Saving an Array of Nsurl to Nsuserdefaults

Saving an array of NSURL to NSUserDefaults

when saving, save the absolute strings of the urls. when loading use NSURL(URLString:) to make the strings into urls again

import UIKit

class ViewController: UIViewController {
    var urlsArray : [NSURL]?

    func load () {
        var urls : [NSURL] = []

        let stringsArray = NSUserDefaults.standardUserDefaults().objectForKey("stringsArray") as [String]?

        if let array = stringsArray {
            for string in array {
                var url = NSURL(string: string)
                urls.append(url!) //no null check
            }
        }

        self.urlsArray = urls
    }

    func save () {
        var strings : [String] = []

        if let array = self.urlsArray {
            for url in array {
                var string = url.absoluteString
                strings.append(string!) ////no null check
            }
        }

        NSUserDefaults.standardUserDefaults().setObject(strings, forKey: "stringsArray")
    }

}

saving can be reduced with KVC.

    func save () {
        var strings : [String] = []

        if let array = self.urlsArray as NSArray? {
            strings = array.valueForKeyPath("absoluteStrings")
        }

        NSUserDefaults.standardUserDefaults().setObject(strings, forKey: "stringsArray")
    }

Converting [NSURL] into [String] for NSUserDefaults?

Using NSData

You can convert each NSURL to NSData in order to save it

func save(urls: [NSURL]) {
    let urlsData = urls.map { $0.dataRepresentation }
    NSUserDefaults.standardUserDefaults().setObject(urlsData, forKey: "urlsData")
}

Later on you can retrieve the NSData array and convert it back to [NSURL]

func load() -> [NSURL]? {
    let retrievedData = NSUserDefaults.standardUserDefaults().arrayForKey("urlsData") as? [NSData]
    return retrievedData?.map { NSURL(dataRepresentation: $0, relativeToURL: nil) }
}

Using String

Alternatively you can save the urls as String(s)

func save(urls: [NSURL]) {
    let urlsData = urls.map { $0.absoluteString }
    NSUserDefaults.standardUserDefaults().setObject(urlsData, forKey: "urlsData")
}

func load() -> [NSURL?]? {
    let retrievedData = NSUserDefaults.standardUserDefaults().arrayForKey("urlsData") as? [String]
    return retrievedData?.map { NSURL(string: $0) }
}

As discussed in the comments below, if data is written to NSUserDefaults exclusively with the save function, we know that every element of the array is a String representing a valid NSURL.

So we can change the return type of load from [NSURL?]? to [NSURL]? using this alternate version of load.

func load() -> [NSURL]? {
    let retrievedData = NSUserDefaults.standardUserDefaults().arrayForKey("urlsData") as? [String]
    return retrievedData?.flatMap { NSURL(string: $0) }
}

Saving an array to NSUserDefaults

You can't directly store an NSURL in NSUserDefaults, only NSData, NSString, NSNumber, NSDate, NSArray, or NSDictionary; also, any NSArray or NSDictionary may only contain objects of these types. You'll have to convert the NSURLs into one of these types, most likely by using absoluteString to convert them into NSStrings.

How Do I Save an Array of Objects to NSUserDefaults?

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))]

How to save an array of objects to NSUserDefault with swift?

From the Property List Programming Guide:

If a property-list object is a container (that is, an array or dictionary), all objects contained within it must also be property-list objects. If an array or dictionary contains objects that are not property-list objects, then you cannot save and restore the hierarchy of data using the various property-list methods and functions.

You'll need to convert the object to and from an NSData instance using NSKeyedArchiver and NSKeyedUnarchiver.

For example:

func savePlaces(){
    let placesArray = [Place(lat: 123, lng: 123, name: "hi")]
    let placesData = NSKeyedArchiver.archivedDataWithRootObject(placesArray)
    NSUserDefaults.standardUserDefaults().setObject(placesData, forKey: "places")
}

func loadPlaces(){
    let placesData = NSUserDefaults.standardUserDefaults().objectForKey("places") as? NSData

    if let placesData = placesData {
        let placesArray = NSKeyedUnarchiver.unarchiveObjectWithData(placesData) as? [Place]

        if let placesArray = placesArray {
            // do something…
        }

    }
}

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