如何处理 JSON 格式与 Swift 4 Codable 的不一致?
How to handle JSON format inconsistencies with Swift 4 Codable?
我需要解析 JSON 其中一个字段值是数组:
"list" :
[
{
"value" : 1
}
]
或一个空字符串,以防没有数据:
"list" : ""
不好,但我无法更改格式。
我正在考虑将我的手动解析转换为 JSONDecoder
和 Codable
struct
。
我该如何处理这种讨厌的不一致?
你需要尝试用一种方式解码,如果失败,再用另一种方式解码。这意味着您不能使用 compiler-generated 解码支持。你必须手工完成。如果你想要完整的错误检查,这样做:
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
}
}
如果你不想检查错误,你可以将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: [])
我需要解析 JSON 其中一个字段值是数组:
"list" :
[
{
"value" : 1
}
]
或一个空字符串,以防没有数据:
"list" : ""
不好,但我无法更改格式。
我正在考虑将我的手动解析转换为 JSONDecoder
和 Codable
struct
。
我该如何处理这种讨厌的不一致?
你需要尝试用一种方式解码,如果失败,再用另一种方式解码。这意味着您不能使用 compiler-generated 解码支持。你必须手工完成。如果你想要完整的错误检查,这样做:
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
}
}
如果你不想检查错误,你可以将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: [])