Question

I have a ListView with a SimpleAdapter. The Data for the ListView comes from json. I want to update the ListView every 5 min.
That works fine… But the ListView is allway a double. All items are to times in the ListView. Why? And wenn I update then 3 times….
I try

setListAdapter(null);

and

mylist.clear();

no effect

public class StartActivity extends ListActivity {
    TextView text_1,text_2 ;
    private Timer autoUpdate;
    ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>();
    Button btnShowLocation;

    // GPSTracker class
    GpsData gps;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.listplaceholder);

        btnShowLocation = (Button) findViewById(R.id.report_btn);

        // show location button click event
        btnShowLocation.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                Intent intent = new Intent(StartActivity.this, ReportActivity.class);
                startActivity(intent);

            }
        });

        new task().execute();
    }

     @Override
     public void onResume() {
      super.onResume();
      autoUpdate = new Timer();
      autoUpdate.schedule(new TimerTask() {
       @Override
       public void run() {
        runOnUiThread(new Runnable() {
         public void run() {
             new task().execute();
         }
        });
       }
      }, 0, 300000); // updates each 5 min
     }

class task extends AsyncTask<String, String, Void>
{
private ProgressDialog progressDialog = new ProgressDialog(StartActivity.this);
    InputStream is = null ;
    String result = "";
    protected void onPreExecute() {
       progressDialog.setMessage("Status Update...");
       progressDialog.show();
       progressDialog.setOnCancelListener(new OnCancelListener() {
    @Override
        public void onCancel(DialogInterface arg0) {
        task.this.cancel(true);
       }
    });
     }
       @Override
    protected Void doInBackground(String... params) {
           //mylist.clear();


           JSONObject json = jsonFunctions.getJSONfromURL("http://my.de", mlat, mlon);

      try{
        //String text = getString(R.string.report_TJ);
        JSONArray  earthquakes = json.getJSONArray("uTraf");

            for(int i=0;i<earthquakes.length();i++){                        
                HashMap<String, String> map = new HashMap<String, String>();    
                JSONObject e = earthquakes.getJSONObject(i);

                map.put("id",  String.valueOf(i));
                map.put("first", "Stau: " + e.getString("road") + ", " + e.getString("county"));
                map.put("second", e.getString("timestamp") + ", " + e.getString("suburb"));
                mylist.add(map);            
            }       
      }catch(JSONException e)        {
         Log.e("log_tag", "Error parsing data "+e.toString());
      }

            return null;

        }
    protected void onPostExecute(Void v) {
        //setListAdapter(null);
        ListAdapter adapter = new SimpleAdapter(StartActivity.this, mylist , R.layout.main, 
                new String[] { "first", "second" }, 
                new int[] { R.id.item_title, R.id.item_subtitle });

setListAdapter(adapter);

final ListView lv = getListView();
lv.setTextFilterEnabled(true);  
lv.setOnItemClickListener(new OnItemClickListener() {
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {              
        @SuppressWarnings("unchecked")
        HashMap<String, String> o = (HashMap<String, String>) lv.getItemAtPosition(position);                   
        Toast.makeText(StartActivity.this, "ID '" + o.get("id") + "' was clicked.", Toast.LENGTH_SHORT).show(); 

    }
});
            this.progressDialog.dismiss();

        } 
    }


@Override
public void onPause() {
 autoUpdate.cancel();
 super.onPause();
}


}

Answer 1

Your problem is with the call mylist.add(map); inside your for loop in doInBackground.

Your creating a map is fine but by calling the add function on mylist you are appending it to the list and not overriding the current map with the same keys. If you want to update existing items in the listview as opposed to just overwriting with fresh data then the mylist variable should probably be a HashMap also.

EDIT – Solution:

In doInBackground, just before you enter the loop to process data

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

call mylist.clear(). This will empty your array list before you start to add new data to it.