getActionBar() works fine on devices/simulator but returns null in testcases

问题

Application supports minSdk=14 and have ActionBar on every Activity.

Application works fine since a long time and shows ActionBar on every Activity. Now I am writing Android JUnit Testcases but it gives NullPointException on line

  getActionBar().setDisplayHomeAsUpEnabled(true);

The bottom line is getActionBar() works on devices but returns null during test cases. If I remove the line then testcases are fine.

Here's how activity looks like.

protected void onCreate(Bundle savedInstanceState) {      
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_order);
      getActionBar().setDisplayHomeAsUpEnabled(true);

// other stuff under it

 }

JUnits are simple Android JUnit Testcases without any framework.

public class OrderActivityTest extends ActivityUnitTestCase<OrderActivity> {   

  private OrderActivity activity;

  public OrderActivityTest() {        
          super(OrderActivity.class);   
    }   

    protected void setUp() throws Exception {
         super.setUp();
         Intent intent = new Intent(getInstrumentation().getTargetContext(),OrderActivity.class);
         startActivity(intent, null, null);
         activity = getActivity();
    }

  public void testPreConditions() {
         assertTrue(activity != null);    
     }  
 }

And finally here's the exception while running test case.

java.lang.NullPointerException
at com.example.name.OrderActivity.onCreate(OrderActivity.java:176)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.test.ActivityUnitTestCase.startActivity(ActivityUnitTestCase.java:158)
at com.example.name.test.OrderActivityTest.setUp(OrderActivityTest.java:23)
at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:191)
at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:176)
at android.test.InstrumentationTestRunner.onStart(InstrumentationTestRunner.java:554)
at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1701)

Line 176 is getActionBar().setDisplayHomeAsUpEnabled(true);

回答1:

getActionBar() is probably returning null here. The title needs to be visible, make sure you don't have things like this there:

android:theme="@android:style/Theme.Black.NoTitleBar

This would cause an error in getActionBar() being null.

来源：https://stackoverflow.com/questions/23189694/getactionbar-works-fine-on-devices-simulator-but-returns-null-in-testcases