iOS Assertion Failure in UICollectionView

Question

I'm getting the error ...

*** Assertion failure in -[UICollectionView _dequeueReusableViewOfKind:withIdentifier:forIndexPath:], /SourceCache/UIKit/UIKit-2372/UICollectionView.m:2249

When trying to display a UICollectionView.

The lines causing it are...

static NSString *CellIdentifier = @"Cell";

UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath];

Error happening on the dequeue.

There are no other errors so I'm struggling to know where to begin with this.

Can anyone shed light on this?

Answer 1

I have seen this error pop up when using multiple UICollectionViews with unique ReuseIdentifiers. In ViewDidLoad you want to register each CollectionView's reuseIdentifier like so:

[_collectionView1 registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"collectionView1CellIdentifier"];
[_collectionView2 registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"collectionView2CellIdentifier"];

Then when you get to "- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath" you want to make sure that you don't try to set a cell for collectionView1 to the reuseIdentifier for collectionView2 or you will get this error.

DON'T DO THIS: (Or collectionView2 will see the wrong Identifier and throw a fit before seeing the identifier it was expecting)

UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"collectionView1CellIdentifier" forIndexPath:indexPath];

if(collectionView != _collectionView1){
   cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"collectionView2CellIdentifier" forIndexPath:indexPath];
}

cell.backgroundColor = [UIColor greenColor];
return cell;

DO THIS:

UICollectionViewCell *cell;

if(collectionView == _collectionView1){
    cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"collectionView1CellIdentifier" forIndexPath:indexPath];
}else{
   cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"collectionView2CellIdentifier" forIndexPath:indexPath];
}

cell.backgroundColor = [UIColor greenColor];
return cell;