Android Error [Attempt to invoke virtual method 'void android.app.ActionBar' on a null object reference]


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I have a code module which implements viewpager with navigation drawer, however, when I run the code I get the following error

01-26 09:20:02.958: D/AndroidRuntime(18779): Shutting down VM
01-26 09:20:02.959: E/AndroidRuntime(18779): FATAL EXCEPTION: main
01-26 09:20:02.959: E/AndroidRuntime(18779): Process: com.example.tabwithslidingdrawer, PID: 18779
01-26 09:20:02.959: E/AndroidRuntime(18779): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.tabwithslidingdrawer/com.example.tabwithslidingdrawer.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
01-26 09:20:02.959: E/AndroidRuntime(18779):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2314)
01-26 09:20:02.959: E/AndroidRuntime(18779):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2388)
01-26 09:20:02.959: E/AndroidRuntime(18779):    at android.app.ActivityThread.access$800(ActivityThread.java:148)
01-26 09:20:02.959: E/AndroidRuntime(18779):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1292)
01-26 09:20:02.959: E/AndroidRuntime(18779):    at android.os.Handler.dispatchMessage(Handler.java:102)
01-26 09:20:02.959: E/AndroidRuntime(18779):    at android.os.Looper.loop(Looper.java:135)
01-26 09:20:02.959: E/AndroidRuntime(18779):    at android.app.ActivityThread.main(ActivityThread.java:5312)
01-26 09:20:02.959: E/AndroidRuntime(18779):    at java.lang.reflect.Method.invoke(Native Method)
01-26 09:20:02.959: E/AndroidRuntime(18779):    at java.lang.reflect.Method.invoke(Method.java:372)
01-26 09:20:02.959: E/AndroidRuntime(18779):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
01-26 09:20:02.959: E/AndroidRuntime(18779):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
01-26 09:20:02.959: E/AndroidRuntime(18779): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
01-26 09:20:02.959: E/AndroidRuntime(18779):    at com.example.tabwithslidingdrawer.MainActivity.onCreate(MainActivity.java:95)
01-26 09:20:02.959: E/AndroidRuntime(18779):    at android.app.Activity.performCreate(Activity.java:5953)
01-26 09:20:02.959: E/AndroidRuntime(18779):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1128)
01-26 09:20:02.959: E/AndroidRuntime(18779):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2267)
01-26 09:20:02.959: E/AndroidRuntime(18779):    ... 10 more
09:20:02.959: E/AndroidRuntime(18779): Caused by:
java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null
object reference 01-26 09:20:02.959: E/AndroidRuntime(18779):     at
com.example.tabwithslidingdrawer.MainActivity.onCreate(MainActivity.java:95)

points to this line

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

entire code http://pastebin.com/u1K72fr7

My manifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.tabwithslidingdrawer"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="19" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/Theme.Tabwithpager" >
        <activity
            android:name="com.example.tabwithslidingdrawer.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

</manifest>

android:theme="@style/Theme.Tabwithpager"

code http://pastebin.com/EFQLzRej

================================================================== EDIT/UPDATE:

What I learnt from this

Whenever such an error occurs

1. Check what kind of Activity is being used, is it a simple android.app Activity or an AppCompatActivity or an ActionBarActivity and so on.

2. Check if your activity type which is extended falls under the compat category

example android.app based Activity/Fragment are non appCompat types, whereas android.support.v4.app.Fragment or android.support.v4.app.ActivityCompat are appCompat based

if it falls under appCompat we use getSupportActionBar() else for android.app types we can use getActionBar()

3. Check the theme applied to the activity in question in the manifest file

example: In the manifest file if theme applied is say android:theme="@android:style/Theme.Holo.Dialog" getActionBar() will work

but if theme applied for the activity in the manifest is as follows android:theme="@style/Theme.AppCompat.Light" then you have to use getSupportActionBar()



All Answers
  • Translate

    Your code is throwing on com.example.tabwithslidingdrawer.MainActivity.onCreate(MainActivity.java:95):

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

    The problem is pretty simple- your Activity is inheriting from the new android.support.v7.app.ActionBarActivity. You should be using a call to getSupportActionBar() instead of getActionBar().

    If you look above around line 65 of your code you'll see that you're already doing that:

            actionBar = getSupportActionBar();
            actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_LIST);
            // TODO: Remove the redundant calls to getSupportActionBar()
            //       and use variable actionBar instead
            getSupportActionBar().setDisplayHomeAsUpEnabled(true);
            getSupportActionBar().setHomeButtonEnabled(true);
    

    And then lower down around line 87 it looks like you figured out the same:

            getSupportActionBar().setTitle(
                            Html.fromHtml("<font color=\"black\">" + mTitle + " - "
                                            + menutitles[0] + "</font>"));
            // getActionBar().setTitle(mTitle +menutitles[0]);
    

    Notice how you commented out getActionBar().


  • Translate

    If anybody wants to use android.app.ActionBar and android.app.Activity you should change the app theme in styles.xml, for example:

    <style name="AppTheme" parent="android:Theme.Holo.Light.DarkActionBar">
    

    The problem is you could be using an AppCompat theme.

