objective c blocks - Reloading a UICollectionView using reloadData method returns immediately before reloading data

Question

I need to know when reloading a UICollectionView has completed in order to configure cells afterwards (because I am not the data source for the cells - other wise would have done it already...)

I've tried code such as

[self.collectionView reloadData];
[self configure cells]; // BOOM! cells are nil

I've also tried using

[self.collectionView performBatchUpdates:^{
  [self.collectionView reloadData];
    } completion:^(BOOL finished) {
        // notify that completed and do the configuration now
  }];

but when I reload the data I am getting crashes.

How can I reload the data into the collection, and only when it has finished reloading - do a particular completion handler

Answer 1

This is caused by cells being added during layoutSubviews not at reloadData. Since layoutSubviews is performed during next run loop pass after reloadData your cells are empty. Try doing this:

[self.collectionView reloadData];
[self.collectionView layoutIfNeeded];
[self configure cells]; 

I had similar issue and resolved it this way.