Android app crashes on start with null pointer exception

Question

I am new to android and java I tried to create a navigation drawer screen in android from the tutorials :

http://www.androidhive.info/2013/11/android-sliding-menu-using-navigation-drawer/

but I am getting exception as :

--------- beginning of crash
05-02 11:23:49.153    2738-2738/kanix.highrise.com.highrise E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: kanix.highrise.com.highrise, PID: 2738
    java.lang.RuntimeException: Unable to start activity ComponentInfo{kanix.highrise.com.highrise/kanix.highrise.com.highrise.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
            at kanix.highrise.com.highrise.MainActivity.onCreate(MainActivity.java:88)
            at android.app.Activity.performCreate(Activity.java:5937)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
05-02 11:23:49.390    2738-2751/kanix.highrise.com.highrise I/art﹕ Background partial concurrent mark sweep GC freed 360(66KB) AllocSpace objects, 0(0B) LOS objects, 52% free, 465KB/977KB, paused 1.273ms total 220.874ms
05-02 11:26:01.559    2791-2791/kanix.highrise.com.highrise D/AndroidRuntime﹕ Shutting down VM
05-02 11:26:01.715    2791-2791/kanix.highrise.com.highrise E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: kanix.highrise.com.highrise, PID: 2791
    java.lang.RuntimeException: Unable to start activity ComponentInfo{kanix.highrise.com.highrise/kanix.highrise.com.highrise.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
            at kanix.highrise.com.highrise.MainActivity.onCreate(MainActivity.java:88)
            at android.app.Activity.performCreate(Activity.java:5937)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
05-02 11:26:01.772    2791-2803/kanix.highrise.com.highrise I/art﹕ Background partial concurrent mark sweep GC freed 345(52KB) AllocSpace objects, 0(0B) LOS objects, 51% free, 479KB/991KB, paused 43.642ms total 205.582ms
05-02 11:27:33.452    2835-2835/kanix.highrise.com.highrise I/art﹕ Not late-enabling -Xcheck:jni (already on)
05-02 11:27:33.581    2835-2835/kanix.highrise.com.highrise D/AndroidRuntime﹕ Shutting down VM
05-02 11:27:33.581    2835-2835/kanix.highrise.com.highrise E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: kanix.highrise.com.highrise, PID: 2835
    java.lang.RuntimeException: Unable to start activity ComponentInfo{kanix.highrise.com.highrise/kanix.highrise.com.highrise.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
            at kanix.highrise.com.highrise.MainActivity.onCreate(MainActivity.java:88)
            at android.app.Activity.performCreate(Activity.java:5937)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
05-02 11:29:36.573    2917-2917/kanix.highrise.com.highrise D/AndroidRuntime﹕ Shutting down VM
05-02 11:29:36.573    2917-2917/kanix.highrise.com.highrise E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: kanix.highrise.com.highrise, PID: 2917
    java.lang.RuntimeException: Unable to start activity ComponentInfo{kanix.highrise.com.highrise/kanix.highrise.com.highrise.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
            at kanix.highrise.com.highrise.MainActivity.onCreate(MainActivity.java:88)
            at android.app.Activity.performCreate(Activity.java:5937)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
           

at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

I copied the code and I had some activities in my code working perfectly but now I tried to add navigation drawer activity to my app but it crashes on start. My menifest file is like this:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="kanix.highrise.com.highrise" >

    <application
        android:allowBackup="true"
        android:icon="@mipmap/icon"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".StartActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.VIEW" />
                <action android:name="com.example.intentdemo.LAUNCH" />

                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
        <activity
            android:name=".LoginActivity"
            android:icon="@mipmap/ic_launcher"
            android:label="loginactivity" >
            <intent-filter>
                <action android:name="android.intent.action.VIEW" />
                <action android:name="com.example.intentdemo.LAUNCH" />

                <category android:name="android.intent.category.DEFAULT" />

                <data android:scheme="http" />
            </intent-filter>
        </activity>
        <activity
            android:name=".Dashboard"
            android:label="@string/title_activity_dashboard" >
            <intent-filter>
                <action android:name="android.intent.action.VIEW" />
                <action android:name="com.example.intentdemo.LAUNCH" />

                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
        <activity
            android:name=".MainActivity"
            android:label="@string/title_activity_main" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>


        </activity>
    </application>

</manifest>

My main activity java class is like this:

package kanix.highrise.com.highrise;



import java.util.ArrayList;

import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.content.res.Configuration;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.widget.DrawerLayout;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;

import kanix.highrise.com.highrise.adapter.NavDrawerListAdapter;
import kanix.highrise.com.highrise.model.NavDrawerItem;

public class MainActivity extends Activity {
    private DrawerLayout mDrawerLayout;
    private ListView mDrawerList;
    private ActionBarDrawerToggle mDrawerToggle;

    // nav drawer title
    private CharSequence mDrawerTitle;

    // used to store app title
    private CharSequence mTitle;

    // slide menu items
    private String[] navMenuTitles;
    private TypedArray navMenuIcons;

    private ArrayList<NavDrawerItem> navDrawerItems;
    private NavDrawerListAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mTitle = mDrawerTitle = getTitle();

        // load slide menu items
        navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items);

