How to fix getActionBar method may produce java.lang.NullPointerException

Question

I am using a toolbar as my actionbar in an activity. I am trying to add the method getActionBar().setDisplayHomeAsUpEnabled(true); to the Activity.java file for Up navigation for older devices.

The method produces the following error message in Android Studio:

Method invocation may produce java.lang.NullPointerException

The Up navigation on the toolbar works fine on newer devices...now I'm trying to figure out how to make sure it will work for older devices. Please advise.

From build.gradle:

dependencies {
   compile "com.android.support:appcompat-v7:22.1.0"
}

From AndroidManifest.xml:

android:theme="@style/Theme.AppCompat.NoActionBar.FullScreen"

From styles.xml

<style name="Theme.AppCompat.NoActionBar.FullScreen" parent="AppTheme">
<item name="android:windowNoTitle">true</item>
<item name="windowActionBar">false</item>
<item name="android:windowFullscreen">true</item>

from Activity.java

public class CardViewActivity extends AppCompatActivity {

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

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

    if (toolbar != null) {
        // Up navigation to the parent activity for 4.0 and earlier
        getActionBar().setDisplayHomeAsUpEnabled(true);
        toolbar.setNavigationIcon(R.drawable.ic_action_previous_item);
        toolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                onBackPressed();
            }
        });
    }

}

Isn't your theme one that does not have an ActionBar? – juunas Apr 22 '15 at 01:25 — juunas, Apr 22 '15 at 01:25

score 128 · Accepted Answer · edited May 23 '17 at 12:02

128

Actually Android Studio isn't showing you an "error message", it's just a warning.

Some answers propose the use of an assertion, Dalvik runtime has assertion turned off by default, so you have to actually turn it on for it to actually do something. In this case (assertion is turned off), what you're essentially doing is just tricking Android Studio to not show you the warning. Also, I prefer not to use "assert" in production code.

In my opinion, what you should do is very simple.

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

Update: In case you're using the support library version of the Action Bar, you should replace getActionBar() with getSupportActionBar().

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

edited May 23 '17 at 12:02

Community

1
1

answered Mar 01 '16 at 09:50

Adam G

1,527
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12

2

While I originally used assert to "solve" the warning, I agree that your recommended code is better than the assert hack. Answer has been upvoted and accepted. Note that I am using AppCompatActivity as a class so I must use getSupportActionBar() in my solution rather than the getActionBar() that you show above. – AJW Mar 03 '16 at 02:02
4

Why android studio not giving the same warning for other methods like getSupportActionBar().setTitle() ? – Piyush Kukadiya May 05 '17 at 06:30
I'm using the getSupportActionBar() != null but I am still thrown a null pointer on my toolbar. Does anyone know what is going on? I have tried the assert line, which also just throws a null pointer!??! What is going oN!??!?!?! – ZooMagic Mar 01 '18 at 09:51
@ZooMagic There are different reasons why it might throw a NPE. I advice you to search for other questions that are similar to yours or post your code on a new question. You need to share your layout file, manifest and Activity code. – Adam G Mar 01 '18 at 18:57

Bogdan Zurac · Answer 2 · 2015-06-12T08:57:09.337

34

First off, you need to set the toolbar as the support ActionBar. Then if you're certain it's going to be there all the time, just assert it as != null. This will tell the compiler it won't be null, so the null check passes.

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

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

   assert getSupportActionBar() != null;
   getSupportActionBar().setDisplayHomeAsUpEnabled(true); // it's getSupportActionBar() if you're using AppCompatActivity, not getActionBar()
}

edited Jun 12 '15 at 08:57

answered Apr 22 '15 at 10:40

Bogdan Zurac

6,348
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Ok, looks good but the assert line generates a "Cannot resolve symbol 'getSupportActionBar'" error in Android Studio. Should it be "getSupportActionBar()" ? Please advise. – AJW Apr 23 '15 at 22:19
1

You can only access getSupportActionBar when extending AppCompatActivity or FragmentActivity – Sheychan Aug 05 '15 at 08:49

score 8 · Answer 3 · answered Apr 25 '15 at 05:53

8

Thank You Andrew for your answer. If you have a Nav Drawer or something else that uses getSupportActionBar() you need to add assert getSupportActionBar() != null;

Peace,

Example:

@Override
public void setTitle(CharSequence title) {
    mTitle = title;
    assert getSupportActionBar() != null;
    getSupportActionBar().setTitle(mTitle);
}

answered Apr 25 '15 at 05:53

Scott

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3

Is this valid for production, or only for testing? – gian1200 Apr 26 '15 at 01:22
gian1200 I am not sure. A good question. I was planning to release my app soon, so I will be doing research before I do the release... Thx. – Scott Apr 28 '15 at 00:05
My guess is that the compiler will change it to something like "if it is null, then throw an assertExeption"; not allowing you to handle the error. – gian1200 Apr 28 '15 at 00:15

score 4 · Answer 4 · answered Jul 10 '15 at 07:07

4

Try this :

private ActionBar getActionBar() {
    return ((AppCompatActivity) getActivity()).getSupportActionBar();
}

answered Jul 10 '15 at 07:07

Shubham A.

