Showing Cells in UICollectionViewController - ios

Question

I have tried to make a UICollectionViewController where I can show a image for each cell. When I want to open this ViewController it shows me an error
import UIKit
private let reuseIdentifier = "Cell"
class RodelCollectionViewController: UICollectionViewController {
var personService: PersonService!
override func viewDidLoad() {
super.viewDidLoad()
assert(personService != nil, "Person Service has to be set, otherwise this class can't do anything useful.")
// Uncomment the following line to preserve selection between presentations
// self.clearsSelectionOnViewWillAppear = false
// Register cell classes
self.collectionView!.registerClass(UICollectionViewCell.self, forCellWithReuseIdentifier: reuseIdentifier)
// Do any additional setup after loading the view.
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
// MARK: - Table view data source
override func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
return 1
}
override func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return personService.allPersons().count
}
override func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCellWithReuseIdentifier("PersonCollectionCell", forIndexPath: indexPath)
if let rodelCollectionViewCell = cell as? RodelCollectionViewCell {
rodelCollectionViewCell.personView?.person = personService.allPersons()[indexPath.item]
}
return cell
}
// MARK: - Navigation
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if let PersonDetailViewController = segue.destinationViewController as? PersonDetailViewController,
let person = (sender as? RodelCollectionViewCell)?.personView?.person {
PersonDetailViewController.person = person
}
}
This is the error
I have tried a lot to fix it but it allways shows me the same error. I don't know where I have to solve this

Answer 1

Did you assign the cell identifier ("PersonCollectionCell") to the cell in the xib file or in the storyboard?
I noticed you declared private let reuseIdentifier = "Cell" that you use to register the cell. But you are using a different reuseIdentifier "PersonCollectionCell" when dequeuing the cell.
Also,
I wouldn't recommend using a function personService.allPersons() inside:
override func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell
This method gets called every time a cell will be reuse/dequeued and could bring performance issues in the future. Instead I would save the result inside an array and update it every time something change and can affect what personService.allPersons() returns.
I would declared a lazy variable like this:
private lazy var allPersons: [WhateverTheTypeIs] = {
let allPersons = self.personService.allPersons()
return allPersons
}
and in the collectionView datasource methods use allPersons instead of the method itself.
Hope this helps.

Answer 2

Another problem which is found with your code is in the
self.collectionView!.registerClass(UICollectionViewCell.self, forCellWithReuseIdentifier: reuseIdentifier)
Here you are trying to register a default UICollectionViewCell and in the cellForItemAtIndexPath you are trying to check for the
if let rodelCollectionViewCell = cell as? RodelCollectionViewCell {
rodelCollectionViewCell.personView?.person = personService.allPersons()[indexPath.item]
}
Here in this code you are checking for your custom cell how this cell become custom cell
if you want to register and create your custom cell your should be like this:
At viewDidLoad()
self.collectionView!.registerClass(RodelCollectionViewCell.self, forCellWithReuseIdentifier: reuseIdentifier)
At cellForItemAtIndexPath
let cell = collectionView.dequeueReusableCellWithReuseIdentifier(reuseIdentifier, forIndexPath: indexPath) as! RodelCollectionViewCell
Default cell
If you want to keep the default cell your code will remain same as it's currently but it will not go inside the condition of custom cell the cell may be show empty if you don't do anything else in the cellforrow
Update
Put both of the code in the cellForItemAtIndexPath
To change cell background color
cell.contentView.backgroundColor = UIColor.redColor()
As person view is coming nil for now as testing purpose we can add a sample view
override func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCellWithReuseIdentifier("PersonCollectionCell", forIndexPath: indexPath)
if let rodelCollectionViewCell = cell as? RodelCollectionViewCell {
rodelCollectionViewCell.personView?.person = personService.allPersons()[indexPath.row]
}
cell.contentView.backgroundColor = UIColor.redColor()
let lbl = UILabel(frame:CGRectMake(0,0,100,21))
lbl.text = "\(indexPath.row)" //replace this value with your original value if it displays for the first time
cell.contentView.addSubview(lbl)
return cell
}