Data Persistence

Question

When the app is loaded, I want to know whether I have already saved the data to disk. If it is saved, I just load from disk, if not, I save. for example, I want to save an array(person) using NSUserDefaults.standardUserDefaults()

Save Method:

let defaults = NSUserDefaults.standardUserDefaults()

 if let savedPeople = defaults.objectForKey("people") as? NSData 

     people = NSKeyedUnarchiver.unarchiveObjectWithData(savedPeople) as! [Person]

But how can I know if I have saved the data or not in viewDidLoad()? I don't want to save every time I open the app, and it will also overwrite the data I modified before.

How to know it exists or not? can you give me a simple code to demonstrate. I am not so familiar with this part. — Bog, Sep 25 '15 at 23:08
@rmaddy It sounds like he's using `NSUserDefaults` for persistence. — nhgrif, Sep 26 '15 at 00:29

score 0 · Answer 1 · answered Sep 26 '15 at 01:49

This is how you will do it:

override func viewDidLoad() {
    super.viewDidLoad()

    if let savedPeople = NSUserDefaults.standardUserDefaults().objectForKey("people") {
        // Use savedPeople based on your need
    } else {
        NSUserDefaults.standardUserDefaults().setObject(myArray, forKey: "people")
    }
}

Data Persistence

1 Answers1