FragmentOverlapTest

AFragment.java

public class AFragment extends Fragment {
    public static AFragment newInstance() {
        AFragment fragment = new AFragment();
        return fragment;
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_a, container, false);
        view.findViewById(R.id.btn).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                ((MainActivity)getActivity()).startToB();
            }
        });
        return view;
    }
}

BFragment.java

public class BFragment extends Fragment {
    public static BFragment newInstance() {
        BFragment fragment = new BFragment();
        return fragment;
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_b, container, false);
        return view;
    }
}

MainActivity.java

public class MainActivity extends AppCompatActivity {
    private AFragment mAFragment;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mAFragment = (AFragment) getSupportFragmentManager().findFragmentByTag("A");
        if (mAFragment == null) {
            mAFragment = AFragment.newInstance();

            getSupportFragmentManager().beginTransaction()
                    .add(R.id.fl, mAFragment, "A")
                    .addToBackStack("A")
                    .commit();
        }
    }

    public void startToB() {
        getSupportFragmentManager().beginTransaction()
                .add(R.id.fl, BFragment.newInstance(), "B")
                .hide(mAFragment)
                .addToBackStack("B")
                .commit();
    }
}