我试图用 ActivityUnitTestCase 扩展测试类编写单元测试案例在我的应用程序活动。我可以成功运行测试用例较早，但现在我总是得到异常，同时运行它们。虽然我是pretty熟悉如何使用 NullPointerException异常，我无法弄清楚，导致此问题。所以我张贴这一个我找不到任何类似的问题。

堆栈跟踪显示我有一个在我的code此行

 活动= startActivity（mIntent，NULL，NULL）; 

但 startActivity 方法应该接受我测试活动的实例。我不知道为什么它返回null。

下面是堆栈跟踪。

 显示java.lang.NullPointerException：尝试写入到字段'android.os.IBinder android.app.ActivityThread.mLastIntendedActivityToken对空对象引用在android.app.Activity.performCreate（Activity.java:6372）在android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1119）在android.support.test.runner.MonitoringInstrumentation.callActivityOnCreate(MonitoringInstrumentation.java:346)在android.test.ActivityUnitTestCase.startActivity（ActivityUnitTestCase.java:158）在com.abc.test.MainActivityTest.access $ 100（MainActivityTest.java:16）在com.abc.test.MainActivityTest $ 1.run（MainActivityTest.java:34）在android.app.Instrumentation $ SyncRunnable.run（Instrumentation.java:1891）在android.os.Handler.handleCallback（Handler.java:739）在android.os.Handler.dispatchMessage（Handler.java:95）在android.os.Looper.loop（Looper.java:145）在android.app.ActivityThread.main（ActivityThread.java:6117）在java.lang.reflect.Method.invoke（本机方法）在java.lang.reflect.Method.invoke（Method.java:372）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1399）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:1194）试运行失败：仪表运行失败，原因是显示java.lang.NullPointerException 

下面是测试类

 公共类MainActivityTest扩展ActivityUnitTestCase＆LT; MainActivity＆GT; {    私人意图mIntent;    私人MainActivity活动;    公共MainActivityTest（）{        超（MainActivity.class）;    }    @覆盖    保护无效设置（）抛出异常{        super.setUp（）;        //创建一个意图发动目标活动，因为它不会自动由Android仪表启动        mIntent =新意图（getInstrumentation（）的getContext（），MainActivity.class。）;        //测试启动活动隔离，在主线程，以避免断言错误。        getInstrumentation（）。runOnMainSync（新的Runnable（）{            @覆盖            公共无效的run（）{                活性= startActivity（mIntent，NULL，NULL）;            }        }）;    }    @覆盖    保护无效拆解（）抛出异常{        super.tearDown（）;    }    / **     *测试此测试夹具的preconditions。     * /    @SmallTest    公共无效测试preconditions（）{        assertNotNull（MainActivity是空，getActivity（））;    }    @MediumTest    公共无效testSecondActivityWasLaunchedWithIntent（）{        //获取意图下一个活动启动        最终意图launchIntent = getStartedActivityIntent（）;        //验证意图是不为空。        assertNotNull（意图为空，launchIntent）;        //验证LaunchActivity说完后        assertTrue（isFinishCalled（））;    }} 

解决方案

有一个很好的机会东西在你的应用程序类（即，x扩展应用程序）崩溃早期。如果这是你会看到这个错误的情况下....结帐您的logcat的痕迹。

I am trying to write Unit test cases for Activities in my app by extending the test class with ActivityUnitTestCase. I could successfully run the test cases earlier but now I'm always getting the exception while running them. Even though I'm pretty familiar with handling NullPointerExceptions, I couldn't figure out the problem that's causing this. I couldn't find any similar questions so I'm posting this one.

Stack trace shows me there is a null object reference at this line in my code

activity = startActivity(mIntent, null, null);

But the startActivity method is supposed to get the instance of the activity I'm testing. I'm not sure why it's returning null.

Here is the Stack trace.

java.lang.NullPointerException: Attempt to write to field 'android.os.IBinder android.app.ActivityThread.mLastIntendedActivityToken' on a null object reference
at android.app.Activity.performCreate(Activity.java:6372)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
at android.support.test.runner.MonitoringInstrumentation.callActivityOnCreate(MonitoringInstrumentation.java:346)
at android.test.ActivityUnitTestCase.startActivity(ActivityUnitTestCase.java:158)
at com.abc.test.MainActivityTest.access$100(MainActivityTest.java:16)
at com.abc.test.MainActivityTest$1.run(MainActivityTest.java:34)
at android.app.Instrumentation$SyncRunnable.run(Instrumentation.java:1891)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:6117)
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:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)

Test running failed: Instrumentation run failed due to 'java.lang.NullPointerException'

Here is the Test class

public class MainActivityTest extends ActivityUnitTestCase<MainActivity>{

    private Intent mIntent;
    private MainActivity activity;

    public MainActivityTest() {
        super(MainActivity.class);
    }

    @Override
    protected void setUp() throws Exception {
        super.setUp();
        //Create an intent to launch target Activity as it is not automatically started by Android Instrumentation
        mIntent = new Intent(getInstrumentation().getContext(), MainActivity.class);
        //Start the activity under test in isolation, in the main thread to avoid assertion error.
        getInstrumentation().runOnMainSync(new Runnable() {
            @Override
            public void run() {
                activity = startActivity(mIntent, null, null);
            }
        });
    }

    @Override
    protected void tearDown() throws Exception {
        super.tearDown();
    }

    /**
     * Tests the preconditions of this test fixture.
     */
    @SmallTest
    public void testPreconditions() {
        assertNotNull("MainActivity is null", getActivity());
    }

    @MediumTest
    public void testSecondActivityWasLaunchedWithIntent() {
        // Get the intent for the next started activity
        final Intent launchIntent = getStartedActivityIntent();
        //Verify the intent was not null.
        assertNotNull("Intent was null", launchIntent);
        //Verify that LaunchActivity was finished
        assertTrue(isFinishCalled());
    }
}

There's a good chance something in your application class (i.e. X extends Application) is crashing early on. If that's the case you'll see this error.... Checkout your logcat for traces.