How to make UICollectionViewFlowLayout itemSize dynamic for screen size

Question

I am working programmatically (no storyboard) and am having trouble making layout.itemSize dynamic for different screen sizes. I get this error message:

Answer 1

Need to use the flow delegate method:

- (CGSize)collectionView:(UICollectionView *)collectionView
                  layout:(UICollectionViewLayout *)collectionViewLayout
  sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    CGSize cellSize = CGSizeMake(width, height);

    return cellSize;
}

You specify the width and height float values to whatever you want.

For example, lets say your CollectionView is vertical and you want a short header view, a big middle view and a small footer view, then you could do something like:

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

    cellSize.width = self.view.bounds.size.width;

    if(indexPath.row == 0)
    {
        // header view height
        cellSize.height = 100;
    }
    else if(indexPath.row == 1)
    {
        // body view height
        cellSize.height = 500;
    }
    else
    {
        // assuming number of items is 3, then footer view is last view
        // footer view height
        cellSize.height = 100;
    }

    return cellSize;
}