add doc comments

Author: morganchen12

FirebaseDatabaseUI/FUICollection.h

@@ -25,20 +25,37 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
+/**
+ * A protocol representing a collection of objects from Firebase Database.
+ */
 @protocol FUICollection <NSObject>
 
 @property (nonatomic, readonly, copy) NSArray<FIRDataSnapshot *> *items;
 
 @property (weak, nonatomic, nullable) id<FUICollectionDelegate> delegate;
 
 /**
- * The number of objects in the FirebaseArray.
+ * The number of objects in the collection.
  */
 @property (nonatomic, readonly) NSUInteger count;
 
+/**
+ * The @c FIRDataSnapshot at the given index. May raise fatal errors
+ * if the index is out of bounds.
+ * @param index The index of a snapshot.
+ */
 - (FIRDataSnapshot *)snapshotAtIndex:(NSInteger)index;
 
+/**
+ * Calling this makes the array begin observing updates from its query.
+ * Before this call is made the array is inert and doesn't do anything.
+ */
 - (void)observeQuery;
+
+/**
+ * Cancels all active observations. The array may be reused after this
+ * is called by calling @c observeQuery again.
+ */
 - (void)invalidate;
 
 @end

FirebaseDatabaseUI/FUICollectionViewDataSource.h

@@ -53,7 +53,7 @@ NS_ASSUME_NONNULL_BEGIN
  * UICollectionViewCells with FIRDataSnapshots.
  * @param collection A FUICollection that the data source uses to pull snapshots
  *   from Firebase Database.
- * @param collectionView An instance of a UICollectionView to bind to. This view
+ * @param view An instance of a UICollectionView to bind to. This view
  *   is not retained by its data source.
  * @param populateCell A closure used by the data source to create the cells that
  *   are displayed in the collection view. This closure is retained by the data

FirebaseDatabaseUI/FUIDataSource.h

@@ -40,16 +40,19 @@
 @property (nonatomic, readonly, copy) NSArray *items;
 
 /**
- * Pass through of [FirebaseArray count].
+ * The number of items in the receiver's collection.
  */
 @property (nonatomic, readonly) NSUInteger count;
 
+/**
+ * Takes an FUICollection and immediately starts observing it.
+ */
 - (instancetype)initWithCollection:(id<FUICollection>)collection NS_DESIGNATED_INITIALIZER;
 
 - (instancetype)init NS_UNAVAILABLE;
 
 /**
- * Pass through of [FirebaseArray snapshotAtIndex:].
+ * Returns the snapshot at the given index in the receiver's collection.
  */
 - (FIRDataSnapshot *)objectAtIndex:(NSUInteger)index;
 

FirebaseDatabaseUI/FUISortedArray.h

@@ -28,16 +28,18 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (instancetype)init NS_UNAVAILABLE;
 
-- (instancetype)initWithQuery:(id<FUIDataObservable>)query
+/**
+ * Initializes a sorted collection.
+ * @param query The query the receiver uses to pull updates from Firebase Database.
+ * @param delegate The delegate object that should receive events from the array.
+ * @param sortDescriptor The closure used by the array to sort its contents. This
+ *   block must always return consistent results or the array may raise a fatal error.
+ */
+- (instancetype)initWithQuery:(id<FIRDataObservable>)query
                      delegate:(nullable id<FUICollectionDelegate>)delegate
                sortDescriptor:(NSComparisonResult (^)(FIRDataSnapshot *left,
                                                       FIRDataSnapshot *right))sortDescriptor NS_DESIGNATED_INITIALIZER;
 
-- (void)observeQuery;
-- (void)invalidate;
-
-- (FIRDataSnapshot *)snapshotAtIndex:(NSInteger)index;
-
 @end
 
 NS_ASSUME_NONNULL_END