android-notifyDataSetChanged doesn't work on BaseAdapter

Question

i've a listview on my activity , when I reach the end of listview , it calls async and it getting new data using json . this is the async and baseAdaper codes :

ListAdapter ladap;

private class GetContacts AsyncTask<Void, Void,ArrayList<HashMap<String, String>>> {    
@Override
protected Void doInBackground(Void... arg0) {
    Spots_tab1_json sh = new Spots_tab1_json();
    String jsonStr = sh.makeServiceCall(url + page, Spots_tab1_json.GET);

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

    if (jsonStr != null) {
        try {
            JSONObject jsonObj = new JSONObject(jsonStr);
            contacts = jsonObj.getJSONArray(TAG_CONTACTS);

                for (int i = 0; i < contacts.length(); i++) {
                JSONObject c = contacts.getJSONObject(i);
                String id = new String(c.getString("id").getBytes("ISO-8859-1"), "UTF-8");
                String dates = new String(c.getString("dates").getBytes("ISO-8859-1"), "UTF-8");
                String price = new String(c.getString("gheymat").getBytes("ISO-8859-1"), "UTF-8");
                HashMap<String, String> contact = new HashMap<String, String>();
                contact.put("id", id);
                contact.put("dates", dates);
                contact.put("price", price);
                dataC.add(contact);
            }
            }
        } catch (JSONException e) {
            goterr = true;
        } catch (UnsupportedEncodingException e) {
            goterr = true;
        }
    } else {
        goterr = true;
    }
    return dataC;
}

@Override
protected void onPostExecute(ArrayList<HashMap<String, String>> result) {
    super.onPostExecute(result);
    if (!isCancelled() && goterr == false) {
        if(ladap==null){
            ladap=new ListAdapter(MainActivity.this,result);
            lv.setAdapter(ladap);
        }else{
            ladap.addAll(result);
            ladap.notifyDataSetChanged();
        }

}

}

public class ListAdapter extends BaseAdapter {
Activity activity;
public ArrayList<HashMap<String, String>> list;

public ListAdapter(Activity activity,ArrayList<HashMap<String, String>> list) {
    super();
    this.activity = (Activity) activity;
    this.list = list;
}

public void addAll(ArrayList<HashMap<String, String>> result) {
    Log.v("this",result.size()+" resultsize");
    this.list = result;
    notifyDataSetChanged();
}

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

public Object getItem(int position) {
    return contactList.get(position);
}

public long getItemId(int arg0) {
    return 0;
}

private class ViewHolder {
    TextView title,price;
    ImageView img ; 
    //RelativeLayout rl; 
}

public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder;
    LayoutInflater inflater = activity.getLayoutInflater();
    if (convertView == null) {
        convertView = inflater.inflate(R.layout.item, null);
        holder = new ViewHolder();
        holder.title = (TextView) convertView.findViewById(R.id.title);
        holder.price = (TextView) convertView.findViewById(R.id.price);
        convertView.setTag(holder);
    } else {
        holder = (ViewHolder) convertView.getTag();
    }

        item = contactList.get(position);
        holder.price.setText(item.get("price"));
    return convertView;
}
}

I logged here , when I reach the end of listView , it calls addAll and it returns new 30 items buy it doesn't added to listview , I don't know why .

Answer 1

First of all you have already notify your list view when you call addAll() so this code no longer required please remove from your code :

ladap.notifyDataSetChanged();

Add new data to list view data holder instead of assign new data to list view data holder :

public void addAll(ArrayList<HashMap<String, String>> result) {
    Log.v("this",result.size()+" resultsize");
    this.list = result;
    notifyDataSetChanged();
}

Replace with :

public void addAll(ArrayList<HashMap<String, String>> result) {
    Log.v("this",result.size()+" resultsize");
    if(list==null){
      list = new ArrayList<HashMap<String, String>>();
    }
    list.addAll(result)
    notifyDataSetChanged();
}

Answer 2

Try to change this :

public void addAll(ArrayList<HashMap<String, String>> result) {
    Log.v("this",result.size()+" resultsize");
    this.list = result;
    notifyDataSetChanged();
}

To :

public void addAll(ArrayList<HashMap<String, String>> result) {
    Log.v("this",result.size()+" resultsize");
    for(int i = 0;i < result.size(); i++)
       list.add(result.get(i));
    //notifyDataSetChanged(); //no need to call again here
}

The point is, i think this.list = result; will delete the old items before adding a new item.