How to use Swift's JSONSerialization when JSON returns a single string

问题

So this is likely a very basic question, but I was curious how you would handle parsing a JSON object that returns as a single string using JSONSerialization in Swift. So I'm playing around with a free Harry Potter API and noticed that one of the routes returns a single string (https://www.potterapi.com/v1/sortinghat) and the response it gives is simply a single string of one of the four houses in Harry Potter.

"Ravenclaw"

Below was my attempt.

do {
    let json = try JSONSerialization.jsonObject(with: data, options: []) as? String
    print("json: \(json)")
} catch {
    print("Error: \(error.localizedDescription)")
}

I thought simply typecasting as a String would suffice but I just get the following error: "Error: The data couldn’t be read because it isn’t in the correct format."

I know there are better ways to parse JSON such as using Codable but I am just trying to understand how this would work before moving on to tackling that.

回答1:

JSONSerialization is the wrong tool for this. You want to use JSONDecoder, which is much more useful in Swift:

let json = Data("""
"Ravenclaw"
""".utf8)

let result = try JSONDecoder().decode(String.self, from: json)

Note that this requires iOS 13.1 or macOS 10.15.1. Otherwise you will need to use @vadian's answer.

回答2:

To deserialize a non-collection type you have to set the .allowFragments option

let jsonString = """
"Slytherin"
"""

do {
    if let json = try JSONSerialization.jsonObject(with: Data(jsonString.utf8), options: .allowFragments) as? String {
        print("json: ", json)
    }
} catch {
    print("Error: ", error)
}

JSONDecoder does not work, it calls underlying JSONSerialization with no options.

The sense of deserializing a string to a string is another question, this does the same

if let json = String(data: data, encoding: .utf8) {
    print("json: \(json)")
}

Edit: JSONDecoder does work on iOS 13.1+ and macOS 10.15.1+

来源：https://stackoverflow.com/questions/59236554/how-to-use-swifts-jsonserialization-when-json-returns-a-single-string

标签

json

swift

nsjsonserialization