我不确定，这个图书馆的内容是什么，但结果总是不一致（至少对我而言）。
我在 ActivityB 中有 ActivityA ， ActivityB ， FragmentB1 。我将不得不将ActivityA的String ID传递给ActivityB，FragmentB1。由于我将在ActivityB中有一些片段也需要这个ID，我想为什么不使用EventBus。因此，ActivityA成为发布者和ActivityB，FragmentB1成为订阅者。
定义事件的POJO
public class EventUid {
private final String Uid;
public EventUid(String uid) {
Uid = uid;
}
public String getUid() {
return Uid;
}
}
ActivityA的代码如下。选择Spinner项时会运行以下代码。
EventBus.getDefault().post(new EventUid(Uid));
ActivityB，FragmentB1的代码如下。首先，我在onStart（）注册活动。
@Override
public void onStart() {
super.onStart();
EventBus.getDefault().register(this);
}
然后我在onStop（）中取消注册事件。
@Override
public void onStop() {
EventBus.getDefault().unregister(this);
super.onStop();
}
在订阅Event之前，我在ActivityB和FragmentB1中定义了一个String。
private String ProductUid;
最后，我在ActivityB和FragmentB1中订阅了该事件，如下所示。
@Subscribe(threadMode = ThreadMode.MAIN)
public void onEventUid(EventUid event) {
ProductUid = event.getUid();
}
我不确定我可能在哪里出错，但ActivityB和FragmentB1总是返回NullPointerException。有人能用正确的方式指出我吗？
由于
编辑：添加LogCat。 PS：此问题的活动，片段名称（以便于理解而命名）将与LogCat不同。
--------- beginning of crash
06-10 12:44:20.342 3019-3019/blog.deshki.editor E/AndroidRuntime: FATAL EXCEPTION: main
Process: blog.deshki.editor, PID: 3019
java.lang.RuntimeException: Unable to start activity ComponentInfo{blog.deshki.editor/blog.deshki.editor.screens.media.MediaActivity}: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()
at com.google.firebase.database.DatabaseReference.child(Unknown Source)
at blog.deshki.editor.screens.media.MediaActivity.firebaseSettings(MediaActivity.java:291)
at blog.deshki.editor.screens.media.MediaActivity.onCreate_aroundBody0(MediaActivity.java:267)
at blog.deshki.editor.screens.media.MediaActivity$AjcClosure1.run(MediaActivity.java:1)
at org.aspectj.runtime.reflect.JoinPointImpl.proceed(JoinPointImpl.java:149)
at com.frogermcs.androiddevmetrics.aspect.ActivityLifecycleAnalyzer.executeWithTracingIfEnabled(ActivityLifecycleAnalyzer.java:88)
at com.frogermcs.androiddevmetrics.aspect.ActivityLifecycleAnalyzer.ajc$inlineAccessMethod$com_frogermcs_androiddevmetrics_aspect_ActivityLifecycleAnalyzer$com_frogermcs_androiddevmetrics_aspect_ActivityLifecycleAnalyzer$executeWithTracingIfEnabled(ActivityLifecycleAnalyzer.java:1)
at com.frogermcs.androiddevmetrics.aspect.ActivityLifecycleAnalyzer.logAndExecute(ActivityLifecycleAnalyzer.java:66)
at blog.deshki.editor.screens.media.MediaActivity.onCreate(MediaActivity.java:262)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
06-10 12:44:20.358 1279-2221/? E/SurfaceFlinger: ro.sf.lcd_density must be defined as a build property