Persist data between app launches - ios

Question

I have a class to handle a simple note creator in my app. At the moment, notes are stored using an array of custom Note objects. How can I save the contents of this array when the app closes and load them again when the app is re-opened? I've tried NSUserDefaults, but I can't figure out how to save the array since it isn't just comprised of Strings.
Code:
Note.swift
class Note {
var contents: String
// an automatically generated note title, based on the first line of the note
var title: String {
// split into lines
let lines = contents.componentsSeparatedByCharactersInSet(NSCharacterSet.newlineCharacterSet()) as [String]
// return the first
return lines[0]
}
init(text: String) {
contents = text
}
}
var notes = [
Note(text: "Contents of note"),]

Answer 1

There are different approaches to this.
NSCoding
The easiest would be to adopt NSCoding, let Note inherit from NSObject and use NSKeyedArchiver and NSKeyedUnarchiver to write to/from files in the app's sandbox.
Here is a trivial example for this:
final class Feedback : NSObject, NSCoding {
private static let documentsPath = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0]
let content : String
let entry : EntryId
let positive : Bool
let date : NSDate
init(content: String, entry: EntryId, positive : Bool, date :NSDate = NSDate()) {
self.content = content
self.entry = entry
self.positive = positive
self.date = date
super.init()
}
#objc init?(coder: NSCoder) {
if let c = coder.decodeObjectForKey("content") as? String,
let d = coder.decodeObjectForKey("date") as? NSDate {
let e = coder.decodeInt32ForKey("entry")
let p = coder.decodeBoolForKey("positive")
self.content = c
self.entry = e
self.positive = p
self.date = d
}
else {
content = ""
entry = -1
positive = false
date = NSDate()
}
super.init()
if self.entry == -1 {
return nil
}
}
#objc func encodeWithCoder(aCoder: NSCoder) {
aCoder.encodeBool(self.positive, forKey: "positive")
aCoder.encodeInt32(self.entry, forKey: "entry")
aCoder.encodeObject(content, forKey: "content")
aCoder.encodeObject(date, forKey: "date")
}
static func feedbackForEntry(entry: EntryId) -> Feedback? {
let path = Feedback.documentsPath.stringByAppendingString("/\(entry).feedbackData")
if let success = NSKeyedUnarchiver.unarchiveObjectWithFile(path) as? Feedback {
return success
}
else {
return nil
}
}
func save() {
let path = Feedback.documentsPath.stringByAppendingString("/\(entry).feedbackData")
let s = NSKeyedArchiver.archiveRootObject(self, toFile: path)
if !s {
debugPrint("Warning: did not save a Feedback for \(self.entry): \"\(self.content)\"")
}
}
}
Core Data
The more efficient but more complex solution is using Core Data, Apple's ORM-Framework - which's usage is way beyond the scope of a SO answer.
Further Reading
NSHipster article
Archiving programming guide
Core Data programming guide