In this article, we will see how to develop an Android application that sends and receives data from a web server using IntentService. IntentService provides a simple mechanism to execute long lasting operations ( eg : downloading data ) in a background thread.

In this application user is able to select a country from a spinner widget and on selecting the country, corresponding capital name will be fetched from an http web server using IntentService and displayed to the user.

Major steps involved in this application are as follows :

Populate Spinner widget with a String ArrayAdapter

Create an IntentService class ( CapitalService ), which will be invoked when user selects a country from the Spinner widget

Override the method “onHandleIntent()” of the IntentService class to fetch the capital of the selected country from a remote server

Define a BroadcastReceiver class ( CapitalReceiver) in MainActivity, to receive the broadcast message send from the IntentService class

Override the method “onReceive()” of the BroadcastReceiver class to receive data from service and set in TextView of the MainActivity

Register the broadcast receiver in MainActivity with Android’s LocalBroadcastManager

This application is developed in Eclipse 4.2.0 with Android SDK ( 22.2.1 ) and ADT plugin ( 22.2.1 )

1. Create an Android application project with the given below project details

Application Name : IntentServiceDemo

Project Name : IntentServiceDemo

Package Name : in.wptrafficanalyzer.intentservicedemo

Minimum Required SDK : API 8 : Android 2.2 ( Froyo )

Target SDK : API 18 : Android 4.3

Compile With : API 18 : Android 4.3

Theme : Holo Light with Dark Action Bar

2. Update the layout file res/layout/activity_main.xml for the MainActivity

<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" > <Spinner android:id="@+id/spr_country" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerHorizontal="true" /> <TextView android:id="@+id/tv_capital" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_below="@id/spr_country" android:layout_centerHorizontal="true" /> </RelativeLayout>

3. Creating a layout for the Spinner Items in the file res/layout/spinner_layout.xml

<?xml version="1.0" encoding="utf-8"?></pre> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/tv_item" android:padding="15dp" android:textColor="@android:color/black" > </TextView>

4. Creating a class called Constants to define application constants in the file src/in/wptrafficanalyzer/intentservicedemo/Constants.java

package in.wptrafficanalyzer.intentservicedemo; public final class Constants { // Action Name to IntentFilter public static final String BROADCAST_ACTION = "in.wptrafficanalyzer.intentservicedemo.BROADCAST"; public static final String EXTRA_COUNTRY = "country"; public static final String EXTRA_CAPITAL = "capital"; // The url to the server where php script for capital is available public static final String SERVER_URL = "http://wptrafficanalyzer.in/p/intent_service_demo"; }

5. Creating an IntentService class called CapitalService in the file src/in/wptrafficanalyzer/intentservicedemo/CapitalService.java

package in.wptrafficanalyzer.intentservicedemo; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.io.UnsupportedEncodingException; import java.net.HttpURLConnection; import java.net.URL; import java.net.URLEncoder; import android.app.IntentService; import android.content.Intent; import android.support.v4.content.LocalBroadcastManager; import android.util.Log; public class CapitalService extends IntentService{ public CapitalService(){ super("Empty Constructor"); } public CapitalService(String name) { super(name); // TODO Auto-generated constructor stub } // This method is executed in background when this service is started @Override protected void onHandleIntent(Intent intent) { String country = ""; String capital = ""; String url = ""; try { country = URLEncoder.encode(intent.getStringExtra(Constants.EXTRA_COUNTRY),"utf-8"); } catch (UnsupportedEncodingException e1) { // TODO Auto-generated catch block e1.printStackTrace(); } url = Constants.SERVER_URL + "/get_capital.php?country=" + country; try { // Retreiving capital from the url capital = downloadUrl(url); // Creating an intent for broadcastreceiver Intent broadcastIntent = new Intent(Constants.BROADCAST_ACTION); // Attaching data to the intent broadcastIntent.putExtra(Constants.EXTRA_CAPITAL, capital); // Sending the broadcast LocalBroadcastManager.getInstance(getApplicationContext()).sendBroadcast(broadcastIntent); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } /** A method to download data from url */ private String downloadUrl(String strUrl) throws IOException{ String data = ""; InputStream iStream = null; HttpURLConnection urlConnection = null; try{ URL url = new URL(strUrl); // Creating an http connection to communicate with url urlConnection = (HttpURLConnection) url.openConnection(); // Connecting to url urlConnection.connect(); // Reading data from url iStream = urlConnection.getInputStream(); bufferedReader br = new BufferedReader(new InputStreamReader(iStream)); StringBuffer sb = new StringBuffer(); String line = ""; while( ( line = br.readLine()) != null){ sb.append(line); } data = sb.toString(); br.close(); }catch(Exception e){ Log.d("Exception while fetching data", e.toString()); }finally{ iStream.close(); urlConnection.disconnect(); } return data; } }

