CollectionViewFlowLayout Issue - objective-c

Question

when I am adding UICollectionViewFlowLayout file with collection view. collectionViewCell height is not increasing according to the collection view. it takes spacing from the top and bottom:
- (void)awakeFromNib
{
[super awakeFromNib];
self.itemSize = CGSizeMake((self.collectionView.frame.size.width/2)+100,self.collectionView.frame.size.height );
//self.minimumInteritemSpacing = 10.0;
self.minimumLineSpacing = 10.0;
self.scrollDirection = UICollectionViewScrollDirectionHorizontal;
self.sectionInset = UIEdgeInsetsMake(0, 30.0, 0, 30.0);
}
- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity {
NSInteger itemsCount = [self.collectionView.dataSource collectionView:self.collectionView numberOfItemsInSection:0];
// Imitating paging behaviour
// previous offset and scroll direction
if ((self.previousOffset > self.collectionView.contentOffset.x) && (velocity.x < 0.0f)) {
self.currentPage = MAX(self.currentPage - 1, 0);
} else if ((self.previousOffset < self.collectionView.contentOffset.x) && (velocity.x > 0.0f)) {
self.currentPage = MIN(self.currentPage + 1, itemsCount - 1);
}
// Update offset by using item size + spacing
CGFloat updatedOffset = (self.itemSize.width + 5) * self.currentPage;
self.previousOffset = updatedOffset;
return CGPointMake(updatedOffset, proposedContentOffset.y);
}
i have created sub class of UICollectionViewLayout.