Wednesday, 1 January 2014

Android JSON Parsing Using Async Task

JSON Parsing in Android using Asynctask

In Previous tutorial, mentioned about JSON types and how JSON parsing is happening without using asynctask. In this tutorial, I will talk about JSON parsing using Asynctask.  

What is Async Task?
 AsyncTask enables proper and easy use of the UI thread.This class allows to perform  background operations and publish results on the UI thread.

Async Task has Four Operations:
         1. onPreExecute()- It invoked before execution.
         2. onPostExecute()- It invoked after execution.
         3. doInBackground()- Main operation, write your long operation code.
         4. onPregressUpdate()- It indicates user on progress.

Async Task has Three generic types:

AsyncTask<Param, Progress, Result>
AsyncTask<{Type of Input},{Type of Update Unit},{Type of Update Result}>



In this tutorial, I am taking an example of following JSON which will give you list of News and each “NewsLines” have different Head-Lines and Date-Lines. You can get this JSON by accessing  http://mfeeds.timesofindia.indiatimes.com/Feeds/jsonfeed?newsid=3947071&amp;amp;format=simplejson


If you observe carefully, you can see { and ]. The main difference between these two is object and array. Curly bracket { represents JSONObject and Square bracket [ represents JSONArray.



In this example, I will create a button and after clicking on button the data will show in listview. So our main.xml will be like this:
Activity_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <Button
        android:id="@+id/getdata"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="14dp"
        android:text="Get Data" />

    <ListView
        android:id="@android:id/list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_above="@+id/getdata"
        android:layout_centerHorizontal="true" >

    </ListView>

</RelativeLayout>

Now we will create Parser class. This parser class is used to execute the JSON link and get the JSON data and returns JSON Object.

public class Parser {

    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";
    public JSONObject getJSONData(String url){
            try{
                        DefaultHttpClient client = new DefaultHttpClient();
                        HttpPost post = new HttpPost(url);
                        HttpResponse response = client.execute(post);
                        HttpEntity entity = response.getEntity();
                        is = entity.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 {
            jObj = new JSONObject(json);
        } catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " + e.toString());
        }
        return jObj;
    }
}

In NewsLines, there are multiple strings i.e HeadLine and DateLine. So you need to define these in your MainActivity class.
    private static final String NEWS = "NewsML";
        private static final String NEWS_LINE = "NewsLines";
        private static final String HEAD_LINE = "HeadLine";
        private static final String DATE_LINE = "DateLine";
After button click, it will execute AsyncTask, so you need to write like this way:

Btngetdata.setOnClickListener(new OnClickListener() {
                                   
                                    @Override
                                    public void onClick(View v) {
                                                new JSONParse().execute();
                                    }
                        });


Here JSONParse is a class for Asynctask operation.By using this JSONParse class, it will get the data and fill in the list view. So JSONPasre class will look like this:

private class JSONParse extends AsyncTask<String, Integer, ArrayList<HashMap<String, String>>>{


  
ArrayList<HashMap<String, String>> newsList = new ArrayList<HashMap<String, String>>();

                        
        private ProgressDialog pDialog;
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(MainActivity.this);
            pDialog.setMessage("Loading Data ...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(true);
            pDialog.show();
        }


                        @Override
        protected ArrayList<HashMap<String, String>> doInBackground(String... params) {

             Parser jParser = new Parser();
            JSONObject json = jParser.getJSONData(url);
            try{
                        news = json.getJSONArray(NEWS);
                        for(int i=0;i<news.length();i++){
                                    JSONObject object = news.getJSONObject(i);
                                    JSONObject newsline = object.getJSONObject(NEWS_LINE);
                                    String headLine = newsline.getString(HEAD_LINE);
                                    String dateLine = newsline.getString(DATE_LINE);
                                    HashMap<String, String> map = new HashMap<String, String>();
                                    map.put(HEAD_LINE, headLine);
                                    map.put(DATE_LINE, dateLine);
                                    newsList.add(map);
                        }
            }catch(JSONException e){
                        e.printStackTrace();
            }
            return newsList;
           }//Ending doInBackground