6. Updating the class MainActivity in the file src/in/wptrafficanalyzer/intentservicedemo/MainActivity.java

package in.wptrafficanalyzer.intentservicedemo; import android.app.Activity; import android.content.BroadcastReceiver; import android.content.Context; import android.content.Intent; import android.content.IntentFilter; import android.os.Bundle; import android.support.v4.content.LocalBroadcastManager; import android.view.Menu; import android.view.View; import android.widget.AdapterView; import android.widget.AdapterView.OnItemSelectedListener; import android.widget.ArrayAdapter; import android.widget.Spinner; import android.widget.TextView; public class MainActivity extends Activity { // Array of countries String[] mCountry = new String[] { "India", "Pakistan", "Bangladesh", "Srilanka", "Nepal", "China", "Japan", "South Korea", "North Korea", "Afghanistan" }; Spinner mSprCountry; TextView mTvCapital; ArrayAdapter<String> mAdapter; Intent mServiceIntent; CapitalReceiver mReceiver; IntentFilter mFilter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); // Adapter for Country Spinner mAdapter = new ArrayAdapter<String>(getApplicationContext(),R.layout.spinner_layout, mCountry); // Getting reference to TextView mTvCapital = (TextView) findViewById(R.id.tv_capital); // Getting reference to Country Spinner mSprCountry = (Spinner) findViewById(R.id.spr_country); // Setting adapter for the Country Spinner mSprCountry.setAdapter(mAdapter); // Creating an intent service mServiceIntent = new Intent(getApplicationContext(), CapitalService.class); mSprCountry.setOnItemSelectedListener(new OnItemSelectedListener() { @Override public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3) { if(arg1!=null){ String country = ((TextView)arg1).getText().toString(); mServiceIntent.putExtra(Constants.EXTRA_COUNTRY, country); // Starting the CapitalService to fetch the capital of the country startService(mServiceIntent); } } @Override public void onNothingSelected(AdapterView<?> arg0) { // TODO Auto-generated method stub } }); // Instantiating BroadcastReceiver mReceiver = new CapitalReceiver(); // Creating an IntentFilter with action mFilter = new IntentFilter(Constants.BROADCAST_ACTION); // Registering BroadcastReceiver with this activity for the intent filter LocalBroadcastManager.getInstance(getApplicationContext()).registerReceiver(mReceiver, mFilter); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.main, menu); return true; } // Defining a BroadcastReceiver private class CapitalReceiver extends BroadcastReceiver{ @Override public void onReceive(Context context, Intent intent) { String capital = intent.getStringExtra(Constants.EXTRA_CAPITAL); mTvCapital.setText("Capital : " + capital); } } }

7. Create a php script file namely “get_capital.php” in a web server having php support

<?php $country = "none"; $capital = array( "India"=>"New Delhi", "Pakistan"=>"Islamabad", "Bangladesh"=>"Dhaka", "Srilanka"=>"Colombo", "Nepal"=>"Kathmandu", "China"=>"Beijing", "Japan"=>"Tokyo", "South Korea"=>"Seoul", "North Korea"=>"Pyongyang", "Afghanistan"=>"Kabul", ); if(isset($_GET['country'])){ $country = $_GET['country']; } if(array_key_exists($country,$capital)) echo $capital[$country]; else echo "Please pass a valid 'country' param from this list : " . implode(",",array_keys($capital));

Note : After creating this file, please ensure that, the variable SERVER_URL of the class Constants is updated with your server url.

8. Screenshot of the application

9. Download the source code of the application

Android Sending and Receiving data from remote server using IntentService 515.71 KB Download Full Source Code

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I am George Mathew, working as software architect and Android app developer at wptrafficanalyzer.in



You can hire me on hourly basis or on project basis for Android applications development.



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