nib文件的默认搜索规则

　　if you do not specify a nib name, and do not override the loadView method in your custom subclass, the view controller searches for a nib file using other means. Specifically, it looks for a nib file with an appropriate name (without the .nib extension) 

1. If the view controller class name ends with the word ‘Controller’, as in MyViewController, it looks for a nib file whose name matches the class name without the word ‘€œController’, as in MyView.nib.

2. It looks for a nib file whose name matches the name of the view controller class. For example, if the class name is MyViewController, it looks for a MyViewController.nib file.