Parsing JSON (date) to Swift

Question

I have a return JSON in my application in Swift, and have a field that returns me a date. When I refer to this data, the code gives me something like "/ Date (1420420409680) /". How do I convert this into NSDate? In Swift, please, I´ve tested examples with Objective-C, without success.

Answer 1

That looks very similar to the JSON encoding for a date as used by Microsoft's ASP.NET AJAX, which is described in An Introduction to JavaScript Object Notation (JSON) in JavaScript and .NET:

For example, Microsoft's ASP.NET AJAX uses neither of the described conventions. Rather, it encodes .NET DateTime values as a JSON string, where the content of the string is /Date(ticks)/ and where ticks represents milliseconds since epoch (UTC). So November 29, 1989, 4:55:30 AM, in UTC is encoded as "\/Date(628318530718)\/".

The only difference is that you have the format /Date(ticks)/ and not \/Date(ticks)\/.

You have to extract the number between the parentheses. Dividing that by 1000 gives the number in seconds since 1 January 1970.

The following code shows how that could be done. It is implemented as a "failable convenience initializer" for NSDate:

extension NSDate {
    convenience init?(jsonDate: String) {

        let prefix = "/Date("
        let suffix = ")/"
        // Check for correct format:
        if jsonDate.hasPrefix(prefix) && jsonDate.hasSuffix(suffix) {
            // Extract the number as a string:
            let from = jsonDate.startIndex.advancedBy(prefix.characters.count)
            let to = jsonDate.endIndex.advancedBy(-suffix.characters.count)
            // Convert milliseconds to double
            guard let milliSeconds = Double(jsonDate[from ..< to]) else {
                return nil
            }
            // Create NSDate with this UNIX timestamp
            self.init(timeIntervalSince1970: milliSeconds/1000.0)
        } else {
            return nil
        }
    }
}

Example usage (with your date string):

if let theDate = NSDate(jsonDate: "/Date(1420420409680)/") {
    print(theDate)
} else {
    print("wrong format")
}

This gives the output

2015-01-05 01:13:29 +0000

---

Update for Swift 3 (Xcode 8):

extension Date {
    init?(jsonDate: String) {

        let prefix = "/Date("
        let suffix = ")/"

        // Check for correct format:
        guard jsonDate.hasPrefix(prefix) && jsonDate.hasSuffix(suffix) else { return nil }

        // Extract the number as a string:
        let from = jsonDate.index(jsonDate.startIndex, offsetBy: prefix.characters.count)
        let to = jsonDate.index(jsonDate.endIndex, offsetBy: -suffix.characters.count)

        // Convert milliseconds to double
        guard let milliSeconds = Double(jsonDate[from ..< to]) else { return nil }

        // Create NSDate with this UNIX timestamp
        self.init(timeIntervalSince1970: milliSeconds/1000.0)
    }
}

Example:

if let theDate = Date(jsonDate: "/Date(1420420409680)/") {
    print(theDate)
} else {
    print("wrong format")
}