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how to create custom layout in collectionview in ios

https://www.raywenderlich.com/164608/uicollectionview-custom-layout-tutorial-pinterest-2

https://www.raywenderlich.com/156794/custom-uicollectionviewlayout-tutorial-parallax

http://zappdesigntemplates.com/collectionview-flow-layout-from-grid-to-list-layout/