Android ListView OnScrollListener Clears old data

Question

I have created a listview using LazyAdapter.

When i scroll to the bottom of the list the new data show up but it clears all the old data.

How i can append the new data below old data?

This is my main activity code

import java.util.ArrayList;
import java.util.HashMap;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import org.w3c.dom.NodeList;

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.sax.Element;
import android.view.View;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListView;
import android.widget.TextView;

public class AndroidJSONParsingActivity extends Activity {

    // url to make request


    // JSON Node names
    static final String TAG_CONTACTS = "comics";
    static final String TAG_ID = "id";
    static final String TAG_NAME = "title";
    static final String TAG_EMAIL = "id";
    static final String TAG_PHONE_MOBILE = "image";

    // contacts JSONArray
    JSONArray contacts = null;
    ListView list;
    LazyAdapter adapter;
    static int counter = 0;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

                        // call the function
                LoadData();




    }

    public void LoadData(){
        String url = "http://myurl.com/?start=" + counter;
        // Hashmap for ListView
                ArrayList<HashMap<String, String>> contactList = new ArrayList<HashMap<String, String>>();

                // Creating JSON Parser instance
                JSONParser jParser = new JSONParser();

                // getting JSON string from URL
                JSONObject json = jParser.getJSONFromUrl(url);

                try {
                    // Getting Array of Contacts
                    contacts = json.getJSONArray(TAG_CONTACTS);

                    // looping through All Contacts
                    for(int i = 0; i < contacts.length(); i++){
                        JSONObject c = contacts.getJSONObject(i);

                        // Storing each json item in variable
                        String id = c.getString(TAG_ID);
                        String name = c.getString(TAG_NAME);
                        String email = c.getString(TAG_EMAIL);
                        String mobile = c.getString(TAG_PHONE_MOBILE);
                        // Phone number is agin JSON Object

                        // creating new HashMap
                        HashMap<String, String> map = new HashMap<String, String>();

                        // adding each child node to HashMap key => value
                        map.put(TAG_ID, id);
                        map.put(TAG_NAME, name);
                        map.put(TAG_EMAIL, email);
                        map.put(TAG_PHONE_MOBILE, mobile);

                        // adding HashList to ArrayList
                        contactList.add(map);
                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                }


                /**
                 * Updating parsed JSON data into ListView
                 * */
        list=(ListView)findViewById(R.id.list);

                // Getting adapter by passing xml data ArrayList
                adapter=new LazyAdapter(this, contactList);        
                list.setAdapter(adapter);

                // Launching new screen on Selecting Single ListItem
                list.setOnItemClickListener(new OnItemClickListener() {

                    @Override
                    public void onItemClick(AdapterView<?> parent, View view,
                            int position, long id) {
                        // getting values from selected ListItem
                        String name = ((TextView) view.findViewById(R.id.name)).getText().toString();
                        String cost = ((TextView) view.findViewById(R.id.email)).getText().toString();
                        String description = ((TextView) view.findViewById(R.id.mobile)).getText().toString();

                        // Starting new intent
                        Intent in = new Intent(getApplicationContext(), SingleMenuItemActivity.class);
                        in.putExtra(TAG_NAME, name);
                        in.putExtra(TAG_EMAIL, cost);
                        in.putExtra(TAG_PHONE_MOBILE, description);
                        startActivity(in);

                    }
                });


                list.setOnScrollListener(new OnScrollListener() {



                    @Override
                    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
                        if (view.getAdapter() != null && ((firstVisibleItem + visibleItemCount) >= totalItemCount)) {
                            //Log.v(TAG, "onListEnd, extending list");
                            //mPrevTotalItemCount = totalItemCount;
                            counter = totalItemCount;

                            LoadData();
                            adapter.notifyDataSetChanged();}
                    }

                    @Override
                    public void onScrollStateChanged(AbsListView view, int scrollState) {
                    }

                });





    }
}

And this is my LazyAdapter.java file

import java.util.ArrayList;
import java.util.HashMap;

import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class LazyAdapter extends BaseAdapter {

    private Activity activity;
    private ArrayList<HashMap<String, String>> data;

    private static LayoutInflater inflater=null;
    public ImageLoader imageLoader; 



    public LazyAdapter(Activity a, ArrayList<HashMap<String, String>> d) {
        activity = a;
        data=d;
        inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        imageLoader=new ImageLoader(activity.getApplicationContext());
    }

    public int getCount() {
        return data.size();
    }

    public Object getItem(int position) {
        return position;
    }

    public long getItemId(int position) {
        return position;
    }


    public View getView(int position, View convertView, ViewGroup parent) {
        View vi=convertView;
        if(convertView==null)
            vi = inflater.inflate(R.layout.list_row, null);

        TextView title = (TextView)vi.findViewById(R.id.title); // title
        TextView artist = (TextView)vi.findViewById(R.id.artist); // artist name
        TextView duration = (TextView)vi.findViewById(R.id.duration); // duration
        ImageView thumb_image=(ImageView)vi.findViewById(R.id.list_image); // thumb image

        HashMap<String, String> song = new HashMap<String, String>();
        song = data.get(position);



        // Setting all values in listview
        title.setText(song.get(AndroidJSONParsingActivity.TAG_NAME));
        artist.setText(song.get(AndroidJSONParsingActivity.TAG_ID));
        duration.setText(song.get(AndroidJSONParsingActivity.TAG_EMAIL));
        imageLoader.DisplayImage(song.get(AndroidJSONParsingActivity.TAG_PHONE_MOBILE), thumb_image);
        return vi;
    }
}

Answer 1

I think the problem is in your problem is that in the loadData() method. Each time you recreate the contactList..

ArrayList<HashMap<String, String>> contactList = new ArrayList<HashMap<String, String>>();

and then you call...

adapter=new LazyAdapter(this, contactList);        
list.setAdapter(adapter);

This creates a new adapter every time you load data, instead of appending data to your current adapter. You already have the adapter as an instance variable, so you do not need to initialize it every time. You should be initializing your listview and your adapter in the onCreate() method, then you never have to do it again. Then, simply add the new contact list into the existing adapter, and call notifyDataSetChanged(); and you should be good to go.