编码通用String对象给出nil Swift

Question

I have a UserDefaults class that handles storing, deleting, and fetching of stored objects to defaults. Here's the complete class, neat and simple, I believe:

Now the problem lies in storing function. I couldn't seem to encode an Encodable String object. I know I could just store that object to the defaults, but that would defeat the purpose of this MVDefaults that deals with generic objects.

Anything I'm missing here?

import Foundation

enum MVDefaultsKey: String {
    case requestToken = "defaultsRequestToken"
}

/// The class that has multiple class functions for handling defaults.
/// Also has the helper class functions for handling auth tokens.
class MVDefaults {

    // MARK: - Functions

    /// Stores token.
    class func store<T: Encodable>(_ object: T, key: MVDefaultsKey) {
        let encoder = JSONEncoder()
        let encoded = try? encoder.encode(object)
        UserDefaults.standard.set(encoded, forKey: key.rawValue)
    }

    /// Removes the stored token
    class func removeDefaultsWithKey(_ key: MVDefaultsKey) {
        UserDefaults.standard.removeObject(forKey: key.rawValue)
    }

    /// Returns stored token (optional) if any.
    class func getObjectWithKey<T: Decodable>(_ key: MVDefaultsKey, type: T.Type) -> T? {
        guard let savedData = UserDefaults.standard.data(forKey: key.rawValue) else {
            return nil
        }

        let object = try? JSONDecoder().decode(type, from: savedData)

        return object
    }
}

Answer 1

Think about what would the string "hello" encoded to JSON, look like. It would just look like:

"hello"

wouldn't it?

That is not a valid JSON (according to here )! You can't encode a string directly to JSON, and you can't decode a string directly either.

For example, this code

let string = try! JSONDecoder().decode(String.self, from: "\"hello\"".data(using: .utf8)!)

will produce the error

JSON text did not start with array or object and option to allow fragments not set.

And

let data = try! JSONEncoder().encode("Hello")

will produce the error:

Top-level String encoded as string JSON fragment.

The work around here is just to store your strings with the dedicated set methods provided by UserDefaults . You can still have your generic method, though, you just need to check the type and cast:

if let str = object as? String {
    UserDefaults.standard.set(str, forKey: key)
} else if let int = object as? Int {
    ...

Answer 2

Whilst Sweeper's comment is helpful and should be the answer (since I won't be able to come up to my own answer without his), I'll still go ahead and share what I did to my Defaults class, to make it handle the non JSON encoding objects (eg String, Int, Array, and whatnot).

Here it is:

MVDefaults.swift

import Foundation

enum MVDefaultsKey: String {
    case requestToken = "defaultsRequestToken"
    case someOtherKey = "defaultsKeyForTests"
}

/// The class that has multiple class functions for handling defaults.
/// Also has the helper class functions for handling auth tokens.
class MVDefaults {

    // MARK: - Functions

    /// Stores object.
    class func store<T: Encodable>(_ object: T, key: MVDefaultsKey) {
        let encoder = JSONEncoder()
        let encoded = try? encoder.encode(object)

        if encoded == nil {
            UserDefaults.standard.set(object, forKey: key.rawValue)
            return
        }

        UserDefaults.standard.set(encoded, forKey: key.rawValue)
    }

    /// Removes the stored object
    class func removeDefaultsWithKey(_ key: MVDefaultsKey) {
        UserDefaults.standard.removeObject(forKey: key.rawValue)
    }

    /// Returns stored object (optional) if any.
    class func getObjectWithKey<T: Decodable>(_ key: MVDefaultsKey, type: T.Type) -> T? {
        if let savedData = UserDefaults.standard.data(forKey: key.rawValue) {
            let object = try? JSONDecoder().decode(type, from: savedData)
            return object
        }

        return UserDefaults.standard.object(forKey: key.rawValue) as? T
    }
}

And here's the test (spec) that I wrote for testing the Defaults methods. All passed! ✅

MVDefaultsSpec.swift

@testable import Movieee
import Foundation
import Quick
import Nimble

class MVDefaultsSpec: QuickSpec {
    override func spec() {
        describe("Tests for MVDefaults") {

            context("Tests the whole MVDefaults.") {

                it("tests the store and retrieve function for any Codable object") {

                    let data = stubbedResponse("MovieResult")
                    expect(data).notTo(beNil())
                    let newMovieResult = try? JSONDecoder().decode(MovieResult.self, from: data!)

                    MVDefaults.store(newMovieResult, key: .someOtherKey)

                    let retrievedObject = MVDefaults.getObjectWithKey(.someOtherKey, type: MovieResult.self)

                    // Assert
                    expect(retrievedObject).notTo(beNil())

                    // Assert
                    expect(retrievedObject?.movies?.first?.id).to(equal(newMovieResult?.movies?.first?.id))
                }

                it("tests the store and retrieve function for String") {

                    let string = "Ich bin ein Berliner"

                    MVDefaults.store(string, key: .someOtherKey)

                    let retrievedObject = MVDefaults.getObjectWithKey(.someOtherKey, type: String.self)

                    // Assert
                    expect(retrievedObject).notTo(beNil())

                    // Assert
                    expect(retrievedObject).to(equal(string))
                }

                it("tests the removal function") {

                    MVDefaults.removeDefaultsWithKey(.someOtherKey)

                    let anyRetrievedObject = UserDefaults.standard.object(forKey: MVDefaultsKey.someOtherKey.rawValue)
                    let stringRetrievedObject = MVDefaults.getObjectWithKey(.someOtherKey, type: String.self)

                    // Assert
                    expect(anyRetrievedObject).to(beNil())

                    // Assert
                    expect(stringRetrievedObject).to(beNil())
                }

                it("tests the store and retrieve function for Bool") {

                    let someBool: Bool = true

                    MVDefaults.store(someBool, key: .someOtherKey)

                    let retrievedObject = MVDefaults.getObjectWithKey(.someOtherKey, type: Bool.self)

                    // Assert
                    expect(retrievedObject).to(equal(someBool))

                    // Assert
                    expect(retrievedObject).notTo(beNil())
                }
            }
        }
    }
}