android fragment执行流程
1. onAttach ------called once the fragment is associated with its activity
2. onCreate-------called to do initial creation of the fragment
3. onCreateView---creates and returns the view hierarchy associated with the fragment
4.onActivityCreated ---tells the fragment that its activity has completed its own {@link Activity#onCreate Activity.onCreaate}
5.onStart----------makes the fragment visible to the user (based on its containing activity being started)
6.onResume-----makes the fragment interacting with the user (based on its containing activity being resumed).
7. onPause----- fragment is no longer interacting with the user either because its activity is being paused or a fragment operation is modifying it in the activity.
8.onStop------fragment is no longer visible to the user either because its activity is being stopped or a fragment operation is modifying it in the activity.
9.onDestroyView ------allows the fragment to clean up resources associated with its View.
10.onDestroy---------called to do final cleanup of the fragment's state.
11.onDetach--------called immediately prior to the fragment no longer being associated with its activity