Android - Switch ActionBar Back Button to Navigation Button

I am having the following problem:

I know how to set up a toolbar to show a back button icon instead of a burger button icon.

From this:

to this:

using: getSupportActionBar().setDisplayHomeAsUpEnabled(true);

Now, I want to do the reverse action, I want to go from back button icon to burger icon:

to here:

How can I do this?

Update:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setSupportActionBar(mToolbar);
    getSupportActionBar().setDisplayShowTitleEnabled(false);
}

private void enableViews(boolean enable) {
    if(enable) {
        // Enables back button icon
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    } else {
        // TODO: Enables burger icon
    }
}

If I assume you're using android.support.v4.widget.DrawerLayout in your layout, then this approach may work for you; I've only tested on API 21 but given it's mostly using the support libraries, it should work (famous last words) on lower or higher targets.

import android.support.v7.app.ActionBarDrawerToggle
import android.support.v4.widget.DrawerLayout

    ActionBarDrawerToggle mDrawerToggle;
    DrawerLayout drawerLayout;
    private boolean mToolBarNavigationListenerIsRegistered = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setSupportActionBar(mToolbar);
        getSupportActionBar().setDisplayShowTitleEnabled(false);
        // Get DrawerLayout ref from layout
        drawerLayout = (DrawerLayout)findViewById(R.id.drawer);
        // Initialize ActionBarDrawerToggle, which will control toggle of hamburger.
        // You set the values of R.string.open and R.string.close accordingly.
        // Also, you can implement drawer toggle listener if you want.
        mDrawerToggle = new ActionBarDrawerToggle (this, drawerLayout, mToolbar, R.string.open, R.string.close);
        // Setting the actionbarToggle to drawer layout
        drawerLayout.addDrawerListener(mDrawerToggle);
        // Calling sync state is necessary to show your hamburger icon...
        // or so I hear. Doesn't hurt including it even if you find it works
        // without it on your test device(s)
        mDrawerToggle.syncState();
    }

    /**
     * To be semantically or contextually correct, maybe change the name
     * and signature of this function to something like:
     *
     * private void showBackButton(boolean show)
     * Just a suggestion.
     */
     private void enableViews(boolean enable) {

        // To keep states of ActionBar and ActionBarDrawerToggle synchronized,
        // when you enable on one, you disable on the other.
        // And as you may notice, the order for this operation is disable first, then enable - VERY VERY IMPORTANT.
        if(enable) {
            //You may not want to open the drawer on swipe from the left in this case  
            drawerLayout.setDrawerLockMode(DrawerLayout.LOCK_MODE_LOCKED_CLOSED);
            // Remove hamburger
            mDrawerToggle.setDrawerIndicatorEnabled(false);
            // Show back button
            getSupportActionBar().setDisplayHomeAsUpEnabled(true);
            // when DrawerToggle is disabled i.e. setDrawerIndicatorEnabled(false), navigation icon
            // clicks are disabled i.e. the UP button will not work.
            // We need to add a listener, as in below, so DrawerToggle will forward
            // click events to this listener.
            if(!mToolBarNavigationListenerIsRegistered) {
                mDrawerToggle.setToolbarNavigationClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        // Doesn't have to be onBackPressed
                        onBackPressed();
                    }
                });

                mToolBarNavigationListenerIsRegistered = true;
            }

        } else {
            //You must regain the power of swipe for the drawer. 
            drawerLayout.setDrawerLockMode(DrawerLayout.LOCK_MODE_UNLOCKED);

            // Remove back button
            getSupportActionBar().setDisplayHomeAsUpEnabled(false);
            // Show hamburger 
            mDrawerToggle.setDrawerIndicatorEnabled(true);
            // Remove the/any drawer toggle listener
            mDrawerToggle.setToolbarNavigationClickListener(null);
            mToolBarNavigationListenerIsRegistered = false;
        }

        // So, one may think "Hmm why not simplify to:
        // .....
        // getSupportActionBar().setDisplayHomeAsUpEnabled(enable);
        // mDrawer.setDrawerIndicatorEnabled(!enable);
        // ......
        // To re-iterate, the order in which you enable and disable views IS important #dontSimplify.
    }

The solution uses ActionBarDrawerToggle.setDrawerIndicatorEnabled to toggle the visibility of the hamburger icon and ActionBar.setDisplayHomeAsUpEnabled for visibility of the Up button, essentially making use of their respective drawable resources.

Other assumptions

• Your Activity theme extends Theme.AppCompat.Light.NoActionBar.

The top solutions did not work in this case:

• One Activity and multiple Fragments
• One Fragment (SettingsFragment) should show the back icon instead of the burger menu
• Using com.google.android.material.appbar.AppBarLayout, androidx.appcompat.widget.Toolbar and ActionBarDrawerToggle

I call this method in my Activity's onCreate():

private fun initBackStackChangeListener() {
    supportFragmentManager.addOnBackStackChangedListener {
        val fragment = supportFragmentManager.findFragmentById(R.id.fragment_container)

        if (fragment is SettingsFragment) {
            menuDrawerToggle?.isDrawerIndicatorEnabled = false
            drawer_layout.setDrawerLockMode(DrawerLayout.LOCK_MODE_LOCKED_CLOSED)
            menuDrawerToggle?.setToolbarNavigationClickListener { onBackPressed() }
            supportActionBar?.setDisplayHomeAsUpEnabled(true)
        } else {
            supportActionBar?.setDisplayHomeAsUpEnabled(false)
            drawer_layout.setDrawerLockMode(DrawerLayout.LOCK_MODE_UNLOCKED)
            menuDrawerToggle?.isDrawerIndicatorEnabled = true
            menuDrawerToggle?.toolbarNavigationClickListener = null
            menuDrawerToggle?.syncState()
        }
    }
}

And menuDrawerToggle is this:

menuDrawerToggle = ActionBarDrawerToggle(
        this, drawer_layout, toolbar,
        R.string.navigation_drawer_open,
        R.string.navigation_drawer_close
    ).apply {
        drawer_layout.addDrawerListener(this)
        this.syncState()
    }

Works like a charm. Maybe it helps anybody.

I found flexible solutions in The Google I/O 2017 Android App.

public Toolbar getToolbar() {
    if (mToolbar == null) {
        mToolbar = (Toolbar) findViewById(R.id.toolbar);
        if (mToolbar != null) {
            setSupportActionBar(mToolbar);
            mToolbar.setNavigationContentDescription(R.string.navdrawer_description_a11y);
            mToolbarTitle = (TextView) mToolbar.findViewById(R.id.toolbar_title);
            if (mToolbarTitle != null) {
                int titleId = getNavigationTitleId();
                if (titleId != 0) {
                    mToolbarTitle.setText(titleId);
                }
            }

            // We use our own toolbar title, so hide the default one
            getSupportActionBar().setDisplayShowTitleEnabled(false);
        }
    }
    return mToolbar;
}

/**
 * @param clickListener The {@link android.view.View.OnClickListener} for the navigation icon of
 *                      the toolbar.
 */
protected void setToolbarAsUp(View.OnClickListener clickListener) {
    // Initialise the toolbar
    getToolbar();
    if (mToolbar != null) {
        mToolbar.setNavigationIcon(R.drawable.ic_up);
        mToolbar.setNavigationContentDescription(R.string.close_and_go_back);
        mToolbar.setNavigationOnClickListener(clickListener);
    }
}

So the usage is really simple.

setToolbarAsUp(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        // onBackPressed();
        // or navigate to parent or some other intent
    }
});