Switching between Android Navigation Drawer image and Up caret when using fragments

Question

It's easy as 1-2-3.

If you want to achieve:

1) Drawer Indicator - when no fragments are in the Back Stack or the Drawer is opened

2) Arrow - when some Fragments are in the Back Stack

private FragmentManager.OnBackStackChangedListener
        mOnBackStackChangedListener = new FragmentManager.OnBackStackChangedListener() {
    @Override
    public void onBackStackChanged() {
        syncActionBarArrowState();
    }
};

@Override
protected void onCreate(Bundle savedInstanceState) {
    getSupportActionBar().setDisplayShowHomeEnabled(true);
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    mDrawerToggle = new ActionBarDrawerToggle(
            this,             
            mDrawerLayout,  
            R.drawable.ic_navigation_drawer, 
            0, 
            0  
    ) {

        public void onDrawerClosed(View view) {
            syncActionBarArrowState();
        }

        public void onDrawerOpened(View drawerView) {
            mDrawerToggle.setDrawerIndicatorEnabled(true);
        }
    };

    mDrawerLayout.setDrawerListener(mDrawerToggle);
    getSupportFragmentManager().addOnBackStackChangedListener(mOnBackStackChangedListener);
}

@Override
protected void onDestroy() {
    getSupportFragmentManager().removeOnBackStackChangedListener(mOnBackStackChangedListener);
    super.onDestroy();
}

private void syncActionBarArrowState() {
    int backStackEntryCount = 
        getSupportFragmentManager().getBackStackEntryCount();
    mDrawerToggle.setDrawerIndicatorEnabled(backStackEntryCount == 0);
}

3) Both indicators to act according to their shape

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    if (mDrawerToggle.isDrawerIndicatorEnabled() && 
        mDrawerToggle.onOptionsItemSelected(item)) {
        return true;
    } else if (item.getItemId() == android.R.id.home && 
               getSupportFragmentManager().popBackStackImmediate()) {
        return true;
    } else {
        return super.onOptionsItemSelected(item);
    }
}

P.S. See Creating a Navigation Drawer on Android Developers on other tips about the 3-lines indicator behavior.

You have written that, to implement lower-level fragments, you are replacing the existing fragment, as opposed to implementing the lower-level fragment in a new activity.

I would think that you would then have to implement the back functionality manually: when the user pressed back you have code that pops the stack (e.g. in Activity::onBackPressed override). So, wherever you do that, you can reverse the setDrawerIndicatorEnabled.

I've used next thing:

getSupportFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
            @Override
            public void onBackStackChanged() {
                if(getSupportFragmentManager().getBackStackEntryCount() > 0){
                    mDrawerToggle.setDrawerIndicatorEnabled(false);
                    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
                }
                else {
                    getSupportActionBar().setDisplayHomeAsUpEnabled(false);
                    mDrawerToggle.setDrawerIndicatorEnabled(true);
                }
            }
        });

If your up action bar button doesn't work, don't forget to add the listener :

// Navigation back icon listener
mDrawerToggle.setToolbarNavigationClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            onBackPressed();
        }
});

I've got some trouble implementing a drawer navigation with a home button, everything worked except the action buton.

Try handling the Home item selection in the MainActivity depending on the state of the DrawerToggle. This way you don't have to add same code to every fragment.

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Only handle with DrawerToggle if the drawer indicator is enabled.
    if (mDrawerToggle.isDrawerIndicatorEnabled() &&
            mDrawerToggle.onOptionsItemSelected(item)) {
        return true;
    }
    // Handle action buttons
    switch (item.getItemId()) {
        // Handle home button in non-drawer mode
        case android.R.id.home:
            onBackPressed();
            return true;

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

FOLLOW UP

The solution given by @dzeikei is neat, but it can be extended, when using fragments, to automatically handle setting back the drawer indicator when the backstack is empty.

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Only handle with DrawerToggle if the drawer indicator is enabled.
    if (mDrawerToggle.isDrawerIndicatorEnabled() &&
            mDrawerToggle.onOptionsItemSelected(item)) {
        return true;
    }
    // Handle action buttons
    switch (item.getItemId()) {
        // Handle home button in non-drawer mode
        case android.R.id.home:
            // Use getSupportFragmentManager() to support older devices
            FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.popBackStack();
            // Make sure transactions are finished before reading backstack count
            fragmentManager.executePendingTransactions();
            if (fragmentManager.getBackStackEntryCount() < 1){
                mDrawerToggle.setDrawerIndicatorEnabled(true);  
            }
            return true;

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

EDIT

For the question of @JJD.

The fragments are held/managed in an activity. The above code is written once in that activity, but only handle the up caret for the onOptionsItemSelected.

In one of my apps I also needed to handle the behavior of the up caret when the back button was pressed. This can be handle by overriding onBackPressed.

@Override
public void onBackPressed() {
    // Use getSupportFragmentManager() to support older devices
    FragmentManager fragmentManager = getFragmentManager();
    fragmentManager.executePendingTransactions();
    if (fragmentManager.getBackStackEntryCount() < 1){
        super.onBackPressed();
    } else {
        fragmentManager.executePendingTransactions();
        fragmentManager.popBackStack();
        fragmentManager.executePendingTransactions();
        if (fragmentManager.getBackStackEntryCount() < 1){
            mDrawerToggle.setDrawerIndicatorEnabled(true);
        }
    }
};

Note the code duplication between onOptionsItemSelected and onBackPressed which can be avoided by creating a method and calling that method in both places.

Also note I add two more times executePendingTransactions which in my case was required or else I had sometimes strange behaviors of the up caret.