集合视图分页IOS

Question

I want to apply a pagnination on collectionView such that if items are less than equal to 4,the collectionView reloads the data. I tried but result is not approppriate, all cells are loaded for the first time and when scroll ended, it terminates the app, as I incremented the cell items to 1, so it terminates the app.

How can I load only 4 cells for the first time and then after scrolling reload the remaining.

My ViewController Code:

NSInteger _currentPage;
@property (nonatomic, retain) NSMutableArray *items;

MY CODE:

#define ITEMS_PAGE_SIZE 4
#define ITEM_CELL_IDENTIFIER @"Cell"
#define LOADING_CELL_IDENTIFIER @"LoadingItemCell"
- (void)viewWillAppear:(BOOL) animated

{
 UICollectionViewFlowLayout *collectionViewLayout = (UICollectionViewFlowLayout*)self.collectionView.collectionViewLayout;
    collectionViewLayout.sectionInset = UIEdgeInsetsMake(20, 0, 20, 0);
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
    return arr.count+1;
}

    - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
        Data* d = arr[indexPath.row];
           if (indexPath.item < arr.count) {
               UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:ITEM_CELL_IDENTIFIER forIndexPath:indexPath];

               UILabel *label = (UILabel *)[cell viewWithTag:200];
               label.text = [NSString stringWithFormat:@"%@",d.detail];
               return cell;
        } else {
            NSLog(@"FETCHING MORE ITEMS ******************");

            // Generate the 'next page' of data.
            NSMutableArray *newData = [NSMutableArray array];
            NSInteger pageSize = ITEMS_PAGE_SIZE;
            for (int i = _currentPage * pageSize; i < ((_currentPage * pageSize) + pageSize); i++) {
                [newData addObject:[NSString stringWithFormat:@"Item #%d", i]];
            }

            _currentPage++;


            // Simulate an async load...

            double delayInSeconds = 3;
            dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
            dispatch_after(popTime, dispatch_get_main_queue(), ^(void){

                // Add the new data to our local collection of data.
                for (int i = 0; i < newData.count; i++) {
                    [self.items addObject:newData[i]];
                }

                // Tell the collectionView to reload.
                [self.collectionView reloadData];

            });
        }
        UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:LOADING_CELL_IDENTIFIER forIndexPath:indexPath];

        UIActivityIndicatorView *activityIndicator = [[UIActivityIndicatorView alloc]
                                                      initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
        activityIndicator.center = cell.center;
        [cell addSubview:activityIndicator];

        [activityIndicator startAnimating];

        return cell;

    }

Answer 1

When asked for the cell you are getting your data out of your array before you check if the supplied index is valid. This line should be moved inside the if statement to be safe.