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register for supplementaryViewimplement the collectionView function for viewForSupplementaryElementOfKindimlement the layoutAttributes for supplementaryViewbut it still not work.where is wrong?besides it is ios 9.0

I created a storyboard then place a UICollectionView in it.And specified the Layout by my custom LayoutView.I want to add a header but the Items "Section Header" disappeared since I specify the Layout.So I create a reuseableView and want to register and use in the CollectionViewI registered it and implemented the viewForSupplementaryElementOfKind function.but the supplementaryView dose not appear.why is it?I searched google and it seems to I have to specify the CGSize of the SupplementaryView but I can not find the func or variable to rewrite.thank you.