How to use AsyncTask in Android application

Issue

I'm developing an application for android, my problem is the implementation of AsyncTask, what i must do is "simple":

This part of function is used to get information from a database, after data loading, the informations are showed in a table, I would implement a function that allows me to show a progress bar during the retrieval of information (read server)

try {
    String url_img = null;
    String path = "MY FANTASTIC PATH";

    /*READSERVER RETURN JSON STRING THAT CONTAIN SOME IMFORMATION*/

    ReadServer read = new ReadServer();
    String result = read.readserver("list_news","homepage");

    TableLayout MainTable = (TableLayout)findViewById(R.id.main_table); 
    JSONArray Jobj = new JSONArray(result);

    for (int i = 0; i < Jobj.length(); i++){
     TableRow row = new TableRow(getApplicationContext()); 
     row.setLayoutParams(new TableRow.LayoutParams(TableRow.LayoutParams.MATCH_PARENT, TableRow.LayoutParams.WRAP_CONTENT));
     row.setPadding(0, 14, 2, 14);

     JSONObject news_preview = Jobj.getJSONObject(i);
     Integer news_id = news_preview.getInt("id_articolo");
     String news_title = news_preview.getString("titolo");
     String news_image = news_preview.getString("immagine");



     //Check if image url is relative or absolute 
     Pattern p = Pattern.compile("^(https?|ftp|file)://[-a-zA-Z0-9+&@#/%?=~_|!:,.;]*[-a-zA-Z0-9+&@#/%=~_|]");
     Matcher m = p.matcher(news_image);

     if(m.matches() == false){
       url_img = path+news_image;
     }else if(m.matches() == true){
       url_img = news_image;
     }

     //Call Html Parser to parse text
     HtmlParser parsed_string = new HtmlParser();
     Spanned title_nohtml = parsed_string.htmlparser(news_title);

     //Thumb
     ImageView img = new ImageView(getApplicationContext());
     img.setAdjustViewBounds(true);
     img.setMaxHeight(140); img.setMaxWidth(140);
     Bitmap bitmap = BitmapFactory.decodeStream((InputStream)new URL(url_img).getContent());
     img.setImageBitmap(bitmap);

     LayoutParams params =  new TableRow.LayoutParams(
     LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);

     //Clickable title
     final TextView txt = new TextView(getApplicationContext()); 
     txt.setGravity(Gravity.LEFT | Gravity.CENTER_HORIZONTAL | Gravity.CENTER_VERTICAL );
     txt.setLayoutParams(params); txt.setTextSize(18); txt.setBackgroundColor(Color.WHITE);
     txt.setTypeface(null, Typeface.BOLD); txt.setTextColor(Color.BLACK);
     txt.setId(news_id); txt.setText(title_nohtml); txt.setClickable(true);

     row.addView(img);
     row.addView(txt);  
     MainTable.addView(row);

     txt.setOnClickListener(new OnClickListener(){
      public void onClick(View v) {
       Intent intent = new Intent(MainActivity.this, OtherPages.class);
       Bundle extras = new Bundle();
       extras.putString("Boolean","1");
       extras.putInt("id_news", txt.getId());
       intent.putExtras(extras);
       startActivity(intent);
      }
     });
    }    
   }catch(Exception e){
     AlertDialog.Builder alertDialog = new AlertDialog.Builder(this);
     alertDialog.setTitle("Si è verificato un errore");
     alertDialog.setMessage("Errore 001" +"\n"+"Non è stato possibile soddisfare la tua richiesta, riprova più tardi.");
     alertDialog.show();        
   }
  }else{
      connectivityMessage("Nessuna connessione presente, assicurati di avere il traffico dati oppure il Wi-Fi attivato e riprova."); 
  }

I know that i must use this code but i dont know how implements, can anyone help me ?

