“尝试从空对象引用上的字段'int android.content.pm.ApplicationInfo.targetSdkVersion'读取”异常

Question

在使用 Mockito 运行 Espresso 测试时，我目前遇到这个问题，即在主 Activity 启动后，"Attempt to read from the field 'int android.content.pm.ApplicationInfo.targetSdkVersion' on a null object reference" 异常随机出现。

这是主Activity的初始化部分：

private MainActivity subject;
SingleActivityFactory<MainActivity> activityFactory =
    new SingleActivityFactory<MainActivity>(MainActivity.class) {
        @Override
        protected MainActivity create(Intent intent) {
            subject = spy(getActivityClassToIntercept());
            return subject;
        }
    };

@Rule public ActivityTestRule<MainActivity> mainActivityRule =
    new ActivityTestRule<>(activityFactory, true, false);

@Before
public void init() {
    mainActivityRule.launchActivity(null);
}

这是个例外：

java.lang.NullPointerException: Attempt to read from field 'int 
android.content.pm.ApplicationInfo.targetSdkVersion' on a null object 
reference
at android.view.View.getLayoutDirection(View.java:10277)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:446)
at android.view.View.measure(View.java:23169)
at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:1059)
at android.view.View.measure(View.java:23169)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:141)
at android.view.View.measure(View.java:23169)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1535
Test running failed: Instrumentation run failed due to 'Process crashed.'

还有崩溃的logcat：

2018-11-06 15:34:50.391 3299-3299/com.application.android E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.application.android, PID: 3299
java.lang.NullPointerException: Attempt to read from field 'int android.content.pm.ApplicationInfo.targetSdkVersion' on a null object reference
    at android.view.View.getLayoutDirection(View.java:10277)
    at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:446)
    at android.view.View.measure(View.java:23169)
    at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:1059)
    at android.view.View.measure(View.java:23169)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6749)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)

这里的问题是这个问题并不一致 - 失败率约为 40%。有人对这个问题有任何见解吗？ 另外，我应该提到，如果在没有使用 Mockito 监视 Activity 的情况下启动了 Activity，则不会出现此问题。

更新：

通过在 View.java 类中引入更改解决了该问题：

@ResolvedLayoutDir
public int getLayoutDirection() {
    //added check if ApplicationInfo is not null
    if(getContext().getApplicationInfo() == null){
            View v = this;
            Log.i("View id: ", getContext().getString(v.getId()));
            Log.e("Main error", "Bug catched");
    }
    else {
        final int targetSdkVersion = getContext().getApplicationInfo().targetSdkVersion;
        if (targetSdkVersion < Build.VERSION_CODES.JELLY_BEAN_MR1) {
            mPrivateFlags2 |= PFLAG2_LAYOUT_DIRECTION_RESOLVED;
            return LAYOUT_DIRECTION_RESOLVED_DEFAULT;
        }
    }
    return ((mPrivateFlags2 & PFLAG2_LAYOUT_DIRECTION_RESOLVED_RTL) ==
            PFLAG2_LAYOUT_DIRECTION_RESOLVED_RTL) ? LAYOUT_DIRECTION_RTL : LAYOUT_DIRECTION_LTR;
}

不修改系统类是否可以达到类似的效果？

Answer 1

我认为您的问题与previous issue有关，

在使用getFragmentManager() 方法时会产生类似的行为，

解决办法是：

改用 getSupportFragmentManager() 并从 v4.app.Fragment 类扩展

Answer 2

很可能Context 没有正确设置...

android.view.View 中的方法实际上是这样的：

public int getLayoutDirection() {
    return mViewFlags & LAYOUT_DIRECTION_MASK;
}

没有什么可以使用targetSdkVersion，但只有一次：

case R.styleable.View_fadingEdge:
    if (context.getApplicationInfo().targetSdkVersion >= ICE_CREAM_SANDWICH) {
        break;
    }

太糟糕了，测试代码不完整——很可能ActivityTestRule 是错误的；没有<T>，new ActivityTestRule<> 看起来很奇怪，应该看起来很相似：

new ActivityTestRule<MainActivity>(getActivityFactory(), true, false);

mainActivityRule.launchActivity(null); 也显得毫无用处。

有关功能示例，请参阅 InterceptingActivitySampleTest.java。

刚刚又找到一个例子，和题中的例子差不多：

@RunWith(AndroidJUnit4.class)
public class MainActivityTest {

    MainActivity subject;

    SingleActivityFactory<MainActivity> activityFactory = new SingleActivityFactory<MainActivity>(MainActivity.class) {
        @Override
        protected MainActivity create(Intent intent) {
            subject = spy(getActivityClassToIntercept());
            return subject;
        }
    };

    @Rule
    public ActivityTestRule<MainActivity> testRule = new ActivityTestRule<>(activityFactory, true, true);

    @Test
    public void activity_isBeingSpied() {
        verify(subject).setContentView(R.layout.layout_main);
    }
}