iOS Swift：致命错误，在UICollectionView中展开可选

Question

I am trying to create a custom collection view. This is my first time using this view type and also my first time using Swift after a few years hiatus from iOS programming.

Here is the code for the cell:

override func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCellWithReuseIdentifier(reuseIdentifier, forIndexPath: indexPath) as! PrincipalViewCell

    // Configure the cell
    var p: Administrator = principals[indexPath.row]

    cell.name.text = p.name

    return cell
}

I get the following error:

fatal error: unexpectedly found nil while unwrapping an Optional value

on line:

cell.name.text = p.name

I really am at a loss as to why this is happening.

Edit:

As requested here is the full CollectionViewController:

import UIKit

let reuseIdentifier = "PrincipalCell"
var principals = [Administrator]()

class PrincipalViewController: UICollectionViewController, UICollectionViewDelegateFlowLayout {

    override func viewDidLoad() {
        super.viewDidLoad()

        // Uncomment the following line to preserve selection between presentations
        // self.clearsSelectionOnViewWillAppear = false



        // Register cell classes
       // self.collectionView!.registerClass(UICollectionViewCell.self, forCellWithReuseIdentifier: reuseIdentifier)
        self.collectionView!.registerClass(PrincipalViewCell.self, forCellWithReuseIdentifier: reuseIdentifier)

        // Do any additional setup after loading the view.
    }

    override func viewWillAppear(animated: Bool)
    {
        let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
        principals = appDelegate.admins           

        super.viewWillAppear(animated)
        navigationController?.setNavigationBarHidden(false, animated: true)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    /*
    // MARK: - Navigation

    // In a storyboard-based application, you will often want to do a little preparation before navigation
    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        // Get the new view controller using [segue destinationViewController].
        // Pass the selected object to the new view controller.
    }
    */

    // MARK: UICollectionViewDataSource

    override func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
        //#warning Incomplete method implementation -- Return the number of sections
        return 1
    }


    override func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        //#warning Incomplete method implementation -- Return the number of items in the section
        return principals.count
    }

    override func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier(reuseIdentifier, forIndexPath: indexPath) as! PrincipalViewCell

        // Configure the cell
        var p: Administrator = principals[indexPath.row]

        cell.name.text = p.name    

        return cell
    } 
}

in the viewWillAppear I had a println() statement that output the name value for each entry in the array and all 6 appeared, so I know the array was not a nil value there. Also, I tried changing

cell.name.text = p.name

to just

cell.name.text = "test string"

to see if that made a difference and I still got the same error.

Answer 1

The problem may be as per this below scenario.

var p: Administrator = principals[indexPath.row]

If Administrator is a class and it has a property called name, if this property is of optional type and unfortunately if it does not have value it may create the problem. So if this is the case then do as below,

 if let iName = p.name as? String {
        cell.name.text = iName
}

The Administrator class/struct may b defined as

class Administrator {
   var name: String! //or var name: String? 
}

Answer 2

You need to remove the following line in your viewDidLoad() :

self.collectionView!.registerClass(PrincipalViewCell.self, forCellWithReuseIdentifier: reuseIdentifier)

If you are using a storyboard you don't want to call this. It will overwrite what you have in your storyboard.