java.lang.IllegalStateException for Android version 4.4.4

Question

I am working with adapters in Android and in rare scenario's the app is crashing while setting data for ListView ...Please Help out. The Exception is as follows

java.lang.IllegalStateException: The content of the adapter has 
    changed but ListView did not receive a notification. Make sure the content of your 
    adapter is not modified from a background thread, but only from the UI thread.
     Make sure your adapter calls notifyDataSetChanged() when its content changes.
     [in ListView(2131558745, class android.widget.ListView)
     with Adapter(class com.adapters.CustomToBeSyncAdapter)

Here is My code snippet

private class ImportAsyncTask extends AsyncTask<Void, Integer, Integer> {

                @Override
                protected Integer doInBackground(Void... params) {
                    Realm realm = Realm.getDefaultInstance();

                    realm.executeTransaction(new Realm.Transaction() {
                        @Override
                        public void execute(Realm realm) {
                            try {
                                RealmResults<AssetsActivitiesRealm> mResultsActivities = realm.where(AssetsActivitiesRealm.class).findAll();
                                for (int i = 0; i < mResultsActivities.size(); i++) {
                                    AssetsActivitiesRealm mAssetsActivitiePj = mResultsActivities.get(i);
                                        SyncPojoList.add(new SyncPojo(mAssetsActivitiePj.getBatch(), mAssetsActivitiePj.getItemCode()));
                                }
                            } catch (Exception e) {
                                e.printStackTrace();
                            }
                        }
                    });
                    realm.close();
                    return 1;
                }

                @Override
                protected void onPreExecute() {
                    showLoading();
                }

                @Override
                protected void onPostExecute(Integer sum) {
                    try {
                        cancelLoading();
                        displayListView();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }

            private void notifyAdapter() {
                getActivity().runOnUiThread(new Runnable() {
                    public void run() {
                        listViewSync.setAdapter(null);
                        if (mdataAdapter != null) {
                            mdataAdapter.notifyDataSetChanged();
                            listViewSync.requestLayout();
                        }
                    }
                });
            }

            private void displayListView() {
                    mdataAdapter = new CustomToBeSyncAdapter(getActivity(),
                            R.layout.custom_tobesync_row, SyncPojoList);
                    notifyAdapter();
                    listViewSync.setAdapter(mdataAdapter);
                    listViewSync.invalidate();
            }

Answer 1

As you're adding objects inside the AsyncTask#doInBackground() you're still changing the model of the ListView 's adapter from a background thread.

Try using the AsyncTask#publishProgress(Progress...) inside your for-loop and then override AsyncTask#onProgressUpdate(Progress...) where Progress is your model.

So your for-loop could look something like this:

RealmResults<AssetsActivitiesRealm> mResultsActivities = realm.where(AssetsActivitiesRealm.class).findAll();
for (int i = 0; i < mResultsActivities.size(); i++) {
    AssetsActivitiesRealm mAssetsActivitiePj = mResultsActivities.get(i);
    publishProgress(new SyncPojo(mAssetsActivitiePj.getBatch(), mAssetsActivitiePj.getItemCode());
}

And your onProgressUpdate could look like this:

public void onProgressUpdate(SyncPojo progress) {
    SyncPojoList.add(progress);
    mdataAdapter.notifyDataSetChanged(); // Notifying changes to the adapter here.
}

It's not clear why you need to run all of this inside an AsyncTask and Realm actually advertises that you don't really need to run queries inside a background thread, as their querying is so fast (they're using lazy-loading when getting data) that it should affect the UI thread in most cases - especially when you don't have any "special" queries at all.

On another note, you don't need to create a Realm.Transaction to query the data. Transactions are only used to ensure correctness when changing data.

You could definitely simplify your code a lot:

• You're using requestLayout on your ListView after calling notifyDatasetChanged which is probably useless.
• You're using general try-catch with Exception for what reason? You should handle the code before it can lead to an exception instead of just adding a try-catch around the error prone code.
• Your AsyncTask returns a meaningless integer instead of actually returning the result for instance.
• setting the adapter will also notify the ListView to be updated, so no need to call your notifyAdapter .
• The notifyAdapter method is doing a lot of things, that it doesn't need to do - setting the adapter to null for instance.

Hope this helps, else I'll be happy to elaborate on any areas.