GetNews getNewsTask = new GetNews().execute();
 private class GetNews extends AsyncTask<Void, Void, Void>{
  private ProgressDialog progress = null;

       @Override
       protected Void doInBackground(Void... params) {

        // do something

        return null;
       }

       @Override
       protected void onCancelled() {
        super.onCancelled();
       }

       @Override
       protected void onPreExecute() {
        progress = ProgressDialog.show(
        MainActivity.this, null, "Caricamento notizie...");
        super.onPreExecute();
      }

       @Override
       protected void onPostExecute(Void result) {
        progress.dismiss();
        super.onPostExecute(result);
      }

       @Override
       protected void onProgressUpdate(Void... values) {
        super.onProgressUpdate(values);
       }
      }

FINAL SOLUTION:

 private class GetNews extends AsyncTask<Void, Void, String>{
  private ProgressDialog progress = null;

   @Override
   protected String doInBackground(Void... params) {
    Looper.prepare(); //MUST BE ADDED
    ReadServer read = new ReadServer();
    String result = read.readserver("list_news","homepage");
    System.out.println("DEBUG"+result);
    return result;
   }

   @Override
   protected void onCancelled() {
    super.onCancelled();
   }

   @Override
   protected void onPreExecute() {
    progress = ProgressDialog.show(
    MainActivity.this, null, "Caricamento notizie");
    super.onPreExecute();
  }

    @Override
    protected void onPostExecute(String result) {
    super.onPostExecute(result);
    try {
     String url_img = null;
     String path = "http://www.MYFANTASTICPATH.it";

     TableLayout MainTable = (TableLayout) findViewById(R.id.main_table);
     JSONArray Jobj = new JSONArray(result);

     for (int i = 0; i < Jobj.length(); i++) {
     TableRow row = new TableRow(getApplicationContext());
     row.setLayoutParams(new TableRow.LayoutParams(TableRow.LayoutParams.MATCH_PARENT, TableRow.LayoutParams.WRAP_CONTENT));
     row.setPadding(0, 14, 2, 14);

     JSONObject news_preview = Jobj.getJSONObject(i);
     Integer news_id = news_preview.getInt("id_articolo");
     String news_title = news_preview.getString("titolo");
     String news_image = news_preview.getString("immagine");

     // Check if image url is relative or absolute
     Pattern p = Pattern.compile("^(https?|ftp|file)://[-a-zA-Z0-9+&@#/%?=~_|!:,.;]*[-a-zA-Z0-9+&@#/%=~_|]");
     Matcher m = p.matcher(news_image);

     if (m.matches() == false) {
         url_img = path + news_image;
     } else if (m.matches() == true) {
        url_img = news_image;
     }

     // Call Html Parser to parse text
     HtmlParser parsed_string = new HtmlParser();
     Spanned title_nohtml = parsed_string.htmlparser(news_title);

     // Thumb
     ImageView img = new ImageView(getApplicationContext());
     img.setAdjustViewBounds(true);
     img.setMaxHeight(140);
     img.setMaxWidth(140);
     Bitmap bitmap = BitmapFactory.decodeStream((InputStream) new URL(url_img).getContent());
     img.setImageBitmap(bitmap);

     LayoutParams params = new TableRow.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);

     // Clickable title
     final TextView txt = new TextView(getApplicationContext());
     txt.setGravity(Gravity.LEFT | Gravity.CENTER_HORIZONTAL | Gravity.CENTER_VERTICAL);
     txt.setLayoutParams(params);
     txt.setTextSize(18);
     txt.setBackgroundColor(Color.WHITE);
     txt.setTypeface(null, Typeface.BOLD);
     txt.setTextColor(Color.BLACK);
     txt.setId(news_id);
     txt.setText(title_nohtml);
     txt.setClickable(true);

     row.addView(img);
     row.addView(txt);
     MainTable.addView(row);

     txt.setOnClickListener(new OnClickListener() {
      public void onClick(View v) {
       Intent intent = new Intent(MainActivity.this, OtherPages.class);
       Bundle extras = new Bundle();
       extras.putString("Boolean", "1");
       extras.putInt("id_news", txt.getId());
       intent.putExtras(extras);
       startActivity(intent);
      }
     });
    }
   }catch (Exception e) {
     AlertDialog.Builder alertDialog = new AlertDialog.Builder(MainActivity.this);
     alertDialog.setTitle("Si è verificato un errore");
     alertDialog.setMessage("Errore 001" + "\n" + "Non è stato possibile soddisfare la tua richiesta, riprova più tardi.");
     alertDialog.show();
    }
    progress.dismiss();
   }

   @Override
    protected void onProgressUpdate(Void... values) {
     super.onProgressUpdate(values);
    }
   }

Solution

ondoInbackground you want to do all the main tasks in the background ....

onPostexecute you display all the results from the doinbackground

P.S : If u want to access to UI,do it in onPostexecute or onProgressupdate

Answered By - Sukan