Android : Android: ListView is not updating with new data using SimpleAdapter

I am passing the data from my second activity to first activity ListView. When i am passing the data from second Activity to first Activity ListView items is overriding each time. I want to add new item each time. I am using SimpleAdapter. But it is not updating with new items.

Here is my code

         protected void onActivityResult(int requestCode, int resultCode, Intent data) {

        if (requestCode == 1) {
            if(resultCode == RESULT_OK){
                Bundle b = data.getExtras();
                if ( b!= null ){
                String strName=data.getStringExtra("name");
                String strQty=data.getStringExtra("quantity");
                System.out.println(strName);
                System.out.println(strQty);
                List<HashMap<String,String>> aList = new ArrayList<HashMap<String,String>>();


                    HashMap<String, String> hm = new HashMap<String,String>();

                    hm.put("txt", strName);
                    hm.put("cur",strQty);
                    aList.add(hm);

                // Keys used in Hashmap
                String[] from = {"txt","cur" };

                // Ids of views in listview_layout
                int[] to = {R.id.txt,R.id.cur};

                // Instantiating an adapter to store each items
                // R.layout.listview_layout defines the layout of each item
                adapter = new SimpleAdapter(getBaseContext(), aList, R.layout.add_list_detail, from, to);
                listView.setAdapter(adapter);
                adapter.notifyDataSetChanged();

                }
            }
            if (resultCode == RESULT_CANCELED) {
                //Write your code if there's no result
            }
        }
    }

And here is the code from where i am passing the values

          EditText editName = (EditText) findViewById(R.id.txtName);
             EditText editQty=(EditText) findViewById(R.id.txtqty);
             String name= editName.getText().toString();
             String quantity=editQty.getText().toString();
             Intent returnIntent = new Intent();
             returnIntent.putExtra("name",name);
             returnIntent.putExtra("quantity",quantity);
              setResult(RESULT_OK,returnIntent);
             finish();