    On the other hand, if you want to use android.support.v7.app.ActionBar and you extend your activity with AppCompatActivity then you must use an AppCompat theme to avoid this issue, for example:

    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    

    Hope this helps.


  • Translate

    when you extend appcompatActivity then use

    this.getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    

    and when you extend ActionBar then use

    this.getActionBar().setDisplayHomeAsUpEnabled(true);
    

    dont forget to call this function in oncreate after initializing the toolbar/actionbar


  • Translate

    I think what you want to do is cast getActivity(). For example:

    ((AppCompatActivity)getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    This is what you need to do with the new support libraries. AppCompatActivity has replaced ActionBarActivity.


  • Translate

    Try to check here

    res >> values >> styles.xml

    make sure that there no code like this

    <item name="windowActionBar">false</item>
    

    if there are code like that, you can disable for a while, or erase it


  • Translate

    When use AppCompatActivity must call

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

    Before getSupportActionBar()

    public class PageActivity extends AppCompatActivity {
         @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_item);
            Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
            setSupportActionBar(toolbar);
            this.getSupportActionBar().setDisplayHomeAsUpEnabled(false);
    
        }
    }
    

  • Translate

    The Up Button is usually activated for Low-level Activities. In your manifest I only see the MainActivity. I don't think it makes sense to activate the up button for the main activity. Create an activity, then in the manifest add the parentActivityName attribute. Then activate the up button on the activity's onCreate method.
    This should help.
    https://developer.android.com/training/appbar/up-action.html


  • Translate

    In my case I had the same error but my mistake was that I didn't declare my Toolbar.

    So, before I use getSupportActionBar I had to find my toolbar and set the actionBar

        appbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(appbar);
    
        getSupportActionBar().setHomeAsUpIndicator(R.drawable.ic_nav_menu);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    

  • Translate

    For anyone else who has a BaseActivity, and a child that extends from it, make sure the super.onCreate() is called first before you do anything. The old Activity would work if you called super.onCreate() afterwards.

    Child extends Activity - could call super after you did stuff

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

    Child extends AppCompatActivity - ya gotta call super first

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState); //do this first
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    

  • Translate

    If you are using android.app.ActionBar and android.app.Activity you should change the app theme in application tag:

    < application

    android:theme="@android:style/Theme.Holo.Light" >


  • Translate

    in this line in your activity:

    super.onCreate(savedInstanceState);
    setContentView(R.layout.Activity_Main);
    

    use this:

    super.onCreate(savedInstanceState);
    setContentView(R.layout.*);
    

    * is your activity


  • Translate

    In my case is because of styles.xml set the wrong parent theme, i.e. NoActionBar theme of course getSupportActionbar() is null:

    <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
    

    Changed it to something else fixed it:

    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    

  • Translate

    For those still having this issue, my issue was resolved in the AndroidManifest.xml file. Where it says <activity android:name=".MainActivity" android:theme="@style/AppTheme.NoActionBar">, you need to remove NoActionBar, making it <activity android:name=".MainActivity" android:theme="@style/AppTheme">, because with NoActionBar set the app doesnt know whether or not it wants an action bar when you call one up inside of MainActivity.java


  • Translate

    I got the same error once, I created a template for a default toolbar( toolbar.xml) and then in another view I created a collapsable toolbar.

    I required to add the collapsable toolbar to a view that show some information of the user(like whatsapp), but the method findViewById was referencing the default toolbar(id toolbar), not the collapsable one( id toolbar as well) yes, I wrote the same id to both toolbar, so when I tried to access the activity the app crashed showing me the error.

    I fixed the error by changing the id of the collapsable toolbar to id:col_toolbar and the error gone away and my app worked perfectly


  • Translate

    I know that this question is something old. But this can help many who present this problem.

    To solve this problem, check if there is a point of nullity. Then apply the corresponding configuration:

    if(getSupportActionBar() != null){
     getSupportActionBar().setDisplayHomeAsUpEnabled(true);
     getSupportActionBar().setHomeButtonEnabled(true);
    }
    

  • Translate

    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();
            }
        };
    

  • Translate

    The best solution do this in your Oncreate method

     ActionBar actionBar = getSupportActionBar();
    
            if(actionBar != null){
                actionBar.setDisplayHomeAsUpEnabled(true);
            }
    
    

    followed by a new class

    @Override
        public boolean onOptionsItemSelected(MenuItem item) {
    
            int id = item.getItemId();
    
            if(id == android.R.id.home){
                onBackPressed();
                return true;
            }
    
            return super.onOptionsItemSelected(item);
        }
    
    

  • Translate

    Try doing this:

                    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
                    getSupportActionBar().setHomeButtonEnabled(true);
                    actionBar = getSupportActionBar();
                    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_LIST);
    

    Instead of this:

    actionBar = getSupportActionBar();
                    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_LIST);
    
                    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
                    getSupportActionBar().setHomeButtonEnabled(true);