UICollectionView layoutAttributesForElementsInRect not returning reusableViews

Question

I am trying to implement a UICollectionView using supplementaryViews. I use a Nib file to create my supplementary view. Here is the method in the layout to add the supplementaryView:

    NSMutableArray *attributesInRect = [[super layoutAttributesForElementsInRect:rect] mutableCopy];

NSLog(@"%@", attributesInRect);
if ([self.collectionView numberOfItemsInSection:0] > 1 && !self.selectedItem)
{
    if ([self.musicList count] > 0)
    {
        UICollectionViewLayoutAttributes *musicViewAttributes = [self layoutAttributesForSupplementaryViewOfKind:@"MusicView" atIndexPath:[NSIndexPath indexPathForRow:1 inSection:0]];

        musicViewAttributes.size = CGSizeMake(CGRectGetWidth([[UIScreen mainScreen] bounds]), 150);
        musicViewAttributes.center = CGPointMake(musicViewAttributes.size.width/2, musicViewAttributes.size.height/2);
        musicViewAttributes.zIndex = 0;
        [attributesInRect addObject:musicViewAttributes];
    }
}
return attributesInRect;

Don't pay attention to the conditions here, only on the array of attributes (attributesInRect). When I do that, my supplementary is properly added to the CollectionView.

My problem is to retrieve an added supplementaryView. On the NSLog, it seams that my supplementaryView is not listed in the array. In this case I can't check it's existence before adding a new one.

I don't really understand why as the documentation specify:

Return Value An array of UICollectionViewLayoutAttributes objects representing the layout information for the cells and views. The default implementation returns nil.

According to that my supplementaryView should be in that array.

Any idea about that ?