如何处理解码对象时不存在枚举值的情况?例如,我将如何处理可怕的情况"是以下示例中的评级类型?如果没有值存在,有没有办法设置默认值?
public struct Review: Decodable {
public var ratingType: RatingType?
enum CodingKeys: String, CodingKey {
case ratingType = "rating_type"
}
public init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
ratingType = try container.decodeIfPresent(RatingType.self, forKey: .ratingType)
}
}
public enum RatingType: String, Codable {
case Good = "good"
case Bad = "bad"
}
答案 0 :(得分:1)
nil
将返回try?
,如果值无效,则可能会抛出错误。使用ratingType =
(try? (container.decodeIfPresent(RatingType.self, forKey: .ratingType) ?? <some default value>)
) ?? <some default value>
,我们可以这样做:
private void button3_Click(object sender, EventArgs e)
{
double val = double.Parse(textBox1.Text);
while (val != 0)
{
val--;
}
textBox1.Text = val.ToString();
}
答案 1 :(得分:1)
如果应该实际使用收到的意外评级(针对客户端和服务器之间版本不匹配的防御性编码或其他),您可以尝试使用不同的枚举定义:
enum RatingType
{
case good
case bad
case other(String)
}
您失去了自动编码功能,但却获得了灵活性。
可能的实施:
import Foundation
struct Review
{
public var rating: RatingType?
enum CodingKeys: String, CodingKey {
case rating = "rating_type"
}
public init(rating: RatingType) {
self.rating = rating
}
}
extension Review: Decodable
{
public init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
if let label = try container.decodeIfPresent(String.self, forKey: .rating) {
rating = RatingType(label: label)
}
}
}
extension Review: Encodable
{
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
if let rating = rating {
try container.encode(rating.label, forKey: .rating)
}
}
}
enum RatingType
{
case good
case bad
case other(String)
init(label: String) {
switch label {
case "good": self = .good
case "bad": self = .bad
default: self = .other(label)
}
}
var label: String {
switch self {
case .bad: return "bad"
case .good: return "good"
case let .other(label): return label
}
}
}
在现实生活中,您可能希望RatingType
符合Codable
/ Decodable
,从而简化编码/编码。随意修改。
执行编码/解码的示例:
func encode_review(_ review: Review) throws -> String
{
let data = try JSONEncoder().encode(review)
return String(data: data, encoding: String.Encoding.utf8) ?? "/* ERROR */"
}
func decode_json(_ json: String) throws -> Review?
{
guard let data = json.data(using: String.Encoding.utf8) else { return nil }
let review = try JSONDecoder().decode(Review.self, from: data)
return review
}
print(try! encode_review(Review(rating: .good))) // {"rating_type":"good"}
print(try! encode_review(Review(rating: .other("horrible")))) // {"rating_type":"horrible"}
let good_review_json = """
{"rating_type":"good"}
"""
let great_review_json = """
{"rating_type":"great"}
"""
if let review = try! decode_json(good_review_json), let label = review.rating?.label {
print(label) // good
}
if let review = try! decode_json(great_review_json), let label = review.rating?.label {
print(label) // great
}