Selecting Objects from NSArray for further deleting with an IBAction - objective-c

Question

So I am trying to select objects from my array, to be able to delete them when I do an IBAction. I tried:
checking if the item is Selected:
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
if (self.editEnabled) {
RDNote *selectedNote = [self.notes objectAtIndex:indexPath.row];
if (selectedNote.isSelected) {
selectedNote.selected = NO;
for (NSIndexPath *indexPathFromArray in self.indexPathsOfSelectedCells) {
if (indexPathFromArray.row == indexPath.row) {
[self.mutableCopy removeObject:indexPathFromArray];
}
}
} else {
selectedNote.selected = YES;
[self.indexPathsOfSelectedCells addObject:indexPath];
}
[self.collectionView reloadData];
IBAction:
- (IBAction)didTapTrashBarButton:(id)sender {
NSMutableArray *mutableNotes = [NSMutableArray arrayWithArray:self.notes];
for (NSIndexPath *indexPath in self.indexPathsOfSelectedCells) {
[mutableNotes removeObjectAtIndex:indexPath.row];
}
self.notes = [NSArray arrayWithArray:mutableNotes];
[self.collectionView performBatchUpdates:^{
[self.collectionView deleteItemsAtIndexPaths:[NSArray arrayWithArray:self.indexPathsOfSelectedCells]];
} completion:^(BOOL finished) {
self.indexPathsOfSelectedCells = nil;
[self activateEditMode:NO];
[self saveDataToFile:self.notes];
}];
}
But I am having issues with indexes e.g.:(some times shows me the Error that Object index 2 is not between [0..1]), and there are bugs while selecting multiple Object and Deleting them.
Please help me with an advice for some other method that I can use, a Code will be perfect! Thanks!

Answer 1

This problem arrises because:
Let say you have five objects in array 1,2,3,4,5
you are running a loop for removing object based on indexpath which are selected rows. Now your indexpath contains 1st row and 3rd row.
while executing it for the first time you will remove object 1. Now 2,3,4,5 will left in the array. Now second time your indexpath.row is 3rd. It will remove third object which is 4 but in actual array it was 3.
Your code is crashing sometimes because if you have selected first row and last row. In this case i have selected 1 and 5. Now my indexpaths array will say I have to delect objectsAtIndexes 1 and 5.
While executing the loop I'll remove object at Index 1. Now i will be left with 2,3,4,5. On second iteration it will say remove objectAtIndex 5 where as Index 5 doesn't exist because now we have 4 elements in array.
In such cases best way of doing this is try removing elements in array from the end like remove 5th element first and then go for other one. Run your loop in reverse order.
NSInteger i = [self.indexPathsOfSelectedCells count]-1;
while (i > 0){
NSIndexPath *indexPath = [self.indexPathsOfSelectedCells objectAtIndex:i];
[mutableNotes removeObjectAtIndex:indexPath.row];
i--;
}