从程序的log来看：
2012-10-19 15:51:44.811inHyron[483:b903] init
2012-10-19 15:51:54.081inHyron[483:b903] viewDidLoad
2012-10-19 15:51:54.082inHyron[483:b903] viewVillAppear
2012-10-19 15:51:54.084 inHyron[483:b903] viewDidAppear
很明显，先执行init、然后执行viewDidLoad，然后是viewWillAppear最后是viewDidAppear，这样视图就创建好了，当视图消失或者被覆盖的时候：
2012-10-19 15:54:14.557inHyron[483:b903] viewWillDisappear
2012-10-19 15:54:14.558inHyron[483:b903] viewDidDisappear
这样一来视图就消失了，当模拟内存警告的时候：
2012-10-19 15:55:14.333inHyron[483:b903] Received simulated memory warning.
2012-10-19 15:55:14.334inHyron[483:b903] viewWillUnload
2012-10-19 15:55:14.335 inHyron[483:b903]viewDidUnload
