LifeCycle

Fragment lifecycle is similar to Activity lifecycle

• Lifecycle callbacks define how Fragment behaves in each state

  • States

    • Active(or Resumed)

    • Paused

    • Stopped

Activity state	Fragment callbacks triggered	Fragment lifecycle
Created	onAttach() onCreate() onCreateView() onActivityCreated()	Fragment is added and its layout is inflated
Started	onStart()	Fragment is active and visible
Resumed	onResume()	Fragment is active and ready for user interaction
Paused	onPause()	Fragment is paused because Activity is paused
Stopped	onStop()	Fragment is stopped and no longer visible
Destroyed	onDestroyView() onDestroy() onDetach()	Fragment is destroyed

@Override onCreate(Bundle savedInstanceState):

• System calls onCreate() when the Fragment is created

• Initialize Fragment components and variables (preserved if the Fragment is paused and resumed)

• Always include super.onCreate(savedInstanceState) in lifecycle callbacks

@Override onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState):

• Inflate XML layout—required if Fragment has a UI

• System calls this method to make Fragment visible

• Must return the root View of Fragment layout or null if the Fragment does not have a UI

More Callbacks
onAttach()	Called when Fragment is first attached to Activity
onPause()	Called when Activity is paused
onResume()	Called by Activity to resume a visible Fragment
onActivityCreated()	Called when Activity onCreate() method has returned
onDestroyView()	Called when View previously created by onCreateView() is detached from Fragment

onActivityCreated(): Called when the Activity onCreate() method has returned

• Called after onCreateView() and before onViewStateRestored()
• Retrieve views or restore state

• Use setRetainInstance() to keep Fragment instance when Activity is recreated

Use onDestroyView() to perform action after Fragment is no longer visible

• Called afteronStop() and before onDestroy()
• View that was created in onCreateView() is destroyed

• A new View is created next time Fragment needs to be displayed

Activity Context

When Fragment is active or resumed:

• Use getActivity() to get theActivity that started the fragment
• Find a View in the Activity layout:

View listView = getActivity().findViewById(R.id.list);

Get Fragment by calling findFragmentById() on FragmentManager:

ExampleFragment fragment = (ExampleFragment)
     getFragmentManager().findFragmentById(R.id.example_fragment);
// ...
mData = fragment.getSomeData();

Add Fragment to back stack: addToBackStack(null)

• Host Activity maintains back stack even after Fragment is removed

• Allows navigation with Back button

fragmentTransaction.add(R.id.fragment_container, fragment);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();