Using Swift to Immediately Update UICollectionView with API Result

November 25, 2014

I was puzzled a few days ago when the UICollectionView I was looking at didn’t automatically get updated even after calling reloadData(). After much googling, I found this post in stackoverflow which explained what caused it.

It wasn’t because my API was slow nor was it because of some Swift issue I wasn’t aware of. It was because the task was added in a background queue. To fix this, you just need to make sure that the block you want to get updated immediately was running on the main thread.

This was resolved by wrapping reloadData() in a dispatch_async with the queue for the main thread passed as the argument. We can retrieve the main thread queue through dispatch_get_main_queue.

dispatch_async(dispatch_get_main_queue(), {

After adding that, my UICollectionView gets updated immediately after receiving the result from the API.

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