http://www.oschina.net/question/54100_27841
启动：onCreate()->onStart()->onResume
当从Activity界面直接按Back键，onPause()->onStop()->onDestory()
当从Activity界面按home键。onPause()->onStop()，
接着再进入Activity时onRestart()->onStart()->onResume()
public class Activity extends ApplicationContext { protected void onCreate(Bundle savedInstanceState); protected void onStart(); protected void onRestart(); protected void onResume(); protected void onPause(); protected void onStop(); protected void onDestroy(); }