MainActivity.java

        getSupportFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {

            ValueAnimator anim;

            @Override
            public void onBackStackChanged() {
                if (getSupportFragmentManager().getBackStackEntryCount() > 0) {
//                    getSupportActionBar().setDisplayHomeAsUpEnabled(true); // show back button

                    anim = ValueAnimator.ofFloat(0, 1);

                    toolbar.setNavigationOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {
                            onBackPressed();
                        }
                    });
                } else {
                    anim = ValueAnimator.ofFloat(1, 0);

                    //show hamburger
                    getSupportActionBar().setDisplayHomeAsUpEnabled(false);
                    actionBarDrawerToggle.syncState();
                    toolbar.setNavigationOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {
                            drawerLayout.openDrawer(GravityCompat.START);
                        }
                    });
                }

                anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                    @Override
                    public void onAnimationUpdate(ValueAnimator valueAnimator) {
                        float slideOffset = (Float) valueAnimator.getAnimatedValue();
                        actionBarDrawerToggle.onDrawerSlide(drawerLayout, slideOffset);
                    }
                });
                anim.setInterpolator(new DecelerateInterpolator());
// You can change this duration to more closely match that of the default animation.
                anim.setDuration(500);
                anim.start();
            }
        });