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score 3 · Answer 5 · answered Mar 30 '16 at 08:51

3

What I have done is override the getSupportActionBar() method in my base Activity and add a @NonNull annotation. This way, I only get one lint warning in the base activity about how I use @NonNull annotation for something that has a @Nullable annotation.

    @NonNull
    @Override
    public ActionBar getSupportActionBar() {
        // Small hack here so that Lint does not warn me in every single activity about null
        // action bar
        return super.getSupportActionBar();
    }

answered Mar 30 '16 at 08:51

Catalin Morosan

7,897
11
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thanks for your answer. I don't know about using lint. Can you comment on any advantage your answer has vs. Adam Ghani's answer up above? – AJW Apr 01 '16 at 02:14
With Adam's approach you have to write the if statement in all your activities. With my approach you just have to override the getSupportActionBar in the base activity and the rest of the code remains as before. – Catalin Morosan Apr 02 '16 at 05:32

score 3 · Answer 6 · answered Jun 09 '16 at 07:31

I created a generic class such as:

public final class Cast
{
    private Cast() {}

    /**
     * Helps to eliminate annoying NullPointerException lint warning.
     */
    @android.support.annotation.NonNull
    public static <T> T neverNull(T value)
    {
        return value;
    }
}

then I can use it for any call with NullPointerException warning for which I am sure that it will never happen, e.g.

final ActionBar actionBar = Cast.neverNull(getSupportActionBar());
actionBar.setDisplayHomeAsUpEnabled(true);
actionBar.setHomeButtonEnabled(true);

P.S. don't forget to add "com.android.support:support-annotations" to your gradle file.

score 2 · Answer 7 · edited Oct 17 '15 at 17:38

2

add assert getSupportActionBar() != null; before getSupportActionBar().setDisplayHomeAsUpEnabled(true);

edited Oct 17 '15 at 17:38

Nikos

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answered Oct 17 '15 at 06:52

Pankaj K Sharma

240
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12

score 0 · Answer 8 · edited Jun 15 '16 at 06:54

0

 if(actionBar != null) {
  actionBar.setHomeButtonEnabled(true);
  actionBar.setBackgroundDrawable(ContextCompat.getDrawable(mContext,
                                  R.drawable.action_bar_gradient));
 }

edited Jun 15 '16 at 06:54

ρяσѕρєя K

132,198
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213

answered Jun 15 '16 at 06:27

Krishna

1,556
13
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score 0 · Answer 9 · edited Jul 05 '16 at 06:42

0

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

Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
toolbar.setTitle("Title");
setSupportActionBar(toolbar);
ActionBar actionBar = getSupportActionBar();
actionBar.setHomeButtonEnabled(true);
actionBar.setHomeAsUpIndicator(R.drawable.ic_action_previous_item);
actionBar.setDisplayHomeAsUpEnabled(true);

edited Jul 05 '16 at 06:42

kirtan403

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answered Jun 15 '16 at 06:46

Surendran

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score 0 · Answer 10 · answered Apr 03 '18 at 19:32

Alternatively you could assert actionbar to not null.Add the assertion before calling your actionbar as follows

assert getSupportActionBar() != null;

Final snippet would therefore look as follows:

    setSupportActionBar((Toolbar) findViewById(R.id.toolbar));
    assert getSupportActionBar() != null;
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);

score 0 · Answer 11 · answered Jan 24 '19 at 00:25

Try this :

setSupportActionBar (toolbar);
if(getSupportActionBar () != null) {
assert getSupportActionBar () != null;
getSupportActionBar ().setDisplayHomeUpEnabled(true);
}

Note that setSupportActionBar(toolbar) should be before getSupportActionBar().

score 0 · Answer 12 · edited Feb 01 '19 at 11:43

0

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

Replace the MainActivity extends AppCompatActivity to public class MainActivity extends AppCompatActivity

edited Feb 01 '19 at 11:43

Robert

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answered Feb 01 '19 at 11:22

MEGHA DOBARIYA

1,622
9
7

score 0 · Answer 13 · answered Apr 15 '19 at 08:17

just check getSupportActionBar not equal to null

    setSupportActionBar(toolbar);

    if(getSupportActionBar() != null) {
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setTitle("Daily Shopping List");
    }

score 0 · Answer 14 · answered Apr 15 '19 at 08:58

0

If you are importing

android.app.ActionBar

you have to use getActionBar()

and if you are importing

android.support.v7.app.ActionBar

use getSupportActionBar()

answered Apr 15 '19 at 08:58

MN. Vala

129
1
6

How to fix getActionBar method may produce java.lang.NullPointerException

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