Lag with asynctask when load data from firebase

问题

I'm trying to use asink task to download the data from the background firebase and use them to create a non-proprietary firebase recyclerview. However, lags after the postexecute remain the same. I do not know if what I did is right.  

What am I doing wrong?

public class FriendFragmentFollow extends Fragment {

FriendHoldAdapter3 adapter;
RecyclerView recyclerView;
ArrayList<FriendItem> username;
ArrayList<String> uid, url;
DatabaseReference mDatabase;

@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,
                         @Nullable Bundle savedInstanceState) {


    return inflater.inflate(R.layout.friend_fragment_follow, container, false);

}

@Override
public void onViewCreated(final View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    SearchView search = (SearchView) view.findViewById(R.id.ciao);

    mDatabase = FirebaseDatabase.getInstance().getReference();


    recyclerView = (RecyclerView) view.findViewById(R.id.friend_list2);
    //recyclerView.setLayoutManager(new LinearLayoutManager(getApplicationContext()));
    recyclerView.setLayoutManager(new GridLayoutManager(view.getContext(), 2));


    new LongOperation().execute("");


    search.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
        @Override
        public boolean onQueryTextSubmit(String query) {

            return true;
        }

        @Override
        public boolean onQueryTextChange(String newText) {
            if (newText.equals("")){
                newText = "             ";
            }
            if (newText.equals("View All")){
                newText = "";
            }
            final List<FriendItem> filteredModelList = filter(username, newText);
            adapter.setFilter(filteredModelList);
            return true;
        }

    });


}


public String getUid() {
    return FirebaseAuth.getInstance().getCurrentUser().getUid();
}

private class LongOperation extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... params) {

        final DatabaseReference mPostReference = FirebaseDatabase.getInstance().getReference().child("user-profile");
        mPostReference.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {



                username = new ArrayList<>();
                uid = new ArrayList<String>();
                url = new ArrayList<String>();

                for (DataSnapshot data : dataSnapshot.getChildren()){
                    final FriendItem friendItem = data.getValue(FriendItem.class);
                    //final String friendItem2 = data.getKey();



                    username.add(friendItem);
                    //uid.add(friendItem2);
                    adapter = new FriendHoldAdapter3(getContext(), username, uid, url);
                    //adapter.setClickListener(FriendActivity3.this);
                    recyclerView.setAdapter(adapter);

                    /**
                     adapter = new FriendHoldAdapter2(FriendActivity2.this, username, uid);
                     adapter.setClickListener(FriendActivity2.this);
                     recyclerView.setAdapter(adapter);
                     **/
                    final List<FriendItem> filteredModelList = filter(username, "        ");
                    adapter.setFilter(filteredModelList);



                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
            }});

        return "Executed";
    }

    @Override
    protected void onPostExecute(String result) {
        Toast.makeText(getContext(), "Post execute", Toast.LENGTH_SHORT).show();


    }

    @Override
    protected void onPreExecute() {}

    @Override
    protected void onProgressUpdate(Void... values) {}
}

回答1:

You should use AyncTask inside the onDataChange() method. You only need to do the processing part in the background thread after you get the data from onDataChanged. Try

final DatabaseReference mPostReference = FirebaseDatabase.getInstance()
               .getReference().child("user-profile");
mPostReference.addListenerForSingleValueEvent(new ValueEventListener() 
{
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
             new LongOperation().execute(dataSnapshot);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
});

private class LongOperation extends AsyncTask<DataSnapshot, Void, String> {

@Override
protected String doInBackground(DataSnapshot... params) {

            for (DataSnapshot data : params[0].getChildren()){
                final FriendItem friendItem = data.getValue(FriendItem.class);
                //final String friendItem2 = data.getKey();



                username.add(friendItem);
                //uid.add(friendItem2);



            }
    return "Executed";
}

@Override
protected void onPostExecute(String result) {
                 adapter = new FriendHoldAdapter3(getContext(), username, uid, url);
                //adapter.setClickListener(FriendActivity3.this);
                recyclerView.setAdapter(adapter);

                /**
                 adapter = new FriendHoldAdapter2(FriendActivity2.this, username, uid);
                 adapter.setClickListener(FriendActivity2.this);
                 recyclerView.setAdapter(adapter);
                 **/
                final List<FriendItem> filteredModelList = filter(username, "        ");
                adapter.setFilter(filteredModelList);

    Toast.makeText(getContext(), "Post execute", Toast.LENGTH_SHORT).show();


}

@Override
protected void onPreExecute() {
      username = new ArrayList<>();
      uid = new ArrayList<String>();
      url = new ArrayList<String>();
}

@Override
protected void onProgressUpdate(Void... values) {}
}

来源：https://stackoverflow.com/questions/46144916/lag-with-asynctask-when-load-data-from-firebase