The Fragment.setRetainInstance() method control whether a fragment instance is retained across Activity re-creation (such as from a configuration change). This can only be used with fragments not in the back stack. If set, the fragment lifecycle will be slightly different when an activity is recreated:
- onDestroy() will not be called (but onDetach() still will be, because the fragment is being detached from its current activity).
- onCreate(Bundle) will not be called since the fragment is not being re-created.
- onAttach(Activity) and onActivityCreated(Bundle) will still be called.
Refer to the last exercise, "UI elements lost after Activity/Fragment re-created". Consider the image_c, it is loaded in onCreateView(), only if savedInstanceState == null. Without setRetainInstance(true), it will not be loaded after orientation changed, because savedInstanceState != null.
MYTAG LogCat listed here:
Orientation changed:
- MainActivity.onPause
- MyFragment1.onPause
- MainActivity.onStop
- MyFragment1.onStop
- MainActivity.onDestroy
- MyFragment1.onDestroyView
- MyFragment1.onDestroy
- MyFragment1.onDetach
- MainActivity.onCreate / savedInstanceState != null
- MyFragment1.onAttach
- MyFragment1.onCreate / savedInstanceState != null
- MainActivity.onStart
- MyFragment1.onCreateView / savedInstanceState != null
- MyFragment1.onActivityCreated / savedInstanceState != null
- MyFragment1.onStart
- MainActivity.onResume
- MyFragment1.onResume
To know how setRetainInstance(true) affect lifecycle of Fragment, modify MyFragment.java from last exercise "UI elements lost after Activity/Fragment re-created", override onActivityCreated() method to call setRetainInstance(true).
@Override
public void onActivityCreated(Bundle savedInstanceState) {
recLifeCycle_with_savedInstanceState(savedInstanceState);
super.onActivityCreated(savedInstanceState);
setRetainInstance(true);
}
LogCat in Orientation Changed:
- MainActivity.onPause
- MyFragment1.onPause
- MainActivity.onStop
- MyFragment1.onStop
- MainActivity.onDestroy
- MyFragment1.onDestroyView
- MyFragment1.onDetach
- MainActivity.onCreate / savedInstanceState != null
- MyFragment1.onAttach
- MainActivity.onStart
- MyFragment1.onCreateView / savedInstanceState == null
- MyFragment1.onActivityCreated / savedInstanceState == null
- MyFragment1.onStart
- MainActivity.onResume
- MyFragment1.onResume
Download the files.
* the original chart of fragment lifecycle is taken here.
5 comments:
thanks
very well presented.
I found it useful and informative, thanks for the effort building the Figures.
"This can only be used with fragments not in the back stack."
Could you give us an example to support your statement? As I know we can use setRetainInstance() with fragments in the back stack.
Very nice post. Simple and straight to the point. You know what? A picture is worth a thousand words. Thanks!
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