fix data source init having side effects

Author: morganchen12

FirebaseDatabaseUI/FUICollection.h

@@ -20,7 +20,7 @@
 
 @import Foundation;
 
-@class FUIArray;
+@class FIRDatabaseReference, FIRDatabaseQuery, FIRDataSnapshot;
 @protocol FUICollectionDelegate;
 
 NS_ASSUME_NONNULL_BEGIN

FirebaseDatabaseUI/FUICollectionViewDataSource.h

@@ -20,19 +20,17 @@
 
 @import UIKit;
 
-#import "FUIDataSource.h"
+#import <FirebaseDatabaseUI/FUICollection.h>
 
 NS_ASSUME_NONNULL_BEGIN
 
-@class FIRDatabaseReference;
-
 /**
  * FUICollectionViewDataSource provides a class that conforms to the
  * UICollectionViewDataSource protocol which allows UICollectionViews to
  * adopt FUICollectionViewDataSource in order to provide a UICollectionView
  * synchronized to a Firebase reference or query.
  */
-@interface FUICollectionViewDataSource : FUIDataSource<UICollectionViewDataSource>
+@interface FUICollectionViewDataSource : NSObject <UICollectionViewDataSource>
 
 /**
  * The UICollectionView instance that operations (inserts, removals, moves,
@@ -46,16 +44,19 @@ NS_ASSUME_NONNULL_BEGIN
  * The callback to populate a subclass of UICollectionViewCell with an object
  * provided by the datasource.
  */
-@property(strong, nonatomic, readonly) UICollectionViewCell *(^populateCellAtIndexPath)
+@property (strong, nonatomic, readonly) UICollectionViewCell *(^populateCellAtIndexPath)
   (UICollectionView *collectionView, NSIndexPath *indexPath, FIRDataSnapshot *object);
 
+/**
+ * The number of items in the data source.
+ */
+@property (nonatomic, readonly) NSUInteger count;
+
 /**
  * Initialize an instance of FUICollectionViewDataSource that populates
  * UICollectionViewCells with FIRDataSnapshots.
  * @param collection A FUICollection that the data source uses to pull snapshots
  *   from Firebase Database.
- * @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
  *   source, so if you capture self in the closure and also claim ownership of the
@@ -64,7 +65,6 @@ NS_ASSUME_NONNULL_BEGIN
  *   UICollectionViewCells with FIRDataSnapshots.
  */
 - (instancetype)initWithCollection:(id<FUICollection>)collection
-                              view:(UICollectionView *)view
                       populateCell:(UICollectionViewCell *(^)(UICollectionView *collectionView,
                                                               NSIndexPath *indexPath,
                                                               FIRDataSnapshot *object))populateCell NS_DESIGNATED_INITIALIZER;
@@ -73,8 +73,6 @@ NS_ASSUME_NONNULL_BEGIN
  * Initialize an unsorted instance of FUICollectionViewDataSource that populates
  * UICollectionViewCells with FIRDataSnapshots.
  * @param query A Firebase query to bind the data source to.
- * @param collectionView 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
  *   source, so if you capture self in the closure and also claim ownership of the
@@ -83,12 +81,23 @@ NS_ASSUME_NONNULL_BEGIN
  *   UICollectionViewCells with FIRDataSnapshots.
  */
 - (instancetype)initWithQuery:(FIRDatabaseQuery *)query
-                         view:(UICollectionView *)collectionView
                  populateCell:(UICollectionViewCell *(^)(UICollectionView *collectionView,
                                                          NSIndexPath *indexPath,
                                                          FIRDataSnapshot *object))populateCell;
 
-- (instancetype)initWithCollection:(id<FUICollection>)collection NS_UNAVAILABLE;
+- (instancetype)init NS_UNAVAILABLE;
+
+/**
+ * Attaches the data source to a collection view and begins sending updates immediately.
+ * @param view An instance of UICollectionView that the data source should push
+ *   updates to.
+ */
+- (void)bindToView:(UICollectionView *)view;
+
+/**
+ * Detaches the data source from a view and stops sending any updates.
+ */
+- (void)unbind;
 
 @end
 

FirebaseDatabaseUI/FUICollectionViewDataSource.m

@@ -19,33 +19,54 @@
 // clang-format on
 
 #import "FUICollectionViewDataSource.h"
+#import "FUIArray.h"
 
 @import FirebaseDatabase;
 
+@interface FUICollectionViewDataSource ()
+
+@property (nonatomic, readonly, nonnull) id<FUICollection> collection;
+
+@end
+
 @implementation FUICollectionViewDataSource
 
 #pragma mark - FUIDataSource initializer methods
 
 - (instancetype)initWithCollection:(id<FUICollection>)collection
-                              view:(UICollectionView *)view
                       populateCell:(UICollectionViewCell * (^)(UICollectionView *,
                                                                NSIndexPath *,
                                                                FIRDataSnapshot *))populateCell {
-  self = [super initWithCollection:collection];
+  self = [super init];
   if (self) {
-    _collectionView = view;
+    _collection = collection;
     _populateCellAtIndexPath = populateCell;
   }
   return self;
 }
 
 - (instancetype)initWithQuery:(FIRDatabaseQuery *)query
-                         view:(UICollectionView *)collectionView
                  populateCell:(UICollectionViewCell *(^)(UICollectionView *,
                                                          NSIndexPath *,
                                                          FIRDataSnapshot *))populateCell {
   FUIArray *array = [[FUIArray alloc] initWithQuery:query];
-  return [self initWithCollection:array view:collectionView populateCell:populateCell];
+  return [self initWithCollection:array populateCell:populateCell];
+}
+
+- (NSUInteger)count {
+  return self.collection.count;
+}
+
+- (void)bindToView:(UICollectionView *)view {
+  self.collectionView = view;
+  view.dataSource = self;
+  [self.collection observeQuery];
+}
+
+- (void)unbind {
+  self.collectionView.dataSource = nil;
+  self.collectionView = nil;
+  [self.collection invalidate];
 }
 
 #pragma mark - FUICollectionDelegate methods
@@ -75,7 +96,7 @@ - (void)array:(FUIArray *)array didMoveObject:(id)object
 
 - (nonnull UICollectionViewCell *)collectionView:(nonnull UICollectionView *)collectionView
                           cellForItemAtIndexPath:(nonnull NSIndexPath *)indexPath {
-  FIRDataSnapshot *snap = [self.items objectAtIndex:indexPath.row];
+  FIRDataSnapshot *snap = [self.collection.items objectAtIndex:indexPath.item];
 
   UICollectionViewCell *cell = self.populateCellAtIndexPath(collectionView, indexPath, snap);
 
@@ -88,7 +109,7 @@ - (NSInteger)numberOfSectionsInCollectionView:(nonnull UICollectionView *)collec
 
 - (NSInteger)collectionView:(nonnull UICollectionView *)collectionView
      numberOfItemsInSection:(NSInteger)section {
-  return self.count;
+  return self.collection.count;
 }
 
 @end
@@ -100,8 +121,8 @@ - (FUICollectionViewDataSource *)bindToQuery:(FIRDatabaseQuery *)query
                                                                         NSIndexPath *,
                                                                         FIRDataSnapshot *))populateCell {
   FUICollectionViewDataSource *dataSource =
-    [[FUICollectionViewDataSource alloc] initWithQuery:query view:self populateCell:populateCell];
-  self.dataSource = dataSource;
+    [[FUICollectionViewDataSource alloc] initWithQuery:query populateCell:populateCell];
+  [dataSource bindToView:self];
   return dataSource;
 }