conform to FIRCollection

Author: morganchen12

FirebaseDatabaseUI/FUIArray.m

@@ -47,7 +47,6 @@ - (instancetype)initWithQuery:(FIRDatabaseQuery *)query delegate:(id<FUICollecti
     self.query = query;
     self.handles = [NSMutableSet setWithCapacity:4];
     self.delegate = delegate;
-    [self initListeners];
   }
   return self;
 }
@@ -63,14 +62,13 @@ + (instancetype)arrayWithQuery:(id<FUIDataObservable>)query {
 #pragma mark - Memory management methods
 
 - (void)dealloc {
-  for (NSNumber *handle in _handles) {
-    [_query removeObserverWithHandle:handle.unsignedIntegerValue];
-  }
+  [self invalidate];
 }
 
 #pragma mark - Private API methods
 
-- (void)initListeners {
+- (void)observeQuery {
+  if (self.handles.count == 4) { /* don't duplicate observers */ return; }
   FIRDatabaseHandle handle;
   handle = [self.query observeEventType:FIRDataEventTypeChildAdded
       andPreviousSiblingKeyWithBlock:^(FIRDataSnapshot *snapshot, NSString *previousChildKey) {
@@ -153,6 +151,12 @@ - (void)initListeners {
   [_handles addObject:@(handle)];
 }
 
+- (void)invalidate {
+  for (NSNumber *handle in _handles) {
+    [_query removeObserverWithHandle:handle.unsignedIntegerValue];
+  }
+}
+
 - (NSUInteger)indexForKey:(NSString *)key {
   NSParameterAssert(key != nil);
 

FirebaseDatabaseUI/FUICollection.h

@@ -38,6 +38,9 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (FIRDataSnapshot *)snapshotAtIndex:(NSInteger)index;
 
+- (void)observeQuery;
+- (void)invalidate;
+
 @end
 
 /**

FirebaseDatabaseUI/FUIDataSource.m

@@ -40,6 +40,7 @@ - (instancetype)initWithArray:(FUIArray *)array {
   if (self) {
     _array = array;
     _array.delegate = self;
+    [array observeQuery];
   }
   return self;
 }

FirebaseDatabaseUI/FUISortedArray.m

@@ -63,6 +63,7 @@ - (void)dealloc {
 }
 
 - (void)observeQuery {
+  if (self.handles.count == 4) { /* don't duplicate observers */ return; }
   FIRDatabaseHandle handle;
   handle = [self.query observeEventType:FIRDataEventTypeChildAdded
          andPreviousSiblingKeyWithBlock:^(FIRDataSnapshot *snapshot, NSString *previousChildKey) {