Data not fully loaded from Core Data when being called by UICollectionView to display cell

Question

I want to display some data in UICollectionView read from Core Data in viewDidLoad. However, when the UICollectionView is presenting its cells, the data has not been fully loaded yet. Thus, the UICollectionView is empty.

What I want to ask is how to make sure the data is ready before the UICollectionView starts to load its cells. Following is part of the code I'm working on.

class MenuViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate {

    @IBOutlet weak var categoryCollectionView: UICollectionView!

    var allDishes = [AnyObject]()
    var categoryList = [String]()

    let context = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.

        let request = NSFetchRequest(entityName: self.dishItemEntityName)
        var allDishes = self.context?.executeFetchRequest(request, error: nil)

        if let allDishes = allDishes {
            for dish in self.allDishes {
                let dish = dish as! DishItem
                if contains(self.categoryList, dish.category) {
                    continue
                } else {
                    self.categoryList.append(dish.category)
                }
            }
        }
    }


    // MARK: Delegate Methods

    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return self.categoryList.count
    }
}

Answer 1

viewDidLoad is called before viewWillAppear . You could call reloadData on the collection view in viewWillAppear .

Better: use a NSFetchedResultsController which will give many other benefits for memory management, performance and automatic updates.

Answer 2

Call reloadData at the end of viewDidLoad

override func viewDidLoad() {
    ...
    categoryCollectionView.reloadData()
}