UICollectionView update a single cell

Question

I am attempting to update a single cell inside a UICollectionView , specifically I am just trying to update an image in that specific cell detonated by cell.imageView . [self.collectionView reloadData] is not really an option because it makes the whole collection view flash. [self.collectionView beginUpdates] is not a thing in a UICollectionView it seems.

I understand I may be able to use:

[self.collectionView performBatchUpdates:^{
    //do something
} completion:nil];

I am not exactly sure what to put inside a completion block to update that certain cell's imageView . This is all being done inside of didSelectItemAtIndexPath .Also I am not using NSFetchedResultsController . Any ideas?

Answer 1

- (void)reloadItemsAtIndexPaths:(NSArray *)indexPaths

这是一个在collectionView重新加载特定indexPaths的方法

Answer 2

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];

Answer 3

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.