSON of which one of the field value is either an array: 我需要解析其中一个字段值是数组的JSON:
"list" :
[
{
"value" : 1
}
]
or an empty string, in case there's no data: 或一个空字符串,以防没有数据:
"list" : ""
Not nice, but I can't change the format. 不好,但是我不能更改格式。
I'm looking at converting my manual parsing, for which this was easy, to JSONDecoder
and Codable
struct
's. 我正在考虑将我的手动解析(这很容易)转换为
JSONDecoder
和Codable
struct
。
How can I handle this nasty inconsistency? 我该如何处理这种令人讨厌的不一致?
You need to try decoding it one way, and if that fails, decode it the other way. 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。 This means you can't use the compiler-generated decoding support.
这意味着您不能使用编译器生成的解码支持。 You have to do it by hand.
您必须手动完成。 If you want full error checking, do it like this:
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
}
}
If you want no error checking, you can shorten init(from:)
to this: 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)) ?? []
}
Test 1: 测试1:
let jsonString1 = """
{
"list" : [ { "value" : 1 } ]
}
"""
print(try! JSONDecoder().decode(MyResponse.self, from: jsonString1.data(using: .utf8)!))
Output 1: 输出1:
MyResponse(list: [__lldb_expr_82.ListItem(value: 1)])
Test 2: 测试2:
let jsonString2 = """
{
"list" : ""
}
"""
print(try! JSONDecoder().decode(MyResponse.self, from: jsonString2.data(using: .utf8)!))
Output 2: 输出2:
MyResponse(list: [])
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