UICollectionView Header

헷갈리는 거 저장용,,

1. UICollectionReusableView Xib 만들기

2. Xib register하기

self.medalCollectionView.register(UINib(nibName: Const.Xib.Name.medalCollectionReusableView, bundle: nil), forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: Const.Xib.Identifier.medalCollectionReusableView)

cell xib register할 때와는 다르게

medalCollectionView.register(<#T##viewClass: AnyClass?##AnyClass?#>, forSupplementaryViewOfKind: <#T##String#>, withReuseIdentifier: <#T##String#>)

이 메서드를 사용해서 register 해 줘야 한다.
kind는 elementKindSectionHeader 로!

3. viewForSupplementaryElementOfKind

func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
                
        if let headerView = collectionView.dequeueReusableSupplementaryView(ofKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: Const.Xib.Identifier.medalCollectionReusableView, for: indexPath) as? MedalCollectionReusableView {
            
            return headerView
        }
        
        return UICollectionReusableView()
}

viewForSupplementaryElementOfKind 함수 내에서 headerview를 반환해주는데,
보통 이 함수 내에서 kind로 switch 문을 통해 분기처리 해준다.

4. referenceSizeForHeaderInSection

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForHeaderInSection section: Int) -> CGSize {
    return CGSize(width: collectionView.frame.width, height: 300)
}

이렇게 height까지 지정해줘야 헤더가 보인다.