public class BackgroundWorker extends AsyncTask<String,Void,String> {
 Context context;
 AlertDialog alertDialog;
BackgroundWorker (Context ctx) {
    context = ctx;
}
@Override
protected String doInBackground(String... params) {
    String type = params[0];
    String login_url = "https://prontocars.000webhostapp.com/UserRegistration/login.php";
    if(type.equals("login")) {
        try {
            String username = params[1];
            String password = params[2];
            URL url = new URL(login_url);
            HttpURLConnection httpURLConnection = (HttpURLConnection)url.openConnection();
            httpURLConnection.setRequestMethod("POST");
            httpURLConnection.setDoOutput(true);
            httpURLConnection.setDoInput(true);
            OutputStream outputStream = httpURLConnection.getOutputStream();
            BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8"));
            String post_data = URLEncoder.encode("username","UTF-8")+"="+URLEncoder.encode(username,"UTF-8")+"&"
                    +URLEncoder.encode("password","UTF-8")+"="+URLEncoder.encode(password,"UTF-8");
            bufferedWriter.write(post_data);
            bufferedWriter.flush();
            bufferedWriter.close();
            outputStream.close();
            InputStream inputStream = httpURLConnection.getInputStream();
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream,"iso-8859-1"));
            String result="";
            String line="";
            while((line = bufferedReader.readLine())!= null) {
                result += line;
            }
            bufferedReader.close();
            inputStream.close();
            httpURLConnection.disconnect();
            return result;
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    return null;
}

@Override
protected void onPreExecute() {
    alertDialog = new AlertDialog.Builder(context).create();
    alertDialog.setTitle("Login Status");
}

@Override
protected void onPostExecute(String result) {
    // alertDialog.setMessage(result);
    // alertDialog.show();
    if (result.contentEquals("success")) {
        Intent ltm = new Intent(context, MainActivity.class);
                context.startActivity(ltm);

    } else {
        Toast toast = Toast.makeText(context, "Nombre de usuario o contraseña incorrecta", Toast.LENGTH_SHORT);
        toast.show();
    }
}

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