EmPubLite app crashing on Tutorial #13

Question

So, I am going through the Tutorial #12 and everything is working fine. I then try to go onto Tutorial #13 for Saving/Restoring Last-Read Position and the app crashes:

04-10 15:59:26.510: E/Trace(704): error opening trace file: No such file or directory (2)
04-10 15:59:27.491: D/AndroidRuntime(704): Shutting down VM
04-10 15:59:27.491: W/dalvikvm(704): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
04-10 15:59:27.500: E/AndroidRuntime(704): FATAL EXCEPTION: main
04-10 15:59:27.500: E/AndroidRuntime(704): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.commonsware.empublite/com.commonsware.empublite.EmPubLiteActivity}: java.lang.NullPointerException
04-10 15:59:27.500: E/AndroidRuntime(704):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
04-10 15:59:27.500: E/AndroidRuntime(704):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
04-10 15:59:27.500: E/AndroidRuntime(704):  at android.app.ActivityThread.access$600(ActivityThread.java:130)
04-10 15:59:27.500: E/AndroidRuntime(704):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
04-10 15:59:27.500: E/AndroidRuntime(704):  at android.os.Handler.dispatchMessage(Handler.java:99)
04-10 15:59:27.500: E/AndroidRuntime(704):  at android.os.Looper.loop(Looper.java:137)
04-10 15:59:27.500: E/AndroidRuntime(704):  at android.app.ActivityThread.main(ActivityThread.java:4745)
04-10 15:59:27.500: E/AndroidRuntime(704):  at java.lang.reflect.Method.invokeNative(Native Method)
04-10 15:59:27.500: E/AndroidRuntime(704):  at java.lang.reflect.Method.invoke(Method.java:511)
04-10 15:59:27.500: E/AndroidRuntime(704):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
04-10 15:59:27.500: E/AndroidRuntime(704):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-10 15:59:27.500: E/AndroidRuntime(704):  at dalvik.system.NativeStart.main(Native Method)
04-10 15:59:27.500: E/AndroidRuntime(704): Caused by: java.lang.NullPointerException
04-10 15:59:27.500: E/AndroidRuntime(704):  at com.commonsware.empublite.ModelFragment.executeAsyncTask(ModelFragment.java:51)
04-10 15:59:27.500: E/AndroidRuntime(704):  at com.commonsware.empublite.ModelFragment.deliverModel(ModelFragment.java:38)
04-10 15:59:27.500: E/AndroidRuntime(704):  at com.commonsware.empublite.ModelFragment.onActivityCreated(ModelFragment.java:29)
04-10 15:59:27.500: E/AndroidRuntime(704):  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:891)
04-10 15:59:27.500: E/AndroidRuntime(704):  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1080)
04-10 15:59:27.500: E/AndroidRuntime(704):  at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:622)
04-10 15:59:27.500: E/AndroidRuntime(704):  at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1416)
04-10 15:59:27.500: E/AndroidRuntime(704):  at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:505)
04-10 15:59:27.500: E/AndroidRuntime(704):  at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1163)
04-10 15:59:27.500: E/AndroidRuntime(704):  at android.app.Activity.performStart(Activity.java:5018)
04-10 15:59:27.500: E/AndroidRuntime(704):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2032)
04-10 15:59:27.500: E/AndroidRuntime(704):  ... 11 more

I tried to comment out the code I did until the last point that it was working, but that didn't seem to work. I am not really sure how to read this stack trace either. What should I be looking at to fix this problem?

Thanks.

Answer 1

I am not really sure how to read this stack trace either. What should I be looking at to fix this problem?

Line 51 of ModelFragment.java, in the executeAsyncTask() method is where you are crashing (see last stack trace stanza, starting with Caused by: java.lang.NullPointerException).

Your line numbers and those in the answers are not completely lining up. However, the only way executeAsyncTask() could have a NullPointerException is if the AsyncTask you are passing in is null, and that should not be possible as you define those tasks immediately before calling executeAsyncTask() in the deliverModel() method. Perhaps you missed a line in deliverModel().