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Trying to remove the objects from NSMutableArray, below is how addition done to array.

sectionInfo = [self.collectionView indexPathsForSelectedItems];

How tried to remove

[sectionInfo removeAllObjects];

The error i got is unrecognized selector sent to instance 0x169cfb70. I think it's because i didn't added items in to array ass addObject: but that's not my requirement. So, how to manage this.

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Is section info is an NSMutable array? – Augustine P A May 27 at 5:43

3 Answers

up vote 1 down vote accepted

The indexPathsForSelectedItems returns an immutable NSArray, regardless of how sectionInfo was declared. Theoretically you could do:

sectionInfo = [[self.collectionView indexPathsForSelectedItems] mutableCopy];

Or, if you're just trying to reset sectionInfo, you can leave the declaration of sectionInfo alone, but then rather than removeAllObjects, you could simply say:

sectionInfo = nil;

Or create a new array:

sectionInfo = [NSMutableArray array];

I guess it comes down to why you're trying to remove objects from sectionInfo, rather than just resetting it.

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up vote 3 down vote

The problem is that -[UICollectionView indexPathsForSelectedItems] doesn't return a NSMutableArray. You want to convert it to a NSMutableArray before trying to modify it:

sectionInfo = [NSMutableArray arrayWithArray: [self.collectionView indexPathsForSelectedItems]];
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up vote 0 down vote

Make a mutable copy of the indexPathsForSelectedItems . Because indexPathsForSelectedItems returns NSArray not NSMutableArray. NSArray doesn't have removeAllObjects method. 

sectionInfo = [[self.collectionView indexPathsForSelectedItems]mutableCopy];
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