RecyclerView blocks UI when setting the adapter

Question

I have a requirement in which I have a populated database with over 300k rows. I have successfully implemented a CursorAdapter based in this question, with a mix of the two most up voted answers HERE.

I have implemented an AsyncTask for background service to perform the query to the database which is very fast, doesn't take more than 2-3 seconds. My ProgressDialog from the AsyncTask is at times hard to detect.

My problem is, when the task is done and I retrieve the Cursor, when I set the Adapter to the RecyclerView, the process freezes my UI for a few seconds until the data is set. It also happens when I perform a search (new query, same procedure as getting all the rows but with fewer rows), and replace the Cursor to update the data.

Here is some relevant code:

AsyncTask

@Override
protected Void doInBackground(Void... Void) {
    if(type==Constants.GET_ZIP_CODES)
        cursor = db.getAllZipCodes();
    else
        cursor = db.searchZipCodes(text);

    return null;
}

@Override
protected void onPostExecute(Void Void) {
    setAdapter();
    mProgressDialog.dismiss();
    super.onPostExecute(Void);
}

Methods

private void setAdapter(){
    if(myAdapter == null){
        myAdapter = new MyAdapter(getActivity(), cursor);
        search_rv.setAdapter(myAdapter);
    } else
        myAdapter.swapCursor(cursor);
}

Since it is a search I don't have much to do here besides notifyDataSetChanged() because all the data changes widely in every search.

Is this normal? Since a RecyclerView only renders the visible views, why does it freeze and takes so long to update since the Cursor is already ready from the AsyncTask?

EDIT

I have changed my Adapter to avoid using CursorAdapter as @cricket_007 pointed out having an Adapter within an Adapter is bad design.

This is my Adapter:

public class SearchListAdapter extends RecyclerView.Adapter<SearchListAdapter.ViewHolder> {


private Context mContext;

private Cursor mCursor;

private boolean mDataValid;
private int mRowIdColumn;

private DataSetObserver mDataSetObserver;

public SearchListAdapter(Context context, Cursor c) {

    mContext = context;
    mCursor=c;

    mDataValid = c != null;
    mRowIdColumn = mDataValid ? mCursor.getColumnIndex("_id") : -1;
    mDataSetObserver = new NotifyingDataSetObserver();
    if (mCursor != null) {
        mCursor.registerDataSetObserver(mDataSetObserver);
    }

}

static class ViewHolder extends RecyclerView.ViewHolder {
    TextView itemTV;

    ViewHolder(View itemView) {
        super(itemView);
        itemTV = (TextView) itemView.findViewById(R.id.itemTV);
    }
}


@Override
public void setHasStableIds(boolean hasStableIds) {
    super.setHasStableIds(true);
}

@Override
public int getItemCount() {
    if (mDataValid && mCursor != null) {
        return mCursor.getCount();
    }
    return 0;
}

@Override
public void onBindViewHolder(ViewHolder holder, int position) {
    // Passing the binding operation to cursor loader
    mCursor.moveToPosition(position);
    String town = mCursor.getString(mCursor.getColumnIndex(Constants.COLUMN_TOWN));
    String zipcode = mCursor.getString(mCursor.getColumnIndex(Constants.COLUMN_ZIPCODE));
    String zipcode_etx = mCursor.getString(mCursor.getColumnIndex(Constants.COLUMN_ZIPCODE_EXTENSION));
    holder.itemTV.setText(zipcode+"-"+zipcode_etx+", "+town);

}

@Override
public SearchListAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.fragment_search_list_item,parent,false);
    // Passing the inflater job to the cursor-adapter
    return new SearchListAdapter.ViewHolder(itemView);
}

public void swapCursor(Cursor cursor) {
    Cursor old = changeCursor(cursor);
    if (old != null) {
        old.close();
    }
}

private Cursor changeCursor(Cursor newCursor) {
    if (newCursor == mCursor) {
        return null;
    }
    final Cursor oldCursor = mCursor;
    if (oldCursor != null && mDataSetObserver != null) {
        oldCursor.unregisterDataSetObserver(mDataSetObserver);
    }
    mCursor = newCursor;
    if (mCursor != null) {
        if (mDataSetObserver != null) {
            mCursor.registerDataSetObserver(mDataSetObserver);
        }
        mRowIdColumn = newCursor.getColumnIndexOrThrow("_id");
        mDataValid = true;
        notifyDataSetChanged();
    } else {
        mRowIdColumn = -1;
        mDataValid = false;
        notifyDataSetChanged();
    }
    return oldCursor;
}

private class NotifyingDataSetObserver extends DataSetObserver {
    @Override
    public void onChanged() {
        super.onChanged();
        mDataValid = true;
        notifyDataSetChanged();
    }

    @Override
    public void onInvalidated() {
        super.onInvalidated();
        mDataValid = false;
        notifyDataSetChanged();
    }
}


}

Cursor cursor is a class variable. I only make use of it in these methods plus the Adapter. The adapter itself is pretty much the same plus the `swapCursor` method — Ricardo, Sep 09 '17 at 02:58
Having an adapter in an adapter sounds like poor design decision — OneCricketeer, Sep 09 '17 at 03:01
The progress dialog dismisses really fast, but the list updates a few seconds later with the UI frozen — Ricardo, Sep 09 '17 at 03:07
I have updated my answer, if you care to take a look, i would appreciate — Ricardo, Sep 09 '17 at 03:27

score 1 · Accepted Answer · answered Sep 09 '17 at 12:15

Well, I found out why this was happening and the reason is weird. The problem has nothing to do with the RecyclerView but with the way the data is fetch.

In my AsyncTask, where I fetch the data, I wrote a Log.d to print the Cursor size like so:

@Override
protected Void doInBackground(Void... Void) {
    if(type==Constants.GET_ZIP_CODES)
        cursor = db.getAllZipCodes();
    else
        cursor = db.searchZipCodes(text);

    Log.d("DATABASE","SIZE   "+cursor.getCount());
    return null;
}

This made the AsyncTask take longer, the ProgressDialog takes longer to go off. What I understand is that somehow, the database query is performed, the code keeps compiling, but the data is only ready in the Cursor after a while. Once I printed the result just after the query, it didn't go past the line until the cursor was fully loaded.

score 0 · Answer 2 · answered Sep 09 '17 at 05:02

Actually this is not an answer(Would have put it in comment if i had enough reputation points) just a suggestion/case study i came across while loading data from database to recyclerView. Instead of directly sending the cursor over to adapter i sent it as an arraylist, but thats besides the point.

The place where i got the freeze like you seem to get is when i have to load a text with over 700-800 character into a card. So when i crop the text to less than 600 the freeze vanishes.

So just check if you have any data with large character set, if so try removing that and test it out.

Hope it works for you, suggestion put read more option for large text like whatsapp does!

Thanks for your suggestion but no, I don't have any entry that has more than about 20 characters — Ricardo, Sep 09 '17 at 11:58

RecyclerView blocks UI when setting the adapter

2 Answers2