the docs on setRetainInstance say :
This can only be used with fragments not in the back stack.
so I started playing with it.
I have one Activity with adds first frag A
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.content, new PackageFragment());
ft.commit
then from this frag I run a method from parent Activity which adds frag B to backstack
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.content, new OrderFragment());
ft.addToBackStack(null);
ft.commit();
then I create log msg from onCreate,onDestroy,onSaveInstanceState,onActivityCreated...etc
I try two versions of this process. Rotating the device on each fragment.
Everything is as expected. onCreate, onDestroy on fragments fire
Everything is as expected?. onCreate, onDestroy on fragments dont fire
and all seems to work while fragments are in the backstack.. so why the docs say I shouldnt use it? What are the scenarios where I might get in trouble?
thanks
SetRetainInstance(true) allows the fragment sort of survive. Its members will be retained during configuration change like rotation. But it still may be killed when the activity is killed in the background.
You can use the getName() method of FragmentManager. BackStackEntry which was introduced in API level 14. This method will return a tag which was the one you used when you added the Fragment to the backstack with addTobackStack(tag) . Show activity on this post.
Use replace() to replace an existing fragment in a container with an instance of a new fragment class that you provide. Calling replace() is equivalent to calling remove() with a fragment in a container and adding a new fragment to that same container. transaction. commit();
Solution: Save required information as an instance variable in calling activity. Then pass that instance variable into your fragment.
Updated answer:
What are the scenarios where I might get in trouble?
When adding a Fragment
to the back stack and passing a Bundle
in the Fragment
from onSaveInstanceState()
to onCreateView()
on configuration change. Calling setRetainInstance(true)
will set the Bundle
to null on configuration change.
(I'm not sure a developer would actually attempt this since using setRetainInstance(true)
makes onSaveInstanceState()
kind of redundant, but I didn't see the behaviour documented in the API docs so I wrote up this answer).
If both addToBackStack()
and setRetainInstance(true)
are called, setRetainInstance()
partly alters the Fragment
lifecycle method calls and parameter values on configuration changes, compared to calling only addToBackStack()
.
Specifically, in the test below, looking a differences between calling only addToBackStack()
and calling setRetainInstance(true)
as well, and seeing what happens on configuration change:
Calling addToBackStack()
but not setRetainInstance(true)
;
onCreate()
and onDestroy()
are called.onSaveInstanceState()
is received as a parameter in onCreateView()
.Calling both addToBackStack()
and setRetainInstance(true)
:
onCreate()
and onDestroy()
are not called. This is metioned in the API docs.onSaveInstanceState()
is not received in onCreateView()
. The passed-in Bundle
is null. A test with logged method calls and parameters tested for null:
In the Activity
:
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
MyFragment fragment;
if (savedInstanceState != null) {
fragment = (MyFragment) getFragmentManager().findFragmentByTag("my_fragment_tag");
} else {
fragment = new MyFragment();
FragmentTransaction t = getFragmentManager().beginTransaction();
t.addToBackStack(null);//toggle this
t.add(android.R.id.content, fragment, "my_fragment_tag").commit();
}
}
In the Fragment
:
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
setRetainInstance(true);//toggle this
}
and
@Override
public void onSaveInstanceState(Bundle outState) {
outState.putString("test", "value");
super.onSaveInstanceState(outState);
}
Test 1: Fragment lifecycle when addToBackStack()
is called , and setRetainInstance(true)
is not called
[Device rotated from portrait to landscape]
Test 2 & 3: Fragment lifecycle calls with setRetainInstance(true)
called, addToBackStack()
called / not called (same result):
[Device rotated from portrait to landscape]
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With