android - incomplete asynctask crashes my app -

i using asynctask in of fragment , activity , these work nice. problem when press button or exit app @ time of asynchronous task execution, app crashes. log cat:

08-16 08:15:34.032: e/androidruntime(21957): fatal exception: main 08-16 08:15:34.032: e/androidruntime(21957): java.lang.illegalstateexception: can not perform action after onsaveinstancestate 08-16 08:15:34.032: e/androidruntime(21957):    @ android.support.v4.app.fragmentmanagerimpl.checkstateloss(fragmentmanager.java:1327) 08-16 08:15:34.032: e/androidruntime(21957):    @ android.support.v4.app.fragmentmanagerimpl.enqueueaction(fragmentmanager.java:1338) 08-16 08:15:34.032: e/androidruntime(21957):    @ android.support.v4.app.backstackrecord.commitinternal(backstackrecord.java:595) 08-16 08:15:34.032: e/androidruntime(21957):    @ android.support.v4.app.backstackrecord.commit(backstackrecord.java:574) 08-16 08:15:34.032: e/androidruntime(21957):    @ me.kaidul.uhunt.mainactivity.selectitem(mainactivity.java:434) 08-16 08:15:34.032: e/androidruntime(21957):    @ me.kaidul.uhunt.mainactivity.access$0(mainactivity.java:387) 08-16 08:15:34.032: e/androidruntime(21957):    @ me.kaidul.uhunt.mainactivity$getproblemlisttask.onpostexecute(mainactivity.java:680) 08-16 08:15:34.032: e/androidruntime(21957):    @ me.kaidul.uhunt.mainactivity$getproblemlisttask.onpostexecute(mainactivity.java:1) 08-16 08:15:34.032: e/androidruntime(21957):    @ android.os.asynctask.finish(asynctask.java:417) 08-16 08:15:34.032: e/androidruntime(21957):    @ android.os.asynctask.access$300(asynctask.java:127) 08-16 08:15:34.032: e/androidruntime(21957):    @ android.os.asynctask$internalhandler.handlemessage(asynctask.java:429) 08-16 08:15:34.032: e/androidruntime(21957):    @ android.os.handler.dispatchmessage(handler.java:99) 08-16 08:15:34.032: e/androidruntime(21957):    @ android.os.looper.loop(looper.java:123) 08-16 08:15:34.032: e/androidruntime(21957):    @ android.app.activitythread.main(activitythread.java:4627) 08-16 08:15:34.032: e/androidruntime(21957):    @ java.lang.reflect.method.invokenative(native method) 08-16 08:15:34.032: e/androidruntime(21957):    @ java.lang.reflect.method.invoke(method.java:521) 08-16 08:15:34.032: e/androidruntime(21957):    @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:868) 08-16 08:15:34.032: e/androidruntime(21957):    @ com.android.internal.os.zygoteinit.main(zygoteinit.java:626) 08-16 08:15:34.032: e/androidruntime(21957):    @ dalvik.system.nativestart.main(native method) 

i not adding here asynctask code working without pressing button or exiting app. call asynctask new gettaskdone().execute(parameter) , there onpostexecute in every asyctask.

how can avoid app crashing ?

edit:

now thinking that, problem might not in asynctask. because other asynctask working regardless of backpress/exit.

this problematic asynctask:

protected class getproblemlisttask extends asynctask {

@override protected void doinbackground(string... params) {     inputstreamreader isr = null;     if (hasconnection) {         date date = new date();         long savedtime = prefs.getlong(commonutils.last_saved,                 date.gettime());         long = date.gettime();         if (now - savedtime > fivedays                 || (now - savedtime <= fivedays && prefs.getboolean(                         commonutils.problemlistiscached, false) == false)) {             if (commonutils.isdebuggable) {                 log.d("updating", "need update!");             }             prefs.edit()                     .putboolean(commonutils.problemlistiscached, false)                     .commit();             isr = new jsondownloader().getjsonstringfromurl(params[0]);             bufferedreader br = new bufferedreader(isr, buffersize);             stringbuilder sb = new stringbuilder();             string line = null;             try {                 while ((line = br.readline()) != null) {                     sb.append(line + "\n");                 }             } catch (ioexception e) {                 log.d("problem", "in file writting");             }             writetofile(sb.tostring(), commonutils.file_problem_list);             prefs.edit()                     .putboolean(commonutils.problemlistiscached, true)                     .commit();             try {                 isr.close();             } catch (ioexception e) {                 if (commonutils.isdebuggable) {                     log.d("isr", e.tostring());                 }             }             try {                 br.close();             } catch (ioexception e) {                 if (commonutils.isdebuggable) {                     log.d("br", e.tostring());                 }             }             prefs.edit().putlong(commonutils.last_saved, now).commit();         } else {             if (commonutils.isdebuggable) {                 log.d("old_copy", "old copy rendering");             }             try {                 isr = new inputstreamreader(                         openfileinput(commonutils.file_problem_list));             } catch (filenotfoundexception e) {                 log.d("file_not_found", "file missing!");             }         }     } else {         try {             isr = new inputstreamreader(                     openfileinput(commonutils.file_problem_list));         } catch (filenotfoundexception e) {             log.d("file_not_found", "file missing!");         }     }     if (commonutils.isdebuggable) {         log.d("start", "mapping start");     }     try {         isr = new inputstreamreader(                 openfileinput(commonutils.file_problem_list));     } catch (filenotfoundexception e1) {      }     jsonreader reader = new jsonreader(isr);     try {         reader.beginarray();         while (reader.hasnext()) {             reader.beginarray();             problems.put(                     reader.nextint(),                     new problems(reader.nextstring(), reader                             .nextstring(), reader.nextint()));             while (reader.hasnext())                 reader.skipvalue();             reader.endarray();         }         reader.endarray();         reader.close();     } catch (ioexception e) {         if (commonutils.isdebuggable) {             log.d("problems", "hashmaping problem");         }     }     return null; }  @override protected void onpostexecute(void result) {     getsupportactionbar().sethomebuttonenabled(true);     getsupportactionbar().setdisplayhomeasupenabled(true);  // selecitem() function. it's task add fragment activity.      selectitem(0);     if (commonutils.isdebuggable) {         log.d("successful", "eventually survived!");     } } 

}

asynctask's onpreexecute , onpostexecute run on ui thread. i'm assuming you're not retaining instance of asynctask , calling cancel on in fragment/activity's ondestroy.

either add that, or add boolean flag stating if app visible or not (api 17 introduced activity.isdestroyed(), if you're using api level >= 17 use that).

note: if add call cancel asynctask, you'll still need call along lines of:

if(iscancelled()) { return; } 

in beginning of onpostexecute.

edit: more complete example of iscancelled() method:

in activity:

protected void ondestroy() {     super.ondestroy();      if(task != null && task.getstatus() != asynctask.status.finished) {         task.cancel(true);     } } 

and assign task class-wide variable, can add task = line that's doing new asynctask().execute(); , it'll work now.

according documentation asynctask.cancel() guarantees onpostexecute never called don't need iscancelled() check in there stated previously.