Why is the title being repeated? - ios

Question

I am getting the current playing song, and capturing the title and artist, and storing it in parse. For some reason, when the song plays, the program adds 4 or so of the same title/artist. I instead just want one. How do I fix this?
my objects as seen in the parse data browser
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(animated);
NSNotificationCenter.defaultCenter().addObserver(self, selector: "getNowPlayingItem", name: MPMusicPlayerControllerNowPlayingItemDidChangeNotification, object: nil)
musicPlayer.beginGeneratingPlaybackNotifications()
}
func getNowPlayingItem() {
NSNotificationCenter.defaultCenter().removeObserver(self)
if let nowPlaying = musicPlayer.nowPlayingItem {
let title = nowPlaying[MPMediaItemPropertyTitle] as? String
let artisttest = nowPlaying[MPMediaItemPropertyTitle]
if let artist = nowPlaying[MPMediaItemPropertyArtist] as? String{
let objectPointer = PFObject(className: "Pointer")
let object = PFObject(className: "MasterSongs")
let query = PFQuery(className: "Pointer")
query.findObjectsInBackgroundWithBlock({
(objects: [AnyObject]?, error: NSError?) -> Void in
var objectIDs = objects as! [PFObject]
for i in 0...objectIDs.count-1{
self.Parsearray.append((objectIDs[i].valueForKey("title") as? String)!)
// print(self.Parsearray)
}
if self.Parsearray.contains(title!){
print("already in db")
}else{
objectPointer["title"] = title
objectPointer["user"] = PFUser.currentUser()
objectPointer["artist"] = artist
objectPointer.saveInBackgroundWithBlock({ (success: Bool, error: NSError?) -> Void in
if(error != nil){
print(error)
}else{
NSNotificationCenter.defaultCenter().addObserver(self, selector: "getNowPlayingItem", name: MPMusicPlayerControllerNowPlayingItemDidChangeNotification, object: nil)
}
})
}
})
}else{
let objectPointer = PFObject(className: "Pointer")
let query = PFQuery(className: "Pointer")
query.findObjectsInBackgroundWithBlock({
(objects: [AnyObject]?, error: NSError?) -> Void in
var objectIDs = objects as! [PFObject]
for i in 0...objectIDs.count-1{
self.Parsearray.append((objectIDs[i].valueForKey("title") as? String)!)
// print(self.Parsearray)
}
if self.Parsearray.contains(title!){
print("already in db")
}else{
objectPointer["title"] = title
objectPointer["user"] = PFUser.currentUser()
objectPointer["artist"] = "No artist found :("
objectPointer.saveInBackgroundWithBlock({ (success: Bool, error: NSError?) -> Void in
if(error != nil){
print(error)
}else{
NSNotificationCenter.defaultCenter().addObserver(self, selector: "getNowPlayingItem", name: MPMusicPlayerControllerNowPlayingItemDidChangeNotification, object: nil)
}
})
}
})
}
}
}

Answer 1

From the evidence, there's a good chance that the function getNowPlayingItem is being called several times rapidly. It launches queries, a handful of which complete before anything is saved. Those query completions (with no saves done yet) launch a handful of saves and you get a handful of objects.
Check this by printing a message at the start of the method and just before saveInBackground paying attention to the timestamps on the console.
If I'm right, the fix is simple: (a) find out why the method is being called so many times and fix that, or (b) add a boolean instance variable to the enclosing class, call it something like busySaving. At the start of the method, bail out if busySaving is true, otherwise set it to true an carry on. Change your saveInBackground() to saveInBackgroundWithBlock() and reset the busySaving flag in the completion block.
EDIT
Now we see why it's being called repeatedly: because the notification is being received repeatedly. One way to fix (idea (a) above) would be to stop observing that notification (NSNotificationCenter removeObserver) at the start of getNowPlayingItem. Then, since you want to get subsequent notifications, re-add yourself as an observer after the save, using saveInBackgroundWithBlock. Notice this is different from saveInBackground see here for reference.
Idea (b) above still applies as well, if you prefer.