Loading additional cells at the bottom of UICollectionView

Question

I am trying to automatically get and load the next page of cells when the user scrolls to the bottom of theUICollectionView.

I am able to do so by adding a UIButton in UICollectoinView footer. When user scrolls to the footer and touches the button, new cells are added correctly. UIButton in the footer can be touched again for adding more pages.

I tried to automate it so when the user scrolls to the bottom, the proper method for adding new cells is called automatically:

- (UICollectionReuseableView *)collectionView: (UICollectionView *)collectionView viewForSupplementaryElementOfKind: (NSString *)kind atIndexPath: (NSIndexPath *) indexPath
{

    // code for headerView
    // ...

    // code for footerView
    MySupplementalFooter *footerView = nil;
    if ( [kind isEqual:UICollectionElementKindSectionFooter] )
    {
        footerView = [self.collectionView dequeueReuseableSupplemntaryViewOfKind:kind withReuseIdentifier:@"FooterId" forIndexPath:indexPath];
        if (LoadMoreIsEnabled) 
        {
            footerView.loadMoreFooterButton.setHidden:NO];
            [self loadMoreFooterButtonAction]; // calls the method to add cells to the dictionary for cv 
        } else 
        {
             footerView.loadMoreFooterButton setHidden:YES];
        }

        return footerView;
    }
}

The loadMoreFooterButtonAction method is called, but the entire UICollectionView blanks out. Refreshing the UICollectionView does not bring it back.

Answer 1

In IOS8 there is a UICollectionViewDelegate method willDisplayCell.

func collectionView(collectionView: UICollectionView, willDisplayCell cell: UICollectionViewCell, forItemAtIndexPath indexPath: NSIndexPath) {
    if indexPath.item == (data.count-1) {
        loadData()
    }
}

Answer 2

In table view, you should load more data in willDisplayCell() method. With collections, there is no such a counterpart. But, you can do like this. Hope, it helps.

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    // Other code here ...

    if (indexPath.item == [self.photos count] - 1) {
        [self loadPhotos];
    }

    return cell;
}

- (void)loadPhotos {
    [self showLoadingIndicator];
    self.operation = [client HTTPRequestOperationWithRequest:request success:^(AFHTTPRequestOperation *operation, id responseObject) {
        [self hideLoadingIndicator];

        // Get data
        NSArray *photosData = responseObject[@"data"];
        NSInteger numberOfResults = [photosData count];
        NSInteger totalCount = [self.photos count];

        if (numberOfResults > 0) {
            NSMutableArray *indexPaths = [NSMutableArray new];

            for (NSInteger i = 0; i < numberOfResults; i++) {
                Photo *photo = [Photo new];
                photo._id = [photoData[@"id"] integerValue];
                photo.url = photoData[@"url"];

                [self.photos addObject:photo];
                [indexPaths addObject:[NSIndexPath indexPathForRow:totalCount + i
                                                     inSection:0]];
            }

            [self.collectionView performBatchUpdates:^{
                [self.collectionView insertItemsAtIndexPaths:indexPaths];
            } completion:nil];
        }        
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        [self hideLoadingIndicator];
        // Handle error here
    }];

   [self.operation start];
}