How fragment is restoring its view state?

Question

I am trying to explore about how fragments are managed by android framework and through my research I got to know so many new things that I didn't know about fragments but I got stuck at one point and can't figure out how this is happening.

Please try to understand my scenario first. It goes like that: I have one Activity which add two fragments one by one. When activity is first loaded then Fragment A is attached to it using below code:

private void initFirstFragment(){
    Bundle bundle = new Bundle();
    bundle.putString("TEXT_TO_SHOW", "FIRST ACTIVITY\nFIRST DUMMY FRAGMENT");
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.replace(R.id.frameLayoutFragmentContainer, FirstDummyFragment.newInstance(bundle), FirstDummyFragment.class.getSimpleName());
    fragmentTransaction.addToBackStack(null);
    fragmentTransaction.commit();
}

These callback methods of Fragment A is called when it is loaded

FirstDummyFragment: onCreate: savedInstanceState--->null

FirstDummyFragment: onCreateView: savedInstanceState--->null

FirstDummyFragment: onResume

Now in Fragment A, I have a edit text and I type some text into it.

When a button is clicked inside an Activity then Fragment B is added to same container using below code:

public void openSecondFragment() {
    Bundle bundle = new Bundle();
    bundle.putString("TEXT_TO_SHOW", "FIRST ACTIVITY\nSECOND DUMMY FRAGMENT");
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.replace(R.id.frameLayoutFragmentContainer, SecondDummyFragment.newInstance(bundle), SecondDummyFragment.class.getSimpleName());
    fragmentTransaction.addToBackStack(null);
    fragmentTransaction.commit();
}

Below callback methods are called after adding Fragment B

SecondDummyFragment: onCreate: savedInstanceState--->null

FirstDummyFragment: onDestroyView

SecondDummyFragment: onCreateView

SecondDummyFragment: onResume

When I press back button, Fragment B is destroyed and Fragment A comes to foreground and below callback methods are called

SecondDummyFragment: onDestroyView

SecondDummyFragment: onDestroy

SecondDummyFragment: onDetach

FirstDummyFragment: onCreateView: savedInstanceState--->null

FirstDummyFragment: onResume

And the edit text of fragment A contains same text that I entered into it earlier before adding Fragment B. I am confused how android is restoring Fragment A's view state even if savedInstanceState is null and onCreateView returns a whole new View object when Fragment A is created again.

Answer 1

Finally I found my answer here .

Android is designed this way. View State Saving/Restoring are internally called inside Fragment in this case. As a result, every single View that is implemented a View State Saving/Restoring internally, for example EditText or TextView with android:freezeText="true", will be automatically saved and restored the state. Causes it to display just perfectly the same as previous.