How Do I Save an Array of Objects to NSUserDefaults?

Question

I was wondering how to save an array of objects to a NSUserDefault. I've read about encoding the data array, but was unsure about how the process works.

This is my array:

//EventData class with EventDataArray
class EventData {
    
    static var EventDataArray: [EventModel] = []
    
}

And this is my data model:

struct EventModel {
    var id = UUID()
    var eventName: String
    var fromTime: Date
    var toTime: Date
    var fromTimeString: String
    var toTimeString: String
    var color: UIColor
}

EDIT: UPDATED ARRAY CLASS

class EventData: Codable {
    
    static var EventDataArray: [EventModel] = []
    
}

I would appreciate any advice on the topic!

Leo Dabus · Accepted Answer · 2021-01-27T13:47:18.190

To save a structure in UserDefaults you need to first encode it to be able to save it as Data. So you need to make your custom structure conform to Codable:

struct Event: Codable {
    let id: UUID
    let name: String
    let start, end: Date
    let fromTime, toTime: String
    let color: Color
    init(id: UUID = .init(),
         name: String,
         start: Date,
         end: Date,
         fromTime: String,
         toTime: String,
         color: Color) {
        self.id = id
        self.name = name
        self.start = start
        self.end = end
        self.fromTime = fromTime
        self.toTime = toTime
        self.color = color
    }
}

Note that you can not conform UIColor to Codable but you can create a custom Color structure:

struct Color: Codable {
    let (r, g, b, a): (CGFloat, CGFloat, CGFloat, CGFloat)
}

extension Color {
    init?(_ uiColor: UIColor) {
        var (r, g, b, a): (CGFloat,CGFloat,CGFloat,CGFloat) = (0, 0, 0, 0)
        guard uiColor.getRed(&r, green: &g, blue: &b, alpha: &a) else { return nil }
        self.init(r: r, g: g, b: b, a: a)
    }
    var color: UIColor { .init(red: r, green: g, blue: b, alpha: a) }
}

extension UIColor {
    convenience init(_ color: Color) {
        self.init(red: color.r, green: color.g, blue: color.b, alpha: color.a)
    }
    var color: Color? { Color(self) }
}

Regarding your class you can also make it conform to Codable or inherit from NSObject and conform to NSCoding:

class Events: NSObject, NSCoding {
    private override init() { }
    static var shared = Events()
    var events: [Event] = []
    required init(coder decoder: NSCoder) {
        events = try! JSONDecoder().decode([Event].self, from: decoder.decodeData()!)
    }
    func encode(with coder: NSCoder) {
        try! coder.encode(JSONEncoder().encode(events))
    }
}

Playground testing:

Events.shared.events = [.init(name: "a",
                              start: Date(),
                              end: Date(),
                              fromTime: "fromTime",
                              toTime: "toTime",
                              color: .init(r: 0, g: 0, b: 1, a: 1)),
                        .init(name: "b",
                              start: Date(),
                              end: Date(),
                              fromTime: "fromTimeB",
                              toTime: "toTimeB",
                              color: .init(r: 0, g: 1, b: 0, a: 1))]

print(Events.shared.events)
let data = try! NSKeyedArchiver.archivedData(withRootObject: Events.shared, requiringSecureCoding: false)
UserDefaults.standard.set(data, forKey: "events")
Events.shared.events = []
print(Events.shared.events)
let loadedData = UserDefaults.standard.data(forKey: "events")!
Events.shared = try! NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(loadedData) as! Events
print(Events.shared.events)

This will print

[Event(id: C7D9475B-773E-4272-84CC-56CAEAA73D0C, name: "a", start: 2021-01-26 05:17:30 +0000, end: 2021-01-26 05:17:30 +0000, fromTime: "fromTime", toTime: "toTime", color: Color(r: 0.0, g: 0.0, b: 1.0, a: 1.0)), Event(id: 0BEA4225-2F63-4EEB-AF10-F3EF4C84D050, name: "b", start: 2021-01-26 05:17:30 +0000, end: 2021-01-26 05:17:30 +0000, fromTime: "fromTimeB", toTime: "toTimeB", color: Color(r: 0.0, g: 1.0, b: 0.0, a: 1.0))]
[]
[Event(id: C7D9475B-773E-4272-84CC-56CAEAA73D0C, name: "a", start: 2021-01-26 05:17:30 +0000, end: 2021-01-26 05:17:30 +0000, fromTime: "fromTime", toTime: "toTime", color: Color(r: 0.0, g: 0.0, b: 1.0, a: 1.0)), Event(id: 0BEA4225-2F63-4EEB-AF10-F3EF4C84D050, name: "b", start: 2021-01-26 05:17:30 +0000, end: 2021-01-26 05:17:30 +0000, fromTime: "fromTimeB", toTime: "toTimeB", color: Color(r: 0.0, g: 1.0, b: 0.0, a: 1.0))]

Ok, but how do I make the array inside EventData conform to Codable? Is this possible now that the structures EventModel and Color are now supported by Codable? — Aneesh Poddutur, Jan 27 '21 at 08:35
The array already conforms to Codable. If Event conforms to Codable the array conforms as well as you can see I am encoding and decoding `[Event].self` — Leo Dabus, Jan 27 '21 at 13:12
Ok, I made the class object conform to codable, would the save and read methods be the same? This is a different question I made with a bit more context: https://stackoverflow.com/questions/65916487/trouble-saving-and-reading-static-object-array-to-nsdefaults — Aneesh Poddutur, Jan 27 '21 at 13:44
Yes, with a bit of tweaking your solution worked. Thank you for the help! — Aneesh Poddutur, Jan 27 '21 at 13:57

The Swift Coder · Answer 2 · 2021-01-26T06:37:39.870

0

Simply use: UserDefaults().set(try? PropertyListEncoder().encode(EventDataArray), forKey: "eventDataPersisted") (of course, feel free to name the key whatever you want).

Also, as a rule of thumb, variable names typically follow camelCase.

edited Jan 26 '21 at 06:37

answered Jan 26 '21 at 05:04

The Swift Coder

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How Do I Save an Array of Objects to NSUserDefaults?

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