如何为聊天应用程序在android中更新新消息的listview

Question

i'm using the listview for the showing the chat, in that i used asynctask to retrieve the message from the database and then i populate the message in the item using adapter and arraylist. then how to update the listview for the every new message and how to maintain the scroll position and how to show the notification for the new message in the title in android.

this is my chat activity

 public class ChatActivity extends Activity implements OnScrollListener {
        ListView listview;

        MessageTask task;
        Handler handler;
        ArrayList<String> tExp=new ArrayList<String>();
        Boolean loadingMore = true;
        List list = new ArrayList();
        Boolean stopLoadingData = false;

        EditText edit;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_chat);

             txt=(TextView)findViewById(R.id.roomname);
            listview =(ListView)findViewById(R.id.messagelist);
             edit=(EditText)findViewById(R.id.editText1);

             txt.setText(message);

             task = new MessageTask();
             task.execute(new String[]{URL});


        }



     class MessageTask extends AsyncTask<String, Void, List<String>> {

             private final HttpClient Client = new DefaultHttpClient();

            @TargetApi(Build.VERSION_CODES.HONEYCOMB)
            @Override
            protected List<String> doInBackground(String... params) {

                String output = "";
               for(String out:params){

                     try{
                     HttpGet httpget = new HttpGet(out);
                     ResponseHandler<String> responseHandler = new BasicResponseHandler();
                     output = Client.execute(httpget, responseHandler);

                       try {


                        JSONObject jObject= new JSONObject(output);
                        JSONArray menuObject = new JSONArray(jObject.getString("response"));   

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

                      for (int i = 0; i<menuObject.length(); i++)
                      {

                         list.add(menuObject.getJSONObject(i).getString("fk_username_c").toString()+" "+menuObject.getJSONObject(i).getString("message_c").toString());     

                     }
                      adapter=new ArrayAdapter<String>(ChatActivity.this,android.R.layout.simple_list_item_1);

                       } catch (JSONException e) {
                           Log.e("log_tag", "Error parsing data ");
                       }
                     }catch(Exception e){
                         Log.i("Animation", "Thread  exception " );
                     }
               }

              return list;

            }


    @Override      
    protected void onPostExecute(List<String> list) {


          adapter.notifyDataSetChanged();
          listview.setAdapter(adapter);
          adapter.clear();
         listview.clearTextFilter();
          adapter.addAll(list);
          loading=false;

     }
    }


        @Override
        public boolean onCreateOptionsMenu(Menu menu) {
            // Inflate the menu; this adds items to the action bar if it is present.
            getMenuInflater().inflate(R.menu.chat, menu);
            return true;
        }

    }

plz help me how to update the listview only for the every new message is arrived in the database.

Answer 1

You will need to update list content in onProgressUpdate method

ArrayList<Message> messages;
@Override
        public void onProgressUpdate(String... v) {

            /*
             * check wether we have already added a status message
             */
            if (messages.get(messages.size() - 1).isStatusMessage) {
                /*
                 * update the status for that
                 */
                messages.get(messages.size() - 1).setMessage(v[0]);
                adapter.notifyDataSetChanged();
                getListView().setSelection(messages.size() - 1);
            } else {
                /*
                 * add new message, if there is no existing status message
                 */
                addNewMessage(new Message(true, v[0]));
            }
        } 

And Then

@Override
        protected void onPostExecute(String text) {

            /*
             * check if there is any status message, now remove it.
             */
            if (messages.get(messages.size() - 1).isStatusMessage) {
                messages.remove(messages.size() - 1);
            }
            /*
             * add the orignal message from server.
             */
            addNewMessage(new Message(text, false));
        }

    }

    void addNewMessage(Message m) {
        messages.add(m);
        adapter.notifyDataSetChanged();
        getListView().setSelection(messages.size() - 1);
    }

There is a source code available Simple Android Instant Messaging Application.