Simple parse JSON from URL on Android and display in listview

Question

I'm trying to parse a JSON result fetched from a URL in my Android app...

I have tried a few examples on the Internet, but can't get it to work. The JSON data looks like this:

[     {         "city_id": "1",         "city_name": "Noida"     },     {         "city_id": "2",         "city_name": "Delhi"     },     {         "city_id": "3",         "city_name": "Gaziyabad"     },     {         "city_id": "4",         "city_name": "Gurgaon"     },     {         "city_id": "5",         "city_name": "Gr. Noida"     } ] 

What's the simplest way to fetch the URL and parse the JSON data show it in the listview

Answer 1

You could use AsyncTask, you'll have to customize to fit your needs, but something like the following

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Async task has three primary methods:

1. onPreExecute() - most commonly used for setting up and starting a progress dialog

2. doInBackground() - Makes connections and receives responses from the server (Do NOT try to assign response values to GUI elements, this is a common mistake, that cannot be done in a background thread).

3. onPostExecute() - Here we are out of the background thread, so we can do user interface manipulation with the response data, or simply assign the response to specific variable types.

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First we will start the class, initialize a String to hold the results outside of the methods but inside the class, then run the onPreExecute() method setting up a simple progress dialog.

class MyAsyncTask extends AsyncTask<String, String, Void> {      private ProgressDialog progressDialog = new ProgressDialog(MainActivity.this);     InputStream inputStream = null;     String result = "";       protected void onPreExecute() {         progressDialog.setMessage("Downloading your data...");         progressDialog.show();         progressDialog.setOnCancelListener(new OnCancelListener() {             public void onCancel(DialogInterface arg0) {                 MyAsyncTask.this.cancel(true);             }         });     } 

Then we need to set up the connection and how we want to handle the response:

    @Override     protected Void doInBackground(String... params) {          String url_select = "http://yoururlhere.com";          ArrayList<NameValuePair> param = new ArrayList<NameValuePair>();          try {             // Set up HTTP post              // HttpClient is more then less deprecated. Need to change to URLConnection             HttpClient httpClient = new DefaultHttpClient();              HttpPost httpPost = new HttpPost(url_select);             httpPost.setEntity(new UrlEncodedFormEntity(param));             HttpResponse httpResponse = httpClient.execute(httpPost);             HttpEntity httpEntity = httpResponse.getEntity();              // Read content & Log             inputStream = httpEntity.getContent();         } catch (UnsupportedEncodingException e1) {             Log.e("UnsupportedEncodingException", e1.toString());             e1.printStackTrace();         } catch (ClientProtocolException e2) {             Log.e("ClientProtocolException", e2.toString());             e2.printStackTrace();         } catch (IllegalStateException e3) {             Log.e("IllegalStateException", e3.toString());             e3.printStackTrace();         } catch (IOException e4) {             Log.e("IOException", e4.toString());             e4.printStackTrace();         }         // Convert response to string using String Builder         try {             BufferedReader bReader = new BufferedReader(new InputStreamReader(inputStream, "utf-8"), 8);             StringBuilder sBuilder = new StringBuilder();              String line = null;             while ((line = bReader.readLine()) != null) {                 sBuilder.append(line + "\n");             }              inputStream.close();             result = sBuilder.toString();          } catch (Exception e) {             Log.e("StringBuilding & BufferedReader", "Error converting result " + e.toString());         }     } // protected Void doInBackground(String... params) 

Lastly, here we will parse the return, in this example it was a JSON Array and then dismiss the dialog:

    protected void onPostExecute(Void v) {         //parse JSON data         try {             JSONArray jArray = new JSONArray(result);                 for(i=0; i < jArray.length(); i++) {                  JSONObject jObject = jArray.getJSONObject(i);                  String name = jObject.getString("name");                 String tab1_text = jObject.getString("tab1_text");                 int active = jObject.getInt("active");              } // End Loop             this.progressDialog.dismiss();         } catch (JSONException e) {             Log.e("JSONException", "Error: " + e.toString());         } // catch (JSONException e)     } // protected void onPostExecute(Void v) } //class MyAsyncTask extends AsyncTask<String, String, Void>