NullPointerException: with ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference

Question

I get this nullPointerException on runtime:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method \'void android.app.ActionB

Answer 1

Put assert getActionBar () != null; after mActionBar = getActionBar();

Answer 2

This problem might be caused by your theme. Check it again, and make sure that it parent with Theme.AppCompat.Light.DarkActionBar.

<style name="MyTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <item name="android:windowNoTitle">true</item>
    <item name="windowActionBar">true</item>
    ...
</style>

If your activity extends AppCompatActivity or ActionBarActivity, call getSupportActionBar().

Answer 3

This is clearly not the problem of OP, but other people may find it useful: for me the solution was to call setContentView(R.layout.activity_main) before the configuration of actionbar.

Answer 4

In my case, I forgot to init my Toolbar, so, before using getSupportActionBar, I had to do this:

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

    getSupportActionBar().setHomeAsUpIndicator(R.drawable.ic_nav_menu);
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);

Answer 5

You should try this one. I think it will work.

    Toolbar toolbar = findViewById(R.id.toolbar1);
    setSupportActionBar(toolbar);

    mDrawerLayout = findViewById(R.id.drawer_layout);
    mDrawerLayout = findViewById(R.id.drawer_layout);
    mDrawerLayout.setDrawerShadow(R.drawable.rectagle_with_black_outer,
            GravityCompat.START);
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    getSupportActionBar().setHomeButtonEnabled(true);

    mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
            toolbar, R.string.navigation_drawer_close,
            R.string.navigation_drawer_close) {
        public void onDrawerClosed(View view) {
            invalidateOptionsMenu();
        }

        public void onDrawerOpened(View drawerView) {
            invalidateOptionsMenu();
        }
    };

Answer 6

If you check this answer in 2019 like me , the problem is about your android manifest:

<application
android:theme="@style/Theme.AppCompat.Light.NoActionBar"/>

Check the documentation here:

https://developer.android.com/training/appbar/setting-up.html

You also take in mind the previous answer from TetianaDev:

Instead of:

public class MainActivity extends Activity {

use:

public class MainActivity extends AppCompatActivity {

and instead of:

getActionBar().setTitle(mTitles);

use:

getSupportActionBar().setTitle(mTitles);

This works for me.