UICollectionView insertItemsAtIndexPaths: raising error - ios

Question

I know there are all sorts of questions related to this, but none of the answers answered this.
Anyways, I have a UICollectionView that should be scroll forever, but I can't seem to get insertItemsAtIndexPaths: to work. It raises the error:
*** Assertion failure in -[UICollectionView _endItemAnimations], /SourceCache/UIKit/UIKit-2935.137/UICollectionView.m:3688
Here is my code:
#import "ImageSliderViewController.h"
#define ITEM_CELL_IDENTIFIER #"ItemCell"
#interface ImageSliderViewController ()
#end
#implementation ImageSliderViewController
- (void)viewDidLoad
{
[super viewDidLoad];
[self setupCollectionView];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
}
#pragma mark - UICollectionView methods
-(void)setupCollectionView {
self.items = [[NSMutableArray alloc] init];
loadingGap = 5;
self.collectionView.delegate = self;
self.collectionView.dataSource = self;
[self.collectionView registerClass:[ImageSliderCell class] forCellWithReuseIdentifier:ITEM_CELL_IDENTIFIER];
UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
[flowLayout setScrollDirection:UICollectionViewScrollDirectionHorizontal];
[flowLayout setMinimumInteritemSpacing:0.0f];
[flowLayout setMinimumLineSpacing:0.0f];
[self.collectionView setPagingEnabled:YES];
[self.collectionView setCollectionViewLayout:flowLayout];
[self loadMorePosts];
}
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
return 1;
}
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return self.items.count;
}
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
ImageSliderCell *cell = (ImageSliderCell *)[collectionView dequeueReusableCellWithReuseIdentifier:ITEM_CELL_IDENTIFIER forIndexPath:indexPath];
cell.imageTitle.text = [NSString stringWithFormat:#"%ld",(long)indexPath.item];
NSLog(#"%d : %d",indexPath.item,self.items.count-1);
if (indexPath.item >= self.items.count-1) {
[self loadMorePosts];
}
return cell;
}
-(CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
CGSize size = self.collectionView.frame.size;
size.height = size.height/2;
return size;
}
- (void)loadMorePosts
{
NSLog(#"Loading new items");
NSUInteger loopTill = self.items.count + loadingGap;
NSMutableArray *indexPathsToLoad = [NSMutableArray new];
while (self.items.count < loopTill) {
[indexPathsToLoad addObject:[NSIndexPath indexPathForItem:self.items.count inSection:0]];
NSLog(#"Added section %d",self.items.count);
AsyncImageView *img = [[DatabaseFetcher alloc] getPostWithID:[NSString stringWithFormat:#"%lu",(unsigned long)self.items.count]
inSection:#"features"
withFrame:CGRectMake(0, 0, self.collectionView.frame.size.width, self.collectionView.frame.size.height)];
[self.items addObject:#[img]];
};
[self.collectionView reloadItemsAtIndexPaths:indexPathsToLoad];
}
#end
Thanks in advance!
Update: I updated the code to use reloadItemsAtIndexPaths and some other improvements base on suggestions. Thanks!

Answer 1

[NSIndexPath indexPathForItem:self.items.count inSection:0]
Should be:
[NSIndexPath indexPathForItem:self.items.count - 1 inSection:0]
update
And you should submit all of your insertions at once by building up an NSMutableArray of index paths in your loop and inserting them at the end (as you've done and commented out). Alternatively, you can put your loop inset of a performBatchUpdates block.

Answer 2

thanks for all the answers.
It looks like I had a miscalculation when trying one of the solutions on the other thread. Here's my new solution that works:
-(void)addNewItems
{
NSLog(#"Loading new items");
NSMutableArray *indexPathsToLoad = [NSMutableArray new];
for (int i = 0; i < LOADING_GAP; i++) {
[indexPathsToLoad addObject:[NSIndexPath indexPathForItem:self.items.count inSection:0]];
[self.items addObject:#"Test"];
}
if (self.items.count == LOADING_GAP) {
[self.collectionView reloadData];
} else {
[self.collectionView insertItemsAtIndexPaths:indexPathsToLoad];
}
}
Thank you!