单元未添加到集合视图

Question

I'm trying to add a collection view cell as and when the user chooses to do so. he does this in a separate view controller where he gives the name and saves it. but when it returns back to the initial view controller the new cell doesn't get added to the collection view.

Here is my code for the 2 view controllers :

import UIKit

class FlashViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

@IBOutlet var collectionView: UICollectionView!

var decks: [Deck] = []

    override func viewDidLoad() {
    super.viewDidLoad()
    // Move on ...
    let layout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()
    layout.sectionInset = UIEdgeInsets(top: 75, left: 20, bottom: 10, right: 20)
    layout.itemSize = CGSize(width: 150, height: 200)
    collectionView = UICollectionView(frame: self.view.frame, collectionViewLayout: layout)
    self.collectionView.dataSource = self
    self.collectionView.delegate = self
    collectionView.registerClass(DeckCollectionViewCell.self, forCellWithReuseIdentifier: "DeckCollectionViewCell")
    collectionView.backgroundColor = UIColor.whiteColor()
    self.view.addSubview(collectionView!)

    var deck1 = Deck()
    deck1.name = "SAT is the bomb"
    self.decks.append(deck1)

}

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


func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
    var cell = collectionView.dequeueReusableCellWithReuseIdentifier("DeckCollectionViewCell", forIndexPath: indexPath) as DeckCollectionViewCell
    cell.backgroundColor = UIColor.blackColor()
    cell.textLabel?.text = "\(indexPath.section):\(indexPath.row)"
    cell.imageView?.image = UIImage(named: "circle")
    return cell
}


override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    var nextViewController = segue.destinationViewController as NewDeckViewController
    nextViewController.deckCollection = self
}
}

Next view controller :

import UIKit

class NewDeckViewController : UIViewController
{
@IBOutlet weak var deckNameTextField: UITextField!

var deckCollection = FlashViewController()

override func viewDidLoad() {
    super.viewDidLoad()
    // Move on...
}

@IBAction func cancelTapped(sender: AnyObject) {
    self.dismissViewControllerAnimated(true, completion: nil)
}

@IBAction func createTapped(sender: AnyObject) {
    var newDeck = Deck()
    newDeck.name = self.deckNameTextField.text
    self.deckCollection.decks.append(newDeck)
    self.dismissViewControllerAnimated(true, completion: nil)
}


}

Answer 1

You need to reload the collection view

self.collectionView.reloadData

Or alternatively you can use reloadItemsAtIndexPath if you don't want to reload the entire collection view / want to show an animation, assuming you know the indexPath of the new item.

Now the question is, when do you call this?

Easiest thing for your current implementation is in viewWillAppear , but that will also reload you collection view when it does not need to be reloaded (eg. the first time the view appears, or if the next view controller returns without appending anything etc -- not a huge deal if your collection view is small, but it can easily be done better). You could also call it from the second view controller right after the append, although this isn't so clean either. You could also implement a method inside your collection view controller that is called by the next view controller whenever it wants to append something that includes the item you want to add as a parameter instead of directly adding it to the other controller's array.

Retaining a reference to the presenting view controller and accessing its data directly is also not good practice. What you really should be using is a delegate method (which is similar to the suggestion above, except more flexible since the other view controller doesn't need to know anything about its delegate other than that it implements the delegate protocol). More info here