UICollectionView update a single cell

Question

- (void)reloadItemsAtIndexPaths:(NSArray *)indexPaths

Here it is a method to reload the specific indexPaths in your collectionView

Dinesh's answer is spot-on. But to avoid unwanted animations when reloading (aka "flashing") use:

BOOL animationsEnabled = [UIView areAnimationsEnabled];
[UIView setAnimationsEnabled:NO];
[myCollectionView reloadItemsAtIndexPaths:myIndexPaths];
[UIView setAnimationsEnabled:animationsEnabled];

See Inserting, Deleting, and Moving Sections and Items from the "Collection View Programming Guide for iOS":

To insert, delete, or move a single section or item, you must follow these steps:

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Update the data in your data source object. Call the appropriate method of the collection view to insert or delete the section or item. It is critical that you update your data source before notifying the collection view of any changes. The collection view methods assume that your data source contains the currently correct data. If it does not, the collection view might receive the wrong set of items from your data source or ask for items that are not there and crash your app.

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So in your case, you must add an image to the collection view data source first and then call insertItemsAtIndexPaths. The collection view will then ask the data source delegate function to provide the view for the inserted item.