ios - Data Persistence -

when app loaded, want know whether have saved data disk. if saved, load disk, if not, save. example, want save 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 know if have saved data or not in viewdidload()? don't want save every time open app, , overwrite data modified before.

this how it:

override func viewdidload() {     super.viewdidload()      if let savedpeople = nsuserdefaults.standarduserdefaults().objectforkey("people") {         // use savedpeople based on need     } else {         nsuserdefaults.standarduserdefaults().setobject(myarray, forkey: "people")     } }