FragmentManager.put/getFragment vs findFragmentByTag

Issue

More to the point, in onCreate/onCreateView I am already calling FragmentManager.findFragmentByTag() to lookup any existing instance of my fragment, and it seems to find it.

So what is the point of putFragment/getFragment? Does it save something extra or cause additional lifecycle stuff to happen? Is it just an alternative to findFragmentByTag() that does more or less the same thing? Because it seems to me that the fragment is being automatically saved for me without needing to use FragmentManager.putFragment().

Solution

So what is the point of putFragment/getFragment?

According to the current implementation, what putFragment(Bundle bundle, String key, Fragment fragment) do is put the index of a fragment into the bundle with the parameter key. And then getFragment(Bundle bundle, String key) get the fragment at the same index which can be retrieved from the bundle with the same key. A Fragment has its index in the FragmentManager only after it is added to it, so putFragment() can be called on a Fragment only after it is added.

Does it save something extra or cause additional lifecycle stuff to happen?

It save the index of a Fragment only, no more things else, nor do it cause any additional lifecycle stuff.

Is it just an alternative to findFragmentByTag() that does more or less the same thing?

Yes, I thik so.

According to the current implementation, what putFragment/getFragment does can be achieved with findFragmentByTag() too. But the function of putFragment/getFragment are quite limited because you can't use them without the bundle parameter, means you must call putFragment() in onSaveInstanceState().

Answered By - Lei Guo