android-notifyDataSetChanged在BaseAdapter上不起作用

我有一个关于我的活动的列表视图,当我到达listview的末尾时,它调用async并使用json获取新数据.
这是async和baseAdaper代码：

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,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;
}
}

我在这里登录,当我到达listView的末尾时,它调用addAll并返回新的30项购买它没有添加到listview,我不知道为什么.

解决方法

首先,当您调用addAll()时,您已经通知了列表视图,因此不再需要此代码,请从代码中删除：

ladap.notifyDataSetChanged();

将新数据添加到列表视图数据持有者,而不是将新数据分配给列表视图数据持有者：

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

用…来代替 ：

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