Now the collection view asks the layout wether it should invalidate, before actually changing the frame or bounds.
Now the collection view asks the layout wether it should invalidate, before actually changing the frame or bounds.

ba01ei/PSTImprovedCollectionView,jianwoo/PSTCollectionView,steipete/PSTCollectionView,Kevin775263419/PSTCollectionView,godLoveLucifer/PSTCollectionView,CorzFree/PSTCollectionView,zace-yuan/PSTCollectionView,zjh171/PSTCollectionView,Anish-kumar-dev/PSTCollectionView,niuxinghua/PSTCollectionView