android - 如何清除ListView中的数据？异步任务

Question

我在 fragment 中有以下 AsyncTask，我想清除 ListView 并在单击按钮时重新填充它。这是我尝试过的:

按钮点击:

btnRefresh.setOnClickListener(new View.OnClickListener() {
    @Override
public void onClick(View view) {
    lv.setAdapter(null);
        new LoadAllProducts().execute();
}
});

这是我的 AsyncTask:

class LoadAllProducts extends AsyncTask<String, String, String> {

    //ListView lv = (ListView) rootView.findViewById(R.id.list);
    /**
     * Before starting background thread Show Progress Dialog
     * */
    @Override
    protected void onPreExecute() {
        super.onPreExecute();

        lv.setAdapter(null);
        pDialog = new ProgressDialog(getActivity());
        pDialog.setMessage("Loading your trips. Please wait...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(false);
        pDialog.show();
    }

    /**
     * getting All products from url
     * */
    protected String doInBackground(String... args) {
        // Building Parameters
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        // getting JSON string from URL
        JSONObject json = jParser.makeHttpRequest(url_all_trips, "GET", params);

        // Check your log cat for JSON response
        Log.d("All Trips: ", json.toString());

        try {
            // Checking for SUCCESS TAG
            int success = json.getInt(TAG_SUCCESS);

            if (success == 1) {
                // products found
                // Getting Array of Products
                trips = json.getJSONArray(TAG_TRIPS);

                // looping through All Products
                for (int i = 0; i < trips.length(); i++) {
                    JSONObject c = trips.getJSONObject(i);

                    // Storing each json item in variable
                    String tripid = c.getString(TAG_TRIPID);
                    String tripname = c.getString(TAG_TRIPNAME);
                    String userId = c.getString("uid");

                    // creating new HashMap
                    DatabaseHandler_Helpers db = new DatabaseHandler_Helpers(getActivity());
                    HashMap<String, String> map = new HashMap<String, String>();

                    if (userId.equals(db.getUserDetails().get("uid"))) {
                        // adding each child node to HashMap key => value
                        map.put(TAG_TRIPID, tripid);
                        map.put(TAG_TRIPNAME, tripname);

                        // adding HashList to ArrayList
                        tripList.add(map);
                    } //else {
                        //map.put(TAG_TRIPID, "");
                        //map.put(TAG_TRIPNAME, "You have no tracked trips.");

                        //tripList.add(map);
                    //}
                }
            } else {
                // no products found
                // Launch Add New product Activity
                Intent i = new Intent(getActivity(),
                        NewTrip_Activity.class);
                // Closing all previous activities
                i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(i);
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }

        return null;
    }

    /**
     * After completing background task Dismiss the progress dialog
     * **/
    protected void onPostExecute(String file_url) {
        // dismiss the dialog after getting all products
        pDialog.dismiss();

        // updating UI from Background Thread
        ((Activity) getActivity()).runOnUiThread(new Runnable() {
            public void run() {
                /**
                 * Updating parsed JSON data into ListView
                 * */


                ListAdapter adapter = new SimpleAdapter(
                        getActivity(), tripList,
                        R.layout.list_item, new String[] { TAG_TRIPID,
                                TAG_TRIPNAME, "TEST"},
                        new int[] { R.id.pid, R.id.name, R.id.mileage });
                // updating listview
                ((ListView) lv.findViewById(R.id.list)).setAdapter(adapter);
            }
        });
     }
 }

问题是单击按钮会清除 ListView ，但随后会将项目添加两次。因此， ListView 中已经存在的内容再次加上相同的项目。如果您再次单击该按钮，它会第三次添加项目!

我知道我一定遗漏了一些东西，但我在网上找到的只是使用 ArrayAdapter 而不是 ListAdapter。感谢您帮助解决这个问题!

Answer 1

在将 map 添加到它们之前，您需要清除 tripList.clear() 您的 tripList(arraylist) tripList.add(map) 否则它将添加到现有的旧值