Concurrent modification in RecyclerView

Question

I've got a problem with removing items from List in RecyclerView. It contains list of checked items. I want to uncheck one item of the list.

So, method removeGroupItem() removes item from list of checked items. Here it is:

private void removeGroupItem(String groupId) {
    for (String group : pickedGroups) {
        if (group.equals(groupId))
            pickedGroups.remove(group);
    }
}

If I tap very fast 2-3 times on some item - it crashes. Here is stacktrace:

java.util.ConcurrentModificationException
        at java.util.ArrayList$Itr.next(ArrayList.java:860)
        at com.camness.vidimguploadjun2016.trips.group_adapter.GroupsAdapter.removeGroupItem(GroupsAdapter.java:76)
        at com.camness.vidimguploadjun2016.trips.group_adapter.GroupsAdapter.access$300(GroupsAdapter.java:16)
        at com.camness.vidimguploadjun2016.trips.group_adapter.GroupsAdapter$GroupViewHolder.lambda$new$0$GroupsAdapter$GroupViewHolder(GroupsAdapter.java:65)
        at com.camness.vidimguploadjun2016.trips.group_adapter.GroupsAdapter$GroupViewHolder$$Lambda$0.onClick(Unknown Source:2)
        at android.view.View.performClick(View.java:6303)
        at android.widget.CompoundButton.performClick(CompoundButton.java:134)
        at android.view.View$PerformClick.run(View.java:24828)
        at android.os.Handler.handleCallback(Handler.java:789)
        at android.os.Handler.dispatchMessage(Handler.java:98)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6798)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

Thank you all in advance for any help.

Yes, you can't remove from an ordinary collection while iterating over it like that. You'll need to iterate with an Iterator and use its remove() method. — Markus Kauppinen, Aug 31 '18 at 09:40

score 1 · Answer 1 · answered Aug 31 '18 at 10:15

First of all change the logic of work. For example you can break after remove

    for (String group : pickedGroups) {
        if (group.equals(groupId)) {
            pickedGroups.remove(group);
            break;
        }
    }

But you also have to synchronize the threads which have access to this array. For example

    synchronized(pickedGroups) {
       for (String group : pickedGroups) {
           if (group.equals(groupId)) {
               pickedGroups.remove(group);
               break;
           }
       }
    }

if you break it, the for loop won't work after because you exit it. which means, only first one gets removed. — c-an, Apr 18 '20 at 13:47

Concurrent modification in RecyclerView

1 Answers1