UICollectionView delegate method cellForItemAtIndexPath:indexPath not called from sizeForItemAtIndexPath

cocoa-touch, ios, ios6, objective-c, uicollectionview

Solution

I ended up with a Class method instead of an instance method:

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {

    return [CustomCell preferredSizeWithData:self.data[indexPath.row]; 

}

I made a Class method for the cell... to this method I provide the data that an actual instance at the specified `indexPath` would hold and calculate the preferred size

I think that

CustomCell * cell = (CustomCell *)[collectionView cellForItemAtIndexPath:indexPath];

triggers internally

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath

and what we see is some mechanism from Apple to prevent a loop cycle... because calling directly

CustomCell * cell = (CustomCell *)[self collectionView:collectionView cellForItemAtIndexPath:indexPath];

results in a loop cycle.

Problem

When I call ``` [collectionView cellForItemAtIndexPath:indexPath:] ``` from inside ``` [collectionView:layout:sizeForItemAtIndexPath:] ``` then the delegate method is not triggered. Any idea why not? You can see it here. ``` - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath { CustomCell *cell = [self.collectionView dequeueReusableCellWithReuseIdentifier:@"CustomCell" forIndexPath:indexPath]; [cell configureWithData:self.data[indexPath.row]]; return cell; } - (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath { CustomCell * cell = (CustomCell *)[collectionView cellForItemAtIndexPath:indexPath]; return [cell preferredSize]; } ``` What I want to do is to ask the cell for its preferred size. I could do ``` CustomCell * cell = (CustomCell *)[self collectionView:collectionView cellForItemAtIndexPath:indexPath]; ``` but then a never-ending loop cycle is triggered why is its delegate method not called as it should be?

Original source