heightForRowAtIndexPath: 都计算出来,即使 cell 还没有展示。cell.rowHeight 设置高度,不要再实现tableView:heightForRowAtIndexPath: delegate.There are performance implications to using
tableView:heightForRowAtIndexPath:instead of therowHeightproperty. Every time a table view is displayed, it callstableView:heightForRowAtIndexPath:on the delegate for each of its rows, which can result in a significant performance problem with table views having a large number of rows (approximately 1000 or more). via Apple Document
转载自:http://fann.im/blog/2012/09/11/uitableview-optimization-notes/
原文:http://www.cnblogs.com/Jenaral/p/5122018.html