Question

Background : I am trying to develop my first android application which is a student discussion panel. I am good with PHP and MySQL but don’t have much experience in android Java.

Issue:
In SelectedQuestionActivity class, if I simply give the URL as http://thewbs.getfreehosting.co.uk/talky/fetchans.php?qid=3, it works just fine and it fetches the corresponding answer to the question.
But if I do it the way I have shown in the code below, the application crashes. I am not sure where I am wrong.

CODE:
AllQuestionActivity.java

         public void onItemClick(AdapterView<?> parent, View view,
                int position, long id) {
            // getting values from selected ListItem
            String pid = ((TextView) view.findViewById(R.id.qid)).getText()
                    .toString();
             //pid is the value of the selected question for example www.example.com/fetchans?qid=3 so here pid value is supposed to be 3. 
            // Starting new intent
            Intent in = new Intent(getApplicationContext(),
                    SelectedQuestionActivity.class);
            // sending pid to next activity
            in.putExtra(TAG_PID, pid);
            startActivity(in);

        }
    });

Now in SelectedQuestionActivity.java
code:

public class SelectedQuestionActivity extends ListActivity {

// Progress Dialog
private ProgressDialog pDialog;

// Creating JSON Parser object
JSONParser jParser = new JSONParser();

ArrayList<HashMap<String, String>> productsList;

Intent intent = getIntent();
String qid = intent.getExtras().getString(TAG_PID);
// url to get all products list
private String url_all_products = "http://thewbs.getfreehosting.co.uk/talky/fetchans.php?qid="+qid;

// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_PRODUCTS = "ques";
private static final String TAG_PID = "aid";
private static final String TAG_NAME = "aname";
private static final String TAG_INFO = "answer";
private static final String TAG_DATE = "date";
// products JSONArray
JSONArray products = null;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.all_ans);

    // Hashmap for ListView
    productsList = new ArrayList<HashMap<String, String>>();

    // Loading products in Background Thread
    new LoadAllProducts().execute();

    // Get listview
    ListView lv = getListView();
 }
  class LoadAllProducts extends AsyncTask<String, String, String> {

    /**
     * Before starting background thread Show Progress Dialog
     * */
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = new ProgressDialog(SelectedQuestionActivity.this);
        pDialog.setMessage("Loading Answers. Please wait...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(false);
        pDialog.show();
    }

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

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

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

            if (success == 1) {
                // products found
                products = json.getJSONArray(TAG_PRODUCTS);

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

                    // Storing each json item in variable
                    String id = c.getString(TAG_PID);
                    String name = c.getString(TAG_NAME);
                    String info = c.getString(TAG_INFO);
                    String date = c.getString(TAG_DATE);
                    // creating new HashMap
                    HashMap<String, String> map = new HashMap<String, String>();

                    // adding each child node to HashMap key => value
                    map.put(TAG_PID, id);
                    map.put(TAG_NAME, name);
                    map.put(TAG_INFO, info);
                    map.put(TAG_DATE, date);

                    // adding HashList to ArrayList
                    productsList.add(map);
                }
            } 
            else {

            }
        } 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
        runOnUiThread(new Runnable() {
            public void run() {
                /**
                 * Updating parsed JSON data into ListView
                 * */
                ListAdapter adapter = new SimpleAdapter(
                        SelectedQuestionActivity.this, productsList,
                        R.layout.list_selected_ques, new String[] { TAG_PID,
                                TAG_NAME, TAG_INFO, TAG_DATE },
                        new int[] { R.id.aid, R.id.aname, R.id.answer, R.id.date});
                // updating listview
                setListAdapter(adapter);
            }
        });

    }

   }
  }

JSONparser.java

public class JSONParser {

static InputStream is = null;
static JSONObject jObj = null;
static String json = "";

// constructor
public JSONParser() {

}

// function get json from url
// by making HTTP POST or GET method
public JSONObject makeHttpRequest(String url, String method,
        List<NameValuePair> params) {

    // Making HTTP request
    try {

        // check for request method
        if(method == "POST"){
            // request method is POST
            // defaultHttpClient
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);
            httpPost.setEntity(new UrlEncodedFormEntity(params));

            HttpResponse httpResponse = httpClient.execute(httpPost);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();

        }else if(method == "GET"){
            // request method is GET
            DefaultHttpClient httpClient = new DefaultHttpClient();
            String paramString = URLEncodedUtils.format(params, "utf-8");
            url += "?" + paramString;
            HttpGet httpGet = new HttpGet(url);

            HttpResponse httpResponse = httpClient.execute(httpGet);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();
        }           

    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "iso-8859-1"), 8);
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
        is.close();
        json = sb.toString();
    } catch (Exception e) {
        Log.e("Buffer Error", "Error converting result " + e.toString());
    }

    // try parse the string to a JSON object
    try {
        jObj = new JSONObject(json);
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }

    // return JSON String
    return jObj;

}
}

Answer 1

Currently you are trying to getIntent outside onCreate of ListActivity so move it inside onCreate method as :

 Intent intent;
String qid;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.all_ans);

       // get Intent here 
      intent = getIntent();
      qid = intent.getExtras().getString(TAG_PID);

       // your code here

and also no need to use runOnUiThread method for updating UI from onPostExecute because onPostExecute method called on Ui thread we can access UI elements in it

EDIT:-

you are not adding any paramter to NameValuePair inside doInBackground . add quid before sending it to makeHttpRequest as :

 protected String doInBackground(String... args) {
 // Building Parameters
List<NameValuePair> params = new ArrayList<NameValuePair>();
add quid param here
params.add(new BasicNameValuePair("qid",qid));  //<<<< add here
// getting JSON string from URL
JSONObject json = jParser.makeHttpRequest(
                      url_all_products,
                      "GET", 
                      params);
// your code here