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I'm working on an iOS app that uses a Realm database. In my AppDelegate, I define a Realm result set like this:

var results: Results<RealmWidget>!
var notificationToken: NotificationToken? = nil

do 
 let realm = try Realm()
 if results == nil 
 results = realm.objects(RealmWidget.self)
 
 catch 
 print(error.localizedDescription)

I observe this result set for changes like this:

if notificationToken == nil 
 notificationToken = results.observe (changes: RealmCollectionChange) in
 switch changes 
 case .update(_, _, let insertions, _):
 if insertions.count > 0 
 // show badge on tab bar
 // play sound to get the user's attention
 
 default:
 break
 
 

Anytime a new RealmWidget object is inserted in the database (which happens as a result of receiving data from a server), I want to show a badge on the UITabBar in my UI. This code appears to be working properly.

In another part of my app, I have a view controller with a UITableView that is used to display all of the RealmWidget objects (sorted by a timestamp). Inside of that view controller, I also have a result set that I observe for changes so I know when to reload the tableview. That code looks like this:

var results: Results<RealmWidget>!
var notificationToken: NotificationToken? = nil

class MyViewController: UIViewController, UITableViewDelegate, UITableViewDataSource 

 override func viewDidLoad() 
 super.viewDidLoad()

 results = RealmHelper.getRealmWidgets() // helper method that queries Realm for all of the Widget objects and sorts them by timestamp
 notificationToken = results.observe [weak self] (changes: RealmCollectionChange) in
 DispatchQueue.main.async 
 self!.tableView.reloadData()
 
 
 

This code also appeared to be working properly until I added code to play a sound into the observation block in my AppDelegate. Then I realized that anytime I delete a row from the UITableView in this view controller, I was also hearing the sound play. This was unexpected because I should only be adding the badge to the UITabBar and playing the sound when there is an insertion, not a deletion.

I added some debug code into the observation block that's defined in my AppDelegate so it looks like this:

if notificationToken == nil 
 notificationToken = results.observe (changes: RealmCollectionChange) in
 switch changes 
 case .update(_, let deletions, let insertions, let modifications):
 print("widget deletion count: (deletions.count)")
 print("widget insertion count: (insertions.count)")
 print("widget modification count: (modifications.count)")
 if insertions.count > 0 
 // show badge on tab bar
 // play sound to get the user's attention
 
 default:
 break
 
 

When I run the app, switch to the view controller with the tableview and then delete one of the rows (which causes the corresponding RealmWidget object to be deleted from the database), I see the following output printed in the debug console:

widget deletion count: 2
widget insertion count: 1
widget modification count: 0

A couple of things about this are unclear to me:

• why is the deletion count 2 when I only deleted one RealmWidget object?


• why is the insertion count 1 when I didn't add/insert any RealmWidget objects?

If anyone can explain what's happening here I would certainly appreciate the help!

-- EDIT --

I added the same debug code into my observation block that is defined inside the view controller and noticed something else strange. When this "problem" occurs, I see this output in the debug console:

widget deletion count (AppDelegate): 2
widget insertion count (AppDelegate): 1
widget modification count (AppDelegate): 0

widget deletion count (View controller): 1
widget insertion count (View controller): 0
widget modification count (View controller): 0

So the observation block in my view controller shows 1 deletion but the observation block in my AppDelegate shows 2 deletions and 1 insertion! Oddly enough, this doesn't happen 100% of the time. If my UITableView is showing 10 RealmWidget objects and I delete them one at a time, about 75% of the time, I see the above output in the console. But the other 25% of the time, the output is exactly what I was expecting to see:

widget deletion count (AppDelegate): 1
widget insertion count (AppDelegate): 0
widget modification count (AppDelegate): 0

widget deletion count (View controller): 1
widget insertion count (View controller): 0
widget modification count (View controller): 0

1 deletion in both observation blocks. I'm even more confused now than I was before! ;-)