如何在JSONDecoder中处理空日期字符串

Question

The date parameter in my json can be empty(""). How to handle it in JSONDecoder?

The custom dateDecodingStrategy can only handle different format, but can't handle an empty value.(The date which formatter returned can't be optional).

When the date have an value, it will work perfectly. But when the date is "", it will crash.

decoder.dateDecodingStrategy = .custom({ (decoder) -> Date in
        let container = try decoder.singleValueContainer()
        let dateStr = try container.decode(String.self)

        let formatter = DateFormatter()
        formatter.calendar = Calendar(identifier: .iso8601)
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.timeZone = TimeZone(secondsFromGMT: 0)
        formatter.dateFormat = "yyyy"
        if let date = formatter.date(from: dateStr) {
            return date
        }
        formatter.dateFormat = "yyyy-MM-dd"
        if let date = formatter.date(from: dateStr) {
            return date
        }
        throw DateError.invalidDate
    })

Answer 1

Based on @vadian's comment, and supposing you are expecting user related data with a date of birth (dob) that may or may not have been declared by a certain user, what I did was the following

public init(from decoder: Decoder) throws {
    //init other properties...
    do {
        self.dob = try container.decode(Date.self, forKey: .dob)
    } catch {
        self.dob = nil
    }
}

But again as per @vadian's comment, it would be better if the dob wasn't returned in the JSON response. That way you wouldn't need the do/catch blocks at all.