Animate drawer icon into arrow on setDisplayHomeAsUpEnabled?

I'm using setDisplayHomeAsUpEnabled in order to show the arrow instead of the drawer "burger" icon but it's not getting animated or anything. Instead it shows the arrow drawable instantaneously.

Home screen: (Album 1)

When you tap a movie: (Album 2)

The thing is, the icon does the animation just fine when I slide the drawer, which makes me think that maybe I'm not supposed to use setDisplayHomeAsUpEnabled for this: (Album 3)

Album: http://imgur.com/a/LkXbh

Here's my drawer toggle code:

    Toolbar toolbar = (Toolbar) findViewById(R.id.my_awesome_toolbar);
    setSupportActionBar(toolbar);

    drawerAdapter = new DrawerAdapter(this, App.getNavItems(), getSupportFragmentManager());
    drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawerList = (ExpandableListView) findViewById(R.id.left_drawer);

    // Set onGroupClick and onChildClick
    drawerAdapter.setClickEvents(MainActivity.this, drawerLayout, drawerList);
    drawerList.setAdapter(drawerAdapter);

    ActionBarDrawerToggle toolbarDrawerToggle = new ActionBarDrawerToggle(
            this,                 
            drawerLayout,        
            toolbar,             
            R.string.drawer_open, 
            R.string.drawer_close 
    ) {

        public void onDrawerClosed(View view) {
            super.onDrawerClosed(view);
            invalidateOptionsMenu();
        }

        public void onDrawerOpened(View view) {
            super.onDrawerOpened(view);
            invalidateOptionsMenu();
        }
    };
    drawerLayout.setDrawerListener(toolbarDrawerToggle);
    toolbarDrawerToggle.syncState();

EDIT: I want the animation not when opening the drawer, that works already. I would like to manually trigger the animation when I load a specific fragment. I may not have explained myself correctly.

Solution

I haven't tested this, but you may be able to achieve this by animating a float between 0 (drawer closed) and 1 (drawer open) and then passing the value into ActionBarDrawerToggle.onDrawerSlide(View, float). I believe that's how the toggle determines what state the animated toggle should be in.

Something like this should work.

ValueAnimator anim = ValueAnimator.ofFloat(start, end);
anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
    @Override
    public void onAnimationUpdate(ValueAnimator valueAnimator) {
        float slideOffset = (Float) valueAnimator.getAnimatedValue();
        toolbarDrawerToggle.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();