Realm Java and Asynchronous Threading: Frozen Object State Synchronization

Answer

To keep frozen objects in sync after a background writeAsync transaction, attach a RealmChangeListener to the Realm instance (or to the specific RealmResults/RealmObject) on the UI thread. The listener fires on that thread’s Looper once the transaction is committed, allowing you to obtain a fresh frozen snapshot.

Steps to refresh frozen objects

1. On the UI thread, open the Realm instance and add a listener:

2. realm.addChangeListener { realm, _ ->
       // Obtain a new frozen snapshot for the object you are observing
       val freshFrozen = realm.where(MyModel::class.java)
                              .equalTo("id", currentId)
                              .findFirst()
                              ?.freeze()
       // Update UI with freshFrozen
     }

3. Perform the background update with writeAsync:

4. backgroundRealm.writeAsync { transaction ->
       val obj = transaction.where(MyModel::class.java)
                            .equalTo("id", targetId)
                            .findFirst()
       obj?.field = newValue
     }

5. The listener callback runs on the UI thread after the commit, giving you an up‑to‑date frozen object without manual polling.

Efficiently obtaining a live object for an update

If you already have a frozen object and need to modify it:

• Extract its primary key value (id).
• Query the Realm on any thread using the indexed primary key:

• val live = realm.where(MyModel::class.java)
                  .equalTo("id", frozenObject.id)
                  .findFirst()

• Because the primary key is indexed (annotated with @PrimaryKey), this lookup is O(log n) and avoids a full table scan.
• If you already hold a live reference (e.g., from a RealmResults list), you can skip the lookup and modify the managed object directly inside a transaction.

Missing diagnostic detail: Confirm that the UI thread where you add the listener is attached to a Looper (e.g., the main thread or a HandlerThread). If it lacks a Looper, the change listener will not be delivered and you must post to a Looper‑bound thread or use Handler(Looper.getMainLooper()).