        // nav drawer icons from resources
        navMenuIcons = getResources()
                .obtainTypedArray(R.array.nav_drawer_icons);

        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        mDrawerList = (ListView) findViewById(R.id.list_slidermenu);

        navDrawerItems = new ArrayList<NavDrawerItem>();

        // adding nav drawer items to array
        // Home
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[0], navMenuIcons.getResourceId(0, -1)));
        // Find People
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[1], navMenuIcons.getResourceId(1, -1)));
        // Photos
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[2], navMenuIcons.getResourceId(2, -1)));
        // Communities, Will add a counter here
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[3], navMenuIcons.getResourceId(3, -1), true, "22"));
        // Pages
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[4], navMenuIcons.getResourceId(4, -1)));
        // What's hot, We  will add a counter here
        navDrawerItems.add(new NavDrawerItem(navMenuTitles[5], navMenuIcons.getResourceId(5, -1), true, "50+"));


        // Recycle the typed array
        navMenuIcons.recycle();

        mDrawerList.setOnItemClickListener(new SlideMenuClickListener());

        // setting the nav drawer list adapter
        adapter = new NavDrawerListAdapter(getApplicationContext(),
                navDrawerItems);
        mDrawerList.setAdapter(adapter);

        // enabling action bar app icon and behaving it as toggle button
        getActionBar().setDisplayHomeAsUpEnabled(true);
        getActionBar().setHomeButtonEnabled(true);

        mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
                R.drawable.ic_drawer, //nav menu toggle icon
                R.string.app_name, // nav drawer open - description for accessibility
                R.string.app_name // nav drawer close - description for accessibility
        ) {
            public void onDrawerClosed(View view) {
                getActionBar().setTitle(mTitle);
                // calling onPrepareOptionsMenu() to show action bar icons
                invalidateOptionsMenu();
            }

            public void onDrawerOpened(View drawerView) {
                getActionBar().setTitle(mDrawerTitle);
                // calling onPrepareOptionsMenu() to hide action bar icons
                invalidateOptionsMenu();
            }
        };
        mDrawerLayout.setDrawerListener(mDrawerToggle);

        if (savedInstanceState == null) {
            // on first time display view for first nav item
            displayView(0);
        }
    }

    /**
     * Slide menu item click listener
     * */
    private class SlideMenuClickListener implements
            ListView.OnItemClickListener {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position,
                long id) {
            // display view for selected nav drawer item
            displayView(position);
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // toggle nav drawer on selecting action bar app icon/title
        if (mDrawerToggle.onOptionsItemSelected(item)) {
            return true;
        }
        // Handle action bar actions click
        switch (item.getItemId()) {
        case R.id.action_settings:
            return true;
        default:
            return super.onOptionsItemSelected(item);
        }
    }

    /* *
     * Called when invalidateOptionsMenu() is triggered
     */
    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        // if nav drawer is opened, hide the action items
        boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
        menu.findItem(R.id.action_settings).setVisible(!drawerOpen);
        return super.onPrepareOptionsMenu(menu);
    }

    /**
     * Diplaying fragment view for selected nav drawer list item
     * */
    private void displayView(int position) {
        // update the main content by replacing fragments
        Fragment fragment = null;
        switch (position) {
        case 0:
            fragment = new HomeFragment();
            break;
        case 1:
            fragment = new FindPeopleFragment();
            break;
        case 2:
            fragment = new PhotosFragment();
            break;
        case 3:
            fragment = new CommunityFragment();
            break;
        case 4:
            fragment = new PagesFragment();
            break;
        case 5:
            fragment = new WhatsHotFragment();
            break;

        default:
            break;
        }

        if (fragment != null) {
            FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.beginTransaction()
                    .replace(R.id.frame_container, fragment).commit();

            // update selected item and title, then close the drawer
            mDrawerList.setItemChecked(position, true);
            mDrawerList.setSelection(position);
            setTitle(navMenuTitles[position]);
            mDrawerLayout.closeDrawer(mDrawerList);
        } else {
            // error in creating fragment
            Log.e("MainActivity", "Error in creating fragment");
        }
    }

    @Override
    public void setTitle(CharSequence title) {
        mTitle = title;
        getActionBar().setTitle(mTitle);
    }

    /**
     * When using the ActionBarDrawerToggle, you must call it during
     * onPostCreate() and onConfigurationChanged()...
     */

    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        // Sync the toggle state after onRestoreInstanceState has occurred.
        mDrawerToggle.syncState();
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        // Pass any configuration change to the drawer toggls
        mDrawerToggle.onConfigurationChanged(newConfig);
    }

}

Answer 1

You probably need to use an Action bar theme for your activity. Check out the first part of this document . You can specify a theme for the activity in the manifest in both the application and activity sections. For instance:

        android:theme="@style/Theme.AppCompat.Light"

Answer 2

The major reason why app is crashing is you are using support Action bar toggle with Action Bar.

Try this convert your Activity to ActionBarActivity and use SupportActionBar in place of Action bar. ALso do not forget to use AppCompact theme with this in your style.xml .

Answer 3

Your code have error on Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference at kanix.highrise.com.highrise.MainActivity.onCreate(MainActivity.java:88)

Check this link for to fixed the bugs.