GEEKING

iOS/RobloxUI/Source/Components/RBInfiniteCollectionView.m

@@ -0,0 +1,167 @@
+//
+//  RBInfiniteCollectionView.m
+//  RobloxMobile
+//
+//  Created by Ariel Lichtin on 10/14/14.
+//  Copyright (c) 2014 ROBLOX. All rights reserved.
+//
+
+#import "RBInfiniteCollectionView.h"
+
+#define NUM_ITEMS_PER_REQUEST 40
+#define START_REQUEST_THRESHOLD 10 // The next request will start when there are 10 elements left
+
+@interface RBInfiniteCollectionView () <UICollectionViewDelegate, UICollectionViewDataSource>
+
+@end
+
+@implementation RBInfiniteCollectionView
+{
+    NSUInteger _numItemsInCollectionView;
+    BOOL _requestInProgress;
+    BOOL _listComplete;
+}
+
+- (instancetype)initWithFrame:(CGRect)frame collectionViewLayout:(UICollectionViewLayout *)layout
+{
+    self = [super initWithFrame:frame collectionViewLayout:layout];
+    if(self)
+    {
+        _numItemsInCollectionView = NUM_ITEMS_PER_REQUEST;
+        _listComplete = NO;
+        _requestInProgress = NO;
+        
+        __weak RBInfiniteCollectionView* weakSelf = self;
+        self.delegate = weakSelf;
+        self.dataSource = weakSelf;
+        
+        [self reloadData];
+    }
+    return self;
+}
+
+- (void)scrollViewDidScroll:(UIScrollView *)scrollView
+{
+    // Get the index of the last visible item
+    NSArray* indexes = [self indexPathsForVisibleItems];
+    NSIndexPath* maxIndex = nil;
+    for(NSIndexPath* index in indexes)
+    {
+        if(maxIndex == nil || maxIndex.row < index.row)
+        {
+            maxIndex = index;
+        }
+    }
+    
+    if(_listComplete == NO && maxIndex.row + START_REQUEST_THRESHOLD > _numItemsInCollectionView)
+    {
+        _numItemsInCollectionView += NUM_ITEMS_PER_REQUEST;
+        
+        [self performBatchUpdates:^
+        {
+            NSMutableArray* indexes = [NSMutableArray array];
+            for(NSUInteger i = _numItemsInCollectionView - NUM_ITEMS_PER_REQUEST; i < _numItemsInCollectionView; ++i)
+            {
+                [indexes addObject:[NSIndexPath indexPathForRow:i inSection:0]];
+            }
+            [self insertItemsAtIndexPaths:indexes];
+        }
+        completion:nil];
+        
+        [self loadElementsAsync];
+    }
+}
+
+- (void)loadElementsAsync
+{
+    if(_infiniteDelegate == nil)
+        return;
+    
+    NSUInteger itemCount = [_infiniteDelegate numItemsInInfiniteCollectionView:self];
+    if(!_listComplete && !_requestInProgress && _numItemsInCollectionView > itemCount)
+    {
+        _requestInProgress = YES;
+
+        NSUInteger itemsToRequest = _numItemsInCollectionView - itemCount;
+
+        void(^block)() = ^()
+        {
+            NSUInteger newItemCount = [_infiniteDelegate numItemsInInfiniteCollectionView:self];
+            
+            NSInteger rangeFrom = itemCount;
+            NSInteger rangeTo = newItemCount;
+            
+            // Update visible elements
+            NSArray* visibleCells = [self indexPathsForVisibleItems];
+            NSMutableArray* cellsToUpdate = [NSMutableArray array];
+            for(NSIndexPath* indexPath in visibleCells)
+            {
+                BOOL inRange = indexPath.row >= rangeFrom && indexPath.row < rangeTo;
+                if(inRange)
+                    [cellsToUpdate addObject:indexPath];
+            }
+            [self reloadItemsAtIndexPaths:cellsToUpdate];
+            
+            NSUInteger numItemsRetrieved = newItemCount - itemCount;
+            _listComplete = numItemsRetrieved < itemsToRequest;
+            if(_listComplete)
+            {
+                // If the list is already complete,
+                // remove the remaining placeholder empty cells
+                NSUInteger totalElements = _numItemsInCollectionView;
+                
+                _numItemsInCollectionView = newItemCount;
+                
+                [self performBatchUpdates:^
+                {
+                    NSMutableArray* indexes = [NSMutableArray array];
+                    for(NSUInteger i = newItemCount; i < totalElements; ++i)
+                    {
+                        [indexes addObject:[NSIndexPath indexPathForRow:i inSection:0]];
+                    }
+                    [self deleteItemsAtIndexPaths:indexes];
+                }
+                completion:nil];
+            }
+            
+            _requestInProgress = NO;
+            
+            [self loadElementsAsync];
+        };
+        
+        [_infiniteDelegate asyncRequestItemsForCollectionView:self numItemsToRequest:itemsToRequest completionHandler:block];
+    }
+}
+
+- (NSUInteger)numItems
+{
+    return _numItemsInCollectionView;
+}
+
+- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
+{
+    return 1;
+}
+
+- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
+{
+    return _numItemsInCollectionView;
+}
+
+- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
+{
+    if(_infiniteDelegate)
+        return [_infiniteDelegate infiniteCollectionView:self cellForItemAtIndexPath:indexPath];
+    else
+        return nil;
+}
+
+- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
+{
+    if(_infiniteDelegate)
+    {
+        [_infiniteDelegate infiniteCollectionView:self didSelectItemAtIndexPath:indexPath];
+    }
+}
+
+@end