Two Collection Views with Different Reuse Cells in One View Controller - ios

Question

In my view controller I want to have two collection views. After trying this, I got a Sigabrt Error and my app crashes. I am predicting that the problem is because I am assigning the datasource of these collection views to self. I can be wrong, here is my code:
In view did load, i set the datasource of the collection views:
#IBOutlet var hashtagCollectionView: UICollectionView!
#IBOutlet var createCollectionView: UICollectionView!
override func viewDidLoad() {
super.viewDidLoad()
createCollectionView.dataSource = self
hashtagCollectionView.dataSource = self
}
Then I create an Extension for the UICollectionViewDataSource
extension CategoryViewController: UICollectionViewDataSource {
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
var returnValue = 0
if collectionView == hashtagCollectionView {
// Return number of hashtags
returnValue = hashtags.count
}
if collectionView == createCollectionView {
// I only want 3 cells in the create collection view
returnValue = 3
}
return returnValue
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
var return_cell: UICollectionViewCell
// Place content into hashtag cells
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "hashtagCell", for: indexPath) as! TrendingTagsCollectionViewCell
cell.hashtagText = hashtags[indexPath.row]
// Place content in creators cell
let createCell = collectionView.dequeueReusableCell(withReuseIdentifier: "createCell", for: indexPath) as! CreateCollectionViewCell
createCell.text = creators[indexPath.row]
createCell.image = creatorImages[indexPath.row]
// Is this the right logic?
if collectionView == hashtagCollectionView {
return_cell = cell
} else {
return_cell = createCell
}
return return_cell
}
}

Answer 1

This is crashing because your if statement in collectionView(_:cellForItemAt:) doesn't quite cover enough ground.
While you're right that you need to return a different cell based on what collection view is asking, you can't call dequeueReusableCell(withReuseIdentifier:for:) twice with different identifiers like that. Since you ask the same collection view both times, it's very likely that one of the identifiers isn't registered with that collection view.
Instead, you should expand the if to cover just about the entirety of that method:
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
if collectionView == hashtagCollectionView {
// Place content into hashtag cells
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "hashtagCell", for: indexPath) as! TrendingTagsCollectionViewCell
cell.hashtagText = hashtags[indexPath.row]
return cell
} else if collectionView == createCollectionView {
// Place content in creators cell
let createCell = collectionView.dequeueReusableCell(withReuseIdentifier: "createCell", for: indexPath) as! CreateCollectionViewCell
createCell.text = creators[indexPath.row]
createCell.image = creatorImages[indexPath.row]
return cell
} else {
preconditionFailure("Unknown collection view!")
}
}
That only tries to dequeue a cell once, depending on which collection view is asking, and casts the returned cell to the right class.
N.B. This kind of approach works for awhile, but in the long run, you can get very long UICollectionViewDataSource method implementations, all wrapped up in a series of if statements. It might be worth considering separating out your data sources into separate smaller classes.

Answer 2

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
if let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "hashtagCell", for: indexPath) as? TrendingTagsCollectionViewCell {
cell.hashtagText = hashtags[indexPath.row]
return cell
}
if let createCell = collectionView.dequeueReusableCell(withReuseIdentifier: "createCell", for: indexPath) as? CreateCollectionViewCell {
createCell.text = creators[indexPath.row]
createCell.image = creatorImages[indexPath.row]
return createCell
}
return UICollectionViewCell() // or throw error here
}

Answer 3

I think your code crash with a nil when reuse cell
You should test cellForItemAt like this
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
if collectionView == hashtagCollectionView {
// Place content into hashtag cells
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "hashtagCell", for: indexPath) as! TrendingTagsCollectionViewCell
cell.hashtagText = hashtags[indexPath.row]
return cell
} else {
// Place content in creators cell
let createCell = collectionView.dequeueReusableCell(withReuseIdentifier: "createCell", for: indexPath) as! CreateCollectionViewCell
createCell.text = creators[indexPath.row]
createCell.image = creatorImages[indexPath.row]
return createCell
}
}