关于 Retrofit 2.0 Fatal Exception thrown on Scheduler.Worker thread.
异常是在网络未连接的情况：
第一次进来Activity点击请求是不会报错的只会在onError方法中返回
java.net.ConnectException
而第二次进来Activity点击请求是不会报错的只会在onError方法中也是返回
java.net.ConnectException
看上去似乎没什么问题，但是你按返回键退出程序再次进来点击请求的时候就会出现
08-12 08:34:47.332 30801-30801/com.xxz.android E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.xxz.android, PID: 30801
java.lang.IllegalStateException: Fatal Exception thrown on Scheduler.Worker thread.
at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:62)
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$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: rx.exceptions.OnErrorFailedException: Error occurred when trying to propagate error to Observer.onError
at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:192)
at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:120)
at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.checkTerminated(OperatorObserveOn.java:264)
at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.call(OperatorObserveOn.java:207)
at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55)
at android.os.Handler.handleCallback(Handler.java:739)?
at android.os.Handler.dispatchMessage(Handler.java:95)?
at android.os.Looper.loop(Looper.java:148)?
at android.app.ActivityThread.main(ActivityThread.java:5417)?
at java.lang.reflect.Method.invoke(Native Method)?
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)?
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)?
Caused by: rx.exceptions.CompositeException: 2 exceptions occurred.
at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:192)?
at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:120)?
at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.checkTerminated(OperatorObserveOn.java:264)?
at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.call(OperatorObserveOn.java:207)?
at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55)?
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$MethodAndArgsCaller.run(ZygoteInit.java:726)?
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)?
Caused by: rx.exceptions.CompositeException$CompositeExceptionCausalChain: Chain of Causes for CompositeException In Order Received =>
at android.util.Log.getStackTraceString(Log.java:338)
at com.android.internal.os.RuntimeInit.Clog_e(RuntimeInit.java:61)
at com.android.internal.os.RuntimeInit.-wrap0(RuntimeInit.java)
at com.android.internal.os.RuntimeInit$UncaughtHandler.uncaughtException(RuntimeInit.java:86)
at java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:693)
at java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:690)
at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:66)
at android.os.Handler.handleCallback(Handler.java:739)?
at android.os.Handler.dispatchMessage(Handler.java:95)?
at android.os.Looper.loop(Looper.java:148)?
at android.app.ActivityThread.main(ActivityThread.java:5417)?
at java.lang.reflect.Method.invoke(Native Method)?
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)?
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)?
Caused by: java.net.ConnectException: Failed to connect to /192.168.2.12:3000
at okhttp3.internal.io.RealConnection.connectSocket(RealConnection.java:187)
at okhttp3.internal.io.RealConnection.buildConnection(RealConnection.java:170)
at okhttp3.internal.io.RealConnection.connect(RealConnection.java:111)
at okhttp3.internal.http.StreamAllocation.findConnection(StreamAllocation.java:187)
at okhttp3.internal.http.StreamAllocation.findHealthyConnection(StreamAllocation.java:123)
at okhttp3.internal.http.StreamAllocation.newStream(StreamAllocation.java:93)
at okhttp3.internal.http.HttpEngine.connect(HttpEngine.java:296)
at okhttp3.internal.http.HttpEngine.sendRequest(HttpEngine.java:248)
at okhttp3.RealCall.getResponse(RealCall.java:243)
at okhttp3.RealCall$ApplicationInterceptorChain.proceed(RealCall.java:201)
at okhttp3.RealCall.getResponseWithInterceptorChain(RealCall.java:163)
at okhttp3.RealCall.execute(RealCall.java:57)
at retrofit2.OkHttpCall.execute(OkHttpCall.java:174)
at retrofit2.adapter.rxjava.RxJavaCallAdapterFactory$RequestArbiter.request(RxJavaCallAdapterFactory.java:171)
at rx.internal.operators.OperatorSubscribeOn$1$1$1.request(OperatorSubscribeOn.java:80)
at rx.Subscriber.setProducer(Subscriber.java:209)
at rx.internal.operators.OperatorSubscribeOn$1$1.setProducer(OperatorSubscribeOn.java:76)
at rx.internal.operators.OperatorMap$MapSubscriber.setProducer(OperatorMap.java:99)
at rx.Subscriber.setProducer(Subscriber.java:205)
at retrofit2.adapter.rxjava.RxJavaCallAdapterFactory$CallOnSubscribe.call(RxJavaCallAdapterFactory.java:152)
at retrofit2.adapter.rxjava.RxJavaCallAdapterFactory$CallOnSubscribe.call(RxJavaCallAdapterFactory.java:138)
at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:50)
at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30)
at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:50)
at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30)
at rx.Observable.unsafeSubscribe(Observable.java:8460)
at rx.internal.operators.OperatorSubscribeOn$1.call(OperatorSubscribeOn.java:94)
at rx.internal.schedulers.CachedThreadScheduler$
那么长一串Retrofit内部的异常代码，这个看起来还真有点难度啊！
毕竟需要理解Retrofit的源于源码才能解决方法，而我也没时间去看。
直接把程序停止再次进来就不会有异常，才发现是程序没有完全退出导致的，所以在这里告诫大家退出程序的时候一定要确保程序是完整退出的，这个问题就不会出现了，也可以捕获异常来解决只是我觉得不是很好。