Ouch! Fix terrible db listener leak (#828)

Author: SUPERCILEX

database/src/main/java/com/firebase/ui/database/CachingObservableSnapshotArray.java

@@ -43,6 +43,14 @@ public T getObject(int index) {
         }
     }
 
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        clearData();
+    }
+
+    /** @deprecated use {@link ObservableSnapshotArray#onDestroy()} instead */
+    @Deprecated
     protected void clearData() {
         getSnapshots().clear();
         mObjectCache.clear();

database/src/main/java/com/firebase/ui/database/FirebaseArray.java

@@ -14,8 +14,6 @@
 
 package com.firebase.ui.database;
 
-import android.support.annotation.NonNull;
-
 import com.google.firebase.database.ChildEventListener;
 import com.google.firebase.database.DataSnapshot;
 import com.google.firebase.database.DatabaseError;
@@ -66,30 +64,17 @@ protected List<DataSnapshot> getSnapshots() {
     }
 
     @Override
-    public ChangeEventListener addChangeEventListener(@NonNull ChangeEventListener listener) {
-        boolean wasListening = isListening();
-        super.addChangeEventListener(listener);
-
-        // Only start listening when the first listener is added
-        if (!wasListening) {
-            mQuery.addChildEventListener(this);
-            mQuery.addValueEventListener(this);
-        }
-
-        return listener;
+    protected void onCreate() {
+        super.onCreate();
+        mQuery.addChildEventListener(this);
+        mQuery.addValueEventListener(this);
     }
 
     @Override
-    public void removeChangeEventListener(@NonNull ChangeEventListener listener) {
-        super.removeChangeEventListener(listener);
-
-        // Clear data when all listeners are removed
-        if (!isListening()) {
-            mQuery.removeEventListener((ValueEventListener) this);
-            mQuery.removeEventListener((ChildEventListener) this);
-
-            clearData();
-        }
+    protected void onDestroy() {
+        super.onDestroy();
+        mQuery.removeEventListener((ValueEventListener) this);
+        mQuery.removeEventListener((ChildEventListener) this);
     }
 
     @Override

database/src/main/java/com/firebase/ui/database/FirebaseIndexArray.java

@@ -14,7 +14,6 @@
 
 package com.firebase.ui.database;
 
-import android.support.annotation.NonNull;
 import android.support.v7.widget.RecyclerView;
 import android.util.Log;
 
@@ -85,10 +84,25 @@ public String parseSnapshot(DataSnapshot snapshot) {
                 return snapshot.getKey();
             }
         });
+    }
 
+    @Override
+    protected void onCreate() {
+        super.onCreate();
         mKeySnapshots.addChangeEventListener(this);
     }
 
+    @Override
+    protected void onDestroy() {
+        super.onDestroy();
+        mKeySnapshots.removeChangeEventListener(this);
+
+        for (DatabaseReference ref : mRefs.keySet()) {
+            ref.removeEventListener(mRefs.get(ref));
+        }
+        mRefs.clear();
+    }
+
     @Override
     public void onChildChanged(EventType type, DataSnapshot snapshot, int index, int oldIndex) {
         switch (type) {
@@ -121,29 +135,11 @@ public void onCancelled(DatabaseError error) {
         Log.e(TAG, "A fatal error occurred retrieving the necessary keys to populate your adapter.");
     }
 
-    @Override
-    public void removeChangeEventListener(@NonNull ChangeEventListener listener) {
-        super.removeChangeEventListener(listener);
-        if (!isListening()) {
-            for (DatabaseReference ref : mRefs.keySet()) {
-                ref.removeEventListener(mRefs.get(ref));
-            }
-
-            clearData();
-        }
-    }
-
     @Override
     protected List<DataSnapshot> getSnapshots() {
         return mDataSnapshots;
     }
 
-    @Override
-    protected void clearData() {
-        super.clearData();
-        mRefs.clear();
-    }
-
     private int getIndexForKey(String key) {
         int dataCount = size();
         int index = 0;

database/src/main/java/com/firebase/ui/database/ObservableSnapshotArray.java

@@ -51,6 +51,8 @@ public ObservableSnapshotArray(@NonNull SnapshotParser<E> parser) {
     public ChangeEventListener addChangeEventListener(@NonNull ChangeEventListener listener) {
         Preconditions.checkNotNull(listener);
 
+        boolean wasListening = isListening();
+
         mListeners.add(listener);
         for (int i = 0; i < size(); i++) {
             listener.onChildChanged(ChangeEventListener.EventType.ADDED, get(i), i, -1);
@@ -59,20 +61,37 @@ public ChangeEventListener addChangeEventListener(@NonNull ChangeEventListener l
             listener.onDataChanged();
         }
 
+        if (!wasListening) { onCreate(); }
+
         return listener;
     }
 
+    /**
+     * Called when the {@link ObservableSnapshotArray} is active and should start listening to the
+     * Firebase database.
+     */
+    @CallSuper
+    protected void onCreate() {}
+
     /**
      * Detach a {@link com.google.firebase.database.ChildEventListener} from this array.
      */
     @CallSuper
     public void removeChangeEventListener(@NonNull ChangeEventListener listener) {
         mListeners.remove(listener);
 
-        // Reset mHasDataChanged if there are no more listeners
-        if (!isListening()) {
-            mHasDataChanged = false;
-        }
+        if (!isListening()) { onDestroy(); }
+    }
+
+    /**
+     * Called when the {@link ObservableSnapshotArray} is inactive and should stop listening to the
+     * Firebase database.
+     * <p>
+     * All data should also be cleared here.
+     */
+    @CallSuper
+    protected void onDestroy() {
+        mHasDataChanged = false;
     }
 
     /**