The Summary of the UICOllectionView

参考网络教程，自己总结而来

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* UICollectionViewCustomLayout

 1. Core Layout Process(核心布局的处理过程)
	继承UICollectionViewLayout必须实现如下方法：
		- prepareLayout():
			 布局将要生效在方法里面计算好item的position，collection的size
		- collectionViewContentSize()
			 返回CollectionViewContentSize 不是size(width,height)，contentSize一般比size要大 
		- layoutAttributeForElementsInRect()
			 返回特定区域内的布局属性
 2. Calculating Layout Attributes(计算 布局的属性)
 	cell 宽度不变，变高度 ，高度（caption，comment，image.size.height）	

* UICollectionViewFlowLayout

eg 1. FlickrSearch

eg 2. Photomania

eg 3. UICollectionFlowLayout

eg 4. UICollectionViewDelegateFlowLayout

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1. 基本概念: UICollectionView
   • UICollectionCell
   • Supplementary Views
   • Decoration Views(using custom layout)

Layouts can be swapped out during runtime and the collection view can even automatically animate switching from one layout to another!

2. UICollectionViewDelegateFlowLayout
   • sizeForItemAtIndexPath -> CGSize
   • insetForSectionAtIndex -> UIEdgeInsets
   • minimumLineSpacingForSectionAtIndex ->CGFloat
   • minimumInteritemSpacingForSectionAtIndex ->CGFloat
   • referenceSizeForHeaderInSection ->CGSize
   • referenceSizeForFooterInSection ->CGSize