android - Fragment onResume() & onPause() is not called on backstack

Question

I have multiple fragment inside an activity. On a button click I am starting a new fragment, adding it to backstack. I naturally expected the onPause() method of current Fragment and onResume() of new Fragment to be called. Well it is not happening.

LoginFragment.java

public class LoginFragment extends Fragment{
  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
      final View view  =   inflater.inflate(R.layout.login_fragment, container, false);
      final FragmentManager mFragmentmanager =  getFragmentManager();

      Button btnHome  = (Button)view.findViewById(R.id.home_btn);
      btnHome.setOnClickListener(new View.OnClickListener() {
        public void onClick(View view){
           HomeFragment fragment    = new HomeFragment();
           FragmentTransaction ft2   =  mFragmentmanager.beginTransaction();
           ft2.setCustomAnimations(R.anim.slide_right, R.anim.slide_out_left
                    , R.anim.slide_left, R.anim.slide_out_right);
           ft2.replace(R.id.middle_fragment, fragment);
           ft2.addToBackStack(""); 
           ft2.commit();    
         }
      });
  }

  @Override
  public void onResume() {
     Log.e("DEBUG", "onResume of LoginFragment");
     super.onResume();
  }

  @Override
  public void onPause() {
    Log.e("DEBUG", "OnPause of loginFragment");
    super.onPause();
  }
}

HomeFragment.java

public class HomeFragment extends Fragment{
  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
     final View view  =   inflater.inflate(R.layout.login_fragment, container, false);
  }

  @Override
  public void onResume() {
     Log.e("DEBUG", "onResume of HomeFragment");
     super.onResume();
  }

  @Override
  public void onPause() {
     Log.e("DEBUG", "OnPause of HomeFragment");
     super.onPause();
  }
}

What I expected, was,

1. When button is clicked, LoginFragment gets replaced with HomeFragment, onPause() of LoginFragment, and onResume() of HomeFragment gets called
2. When back is pressed, HomeFragment is poped out and LoginFragment is seen, and onPause() of HomeFragment and onResume() of LoginFragment gets called.

What I am getting is,

1. When button is clicked, HomeFragment is correctly replacing LoginFragment, onResume() of HomeFragment is called, but onPause() of LoginFragment is never called.
2. When back pressed, HomeFragment is correctly popping to reveal LoginFragment, onPause() of HomeFragment gets called, but onResume() of LoginFragment never gets called.

Is this the normal behaviour? Why is onResume() of LoginFragment not getting called when I press the back button.

Answer 1

The fragments onResume() or onPause() will be called only when the Activities onResume() or onPause() is called. They are tightly coupled to the Activity.

Read the Handling the Fragment Lifecycle section of this article.