RxJava线程切换

Question

RxBottomNavigationView.itemSelections(sections).map(menuItem -> menuItem.getTitle().toString()) 
      .observeOn(AndroidSchedulers.mainThread()).map(this::insertCategoryHeadersForSection) 
      .subscribeOn(Schedulers.computation()).observeOn(AndroidSchedulers.mainThread()) 
      .compose(bindToLifecycle()).subscribe(itemInfos -> dishRecyclerAdapter.animateTo(itemInfos)); 

上面的代码抛出此异常：

java.lang.IllegalStateException: Fatal Exception thrown on Scheduler. 
at io.reactivex.android.schedulers.HandlerScheduler$ScheduledRunnable.run(HandlerScheduler.java:111) 
at android.os.Handler.handleCallback(Handler.java:739) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5417) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'boolean io.reactivex.internal.fuseable.SimpleQueue.isEmpty()' on a null object reference 
at io.reactivex.internal.operators.observable.ObservableObserveOn$ObserveOnObserver.drainNormal(ObservableObserveOn.java:172) 
at io.reactivex.internal.operators.observable.ObservableObserveOn$ObserveOnObserver.run(ObservableObserveOn.java:252) 
at io.reactivex.android.schedulers.HandlerScheduler$ScheduledRunnable.run(HandlerScheduler.java:109) 
at android.os.Handler.handleCallback(Handler.java:739)  
at android.os.Handler.dispatchMessage(Handler.java:95)  
at android.os.Looper.loop(Looper.java:148)  
at android.app.ActivityThread.main(ActivityThread.java:5417)  
at java.lang.reflect.Method.invoke(Native Method) 

我试图从BottomNavigationView得到itemSelections事件，那么该项目映射到它的标题（主线程），然后在后台线程上运行长操作，然后再次在主线程上接收该操作的输出。请帮助。提前致谢。

Answer 1

您已遇到bug in RxBinding2固定在回购协议中但尚未发布。其原因是通过使用subscribeOn(Schedulers.computation())，您不会将计算移动到后台，但会使RxBottomNavigationView.itemSelections(sections)发生在被禁止的后台线程上并导致您的流（和应用程序）崩溃。

你应该这样做，而不是：

RxBottomNavigationView.itemSelections(sections) 
.subscribeOn(AndroidSchedulers.mainThread())  // <------------------------ 
.map(menuItem -> menuItem.getTitle().toString()) // main thread 
.observeOn(Schedulers.computation())    // <------------------------ 
.map(this::insertCategoryHeadersForSection)  // background 
.observeOn(AndroidSchedulers.mainThread())  // <------------------------ 
.compose(bindToLifecycle()) 
.subscribe(itemInfos ->       // main 
    dishRecyclerAdapter.animateTo(itemInfos));