                        @Override
           protected void onPostExecute(ArrayList<HashMap<String, String>> result) {

                                    super.onPostExecute(result);
                                    pDialog.dismiss();
                                    String []from = {HEAD_LINE,DATE_LINE};
                                    int []to = {R.id.tv_headLn,R.id.tv_dateLn};
                                    ListAdapter adapter = new SimpleAdapter(MainActivity.this, result,R.layout.listview_item, from, to);
                                    setListAdapter(adapter);
                        }


So the MainActivity class will look like this:

MainActivity.java

public class MainActivity extends ListActivity {

    Button Btngetdata;
    private static final String NEWS = "NewsML";
    private static final String NEWS_LINE = "NewsLines";
    private static final String HEAD_LINE = "HeadLine";
    private static final String DATE_LINE = "DateLine";
    JSONArray news = null;
    //URL to get JSON Array
    private static String url = "http://mfeeds.timesofindia.indiatimes.com/Feeds/jsonfeed?newsid=3947071&amp;amp;format=simplejson";

            @Override
            protected void onCreate(Bundle savedInstanceState) {
                        super.onCreate(savedInstanceState);
                        requestWindowFeature(Window.FEATURE_NO_TITLE);
                        setContentView(R.layout.activity_main);
                        Btngetdata = (Button)findViewById(R.id.getdata);
                        Btngetdata.setOnClickListener(new OnClickListener() {
                                   
                                    @Override
                                    public void onClick(View v) {
                                                new JSONParse().execute();
                                    }
                        });
            }

        private class JSONParse extends AsyncTask<String, Integer, ArrayList<HashMap<String, String>>>{

ArrayList<HashMap<String, String>> newsList = new ArrayList<HashMap<String, String>>();


            private ProgressDialog pDialog;

            protected void onPreExecute() {

            super.onPreExecute();
            pDialog = new ProgressDialog(MainActivity.this);
            pDialog.setMessage("Loading Data ...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(true);
            pDialog.show();
        }

                        @Override
        protected ArrayList<HashMap<String, String>> doInBackground(String... params) {

             Parser jParser = new Parser();
            JSONObject json = jParser.getJSONData(url);
            try{
                        news = json.getJSONArray(NEWS);
                        for(int i=0;i<news.length();i++){
                                    JSONObject object = news.getJSONObject(i);
                                    JSONObject newsline = object.getJSONObject(NEWS_LINE);
                                    String headLine = newsline.getString(HEAD_LINE);
                                    String dateLine = newsline.getString(DATE_LINE);
                                    HashMap<String, String> map = new HashMap<String, String>();
                                    map.put(HEAD_LINE, headLine);
                                    map.put(DATE_LINE, dateLine);
                                    newsList.add(map);
                        }
            }catch(JSONException e){
                        e.printStackTrace();
            }
            return newsList;
         }
                        @Override
        protected void onPostExecute(ArrayList<HashMap<String, String>> result) {

                                    
                                    super.onPostExecute(result);
                                    pDialog.dismiss();
                                    String []from = {HEAD_LINE,DATE_LINE};
                                    int []to = {R.id.tv_headLn,R.id.tv_dateLn};
                                    ListAdapter adapter = new SimpleAdapter(MainActivity.this, result, R.layout.listview_item, from, to);
                                    setListAdapter(adapter);

                        }
                       
            }
}

Result:













11 comments:

  1. De donde sacas R.id.tv_headLn , R.id.tv_dateLn ?

    Gracias

    ReplyDelete
  2. Sorry I meant, where did you get R.id.tv_headLn , R.id.tv_dateLn ?

    ReplyDelete
  3. very nicely elucidated

    ReplyDelete
  4. I read this article got very useful and understandable for me through step by step description thanks for sharing.
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    ReplyDelete
  5. i am having warning that DefaultHttpClient is the deprecated code

    ReplyDelete
  6. madhavi laddha

    ReplyDelete
  7. • Nice and good article. It is very useful for me to learn and understand easily. Thanks for sharing your valuable information and time. Please keep updatingAzure Online Training

    ReplyDelete