Navigation DrawerLayout button never changes to back button and won't navigate

Question

I am using a DrawerLayout with and adding a new Fragment each time the user taps an item from the drawer menu. This works perfectly.

Within one of those fragments the user can navigate to another fragment:

private void loadArchives() {

    PUCNewsArchive news_archive = new PUCNewsArchive();

    getFragmentManager()
    .beginTransaction()
    .add(R.id.container_frame, news_archive, "news_archives")
    .addToBackStack(null)
    .commit();

}

This will correctly add another fragment to the stack. BUT, it does not change the action bar drawer button/icon to a back button. So, in tapping that just opens the drawer again, which is should not do. The only way to navigate back is the use the hardware back button which does go back to the previous fragment. I tried adding the following to my main Activity to see what was going on:

@Override
public void onBackPressed(){
    FragmentManager fm = getFragmentManager();
    if (fm.getBackStackEntryCount() > 0) {
        Log.i("MainActivity", "popping backstack");
        fm.popBackStack();
    } else {
        Log.i("MainActivity", "nothing on backstack, calling super");
        super.onBackPressed();
    }
}

But that is only ever called when I use the hardware back button, as the drawer button is only ever opening the drawer.

I assume this should be checking to see if it should open the drawer or navigate:

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    if (mDrawerToggle.onOptionsItemSelected(item)) {
        return true;
    }

    switch(item.getItemId()) {
    case android.R.id.home:

        return true;
    default:
        return super.onOptionsItemSelected(item);
    }

}

What have I missed? Why is the drawer button never changing to a back button nor acting like one?

Answer 1

You don't need to use the onBackPressed().

I had a very similar situation in my app. Here is how I got it to work:

I created a method in the main activity:

public void foo(int fragment_id) {
        if(fragment_id == some_id){
            // keep the drawer carat
            mDrawerToggle.setDrawerIndicatorEnabled(true);
        }else{
            // Disable the  drawer carat, and enable the back button
            mDrawerToggle.setDrawerIndicatorEnabled(false);
            getActionBar().setDisplayHomeAsUpEnabled(true);
        }
    }

I call this method from onResume() of each fragment, and pass it that particular fragments id. Alternatively, you can call it from the loadFragment()/loadArchives() method in your main activity. This works fine for me.