The sample code is modified from http://easymorse-iphone.googlecode.com/svn/trunk/changeViewController, the original author is marcus wang, his blog is http://wangjun.easymorse.com/?p=1630. I change his sample code a little to watch the view load and unload event when receiving memory warning. I also have a blog to introduce the new APIs about UIViewController on iOS5, it is from http://blog.devtang.com/blog/2012/02/06/new-methods-in-uiviewcontroller-of-ios5/