Loading UICollectionViewCell one at a time

Question

As per this article http://aplus.rs/2014/how-to-animate-in-uicollectionview-items/ I am trying to load a UICollectionViewCell one at a time to animate the cell when it appears. However, when I call the code the loops the cellCount++, it produces this error:

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid update: invalid number of items in section 0. The number of items contained in an existing section after the update (1) must be equal to the number of items contained in that section before the update (1), plus or minus the number of items inserted or deleted from that section (1 inserted, 0 deleted) and plus or minus the number of items moved into or out of that section (0 moved in, 0 moved out).'

And I cannot for the life of me figure it out.

Here is my code:

-(void)addCells{

    for (self.cellCount=0; self.cellCount<50; self.cellCount++) {

        [self.collectionView performBatchUpdates:^{
            [self.collectionView insertItemsAtIndexPaths:[NSArray arrayWithObject:[NSIndexPath indexPathForItem:self.cellCount inSection:0]]];
        } completion:nil];

    }

}

rdelmar rdelmar · Accepted Answer · 2014-11-08T06:20:08

You can do this using a timer, whose action method adds objects from your data source array to a mutable array that you use to populate your collection view.

-(void)viewDidLoad {
    [super viewDidLoad];
    self.mutableArray = [NSMutableArray new];
    self.data = @[@"one", @"one", @"one", @"one", @"one", @"one"];
    [NSTimer scheduledTimerWithTimeInterval:.1 target:self selector:@selector(addCells:) userInfo:nil repeats:YES];
}

-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    return self.mutableArray.count;
}


-(void)addCells:(NSTimer *) timer {
    static int counter = 0;
    [self.mutableArray addObject:self.data[counter]];
    counter ++;
    [self.collectionview insertItemsAtIndexPaths:@[[NSIndexPath indexPathForItem:self.mutableArray.count -1 inSection:0]]];
    if (self.mutableArray.count == self.data.count) {
        [timer invalidate];
    }
}

Loading UICollectionViewCell one at a time

2 Answers