Does AsynckTask.onPostExecute and FragmentActivity.onResumeFragments run on same thread (ui thread)?

Question

I get ConcurrentModificationException when I traverse the ArrayList. What I did:

1.  activity has a ArrayList<Callable>
2.  add Callable to ArrayList when AsyncTask.onPostExecute
3.  traverse the ArrayList to call the callable in onResumeFragments

How the exception be triggered: I make the AsyncTask.execute() and press home button quickly, when my app come back to foreground, the exception happened.

What confuses me is: if AsyncTask.onPostExecute and FragmentActivity.onResumeFragments run on same thread, there won't be a java.util.ConcurrentModificationException, right?

As I know AsyncTask.onPostExecute runs on ui thread, and FragmentActivity.onResumeFragments should runs on ui thread too, so how java.util.ConcurrentModificationException happend?

This is my exception stack

com.yumei.sdkdemo I/PayMethodActivity: 
  11-10 11:34:35.218 10030-10030/com.yumei.sdkdemo E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.yumei.sdkdemo, PID: 10030
java.lang.RuntimeException: Unable to resume activity {com.yumei.sdkdemo/com.yumei.sdk.PayMethodActivity}: java.util.ConcurrentModificationException
 at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2954)
 at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2985)
 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1327)
 at android.os.Handler.dispatchMessage(Handler.java:102)
 at android.os.Looper.loop(Looper.java:135)
 at android.app.ActivityThread.main(ActivityThread.java:5235)
 at java.lang.reflect.Method.invoke(Native Method)
 at java.lang.reflect.Method.invoke(Method.java:372)
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:906)
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:701)
 Caused by: java.util.ConcurrentModificationException
 at java.util.ArrayList$ArrayListIterator.next(ArrayList.java:573)
 at com.yumei.sdk.PayMethodFragmentActivity.onResumeFragments(PayMethodActivity.java:116)
 at android.support.v4.app.FragmentActivity.onPostResume(FragmentActivity.java:451)
 at android.support.v7.app.AppCompatActivity.onPostResume(AppCompatActivity.java:141)
 at android.app.Activity.performResume(Activity.java:6040)
 at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2943)
 at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2985) 
 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1327) 
 at android.os.Handler.dispatchMessage(Handler.java:102) 
 at android.os.Looper.loop(Looper.java:135) 
 at android.app.ActivityThread.main(ActivityThread.java:5235) 
 at java.lang.reflect.Method.invoke(Native Method) 
 at java.lang.reflect.Method.invoke(Method.java:372) 
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:906) 
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:701)

thanks for your response.

`onPostExecute` runs on the thread from which you call the `asyncTask.execute()` method from — Bhargav, Nov 10 '15 at 06:46
Can you post some code samples as no one can help you by only reading the stack trace. — Kiril Aleksandrov, Nov 10 '15 at 11:18

score 1 · Answer 1 · answered Nov 10 '15 at 11:03

1

Notice that if you want to delete some items while traverse, you should you Iterator. And if your AsynTask was not created on UI thread, make sure you use thread-safe.

answered Nov 10 '15 at 11:03

duynt

128
8

score 1 · Answer 2 · answered Nov 10 '15 at 11:13

Yes, AsyncTask's onPostexcute is run in UI thread, and I dont think it's thread problem. ConcurrentModificationException maybe occurs when you try to modify your Arraylist while looping its elements (such as remove Callable in side for loop).
p/s: you should post your onPostExcute code with your logcat.

Does AsynckTask.onPostExecute and FragmentActivity.onResumeFragments run on same thread (ui thread)?

2 Answers2