title: Calc UICollectionViewCell height while downloading image from internet
body: <p>I want to create a water fall layout using CHTCollectionViewWaterfallLayout. I noticed in the demo the cell height is fixed and it's in an array. But, Right now, I got a image url and I want to show it on the screen, but the height is not knowing. So, heightForItemAtIndexPath datasource is not working. How to calc the height of some image url before it's downloaded. Or can I downloading and displaying the image in the cellForItemAtIndexPath datasource method while calc the height and set the cell height in the heightForItemAtIndexPath datasource method? How to do that?</p>