1. 视图控制对象应该在什么时候载入视图？
When the view controller receive the view message, the view controller begin to creat the view, if the veiw object does not exist.
If you send the message of view in view controller init method, this leads the pattern deferred mechanism does not work。
This problem is seem not serious, but this situation is very serious when considering low memory warnings.
2. when syetem is not much memory to use, the system will send low memmory warnings. Receiving the warning, release the not use, and easy rebulit resourece.