Now that we are maintaining a list of photos, we need to display it in our collection view. A collection view is populated by providing it with a data source that implements its UICollectionViewDataSource protocol. Probably the most common thing to do is to have the view controller be the data source. We can do this by opening the Main.storyboard back up and control dragging from the collection view to the view controller:
When you let go, select dataSource from the menu. After that, all we need to do is implement the data source protocol. The two methods we need to implement are collectionView:numberOfItemsInSection: and collectionView:cellForItemAtIndexPath:. The former allows us to specify how many cells should be displayed and the latter allows us to customize each cell for a specific index into our list. It is easy for us to return the number of cells that we want:
extension ViewController: UICollectionViewDataSource {
func collectionView(
collectionView...