There are several way for
an Activity
to communicate with an Service and vice versa.

For an introduction into
BroadcastReceiver
please see

Android BroadcastReceiver tutorial

.

A PendingIntent is a token
that you give to another application (e.g. Notification Manager, Alarm Manager
or other 3rd party applications), which allows this other application to use
the permissions of your application to execute a predefined piece of code.

To perform a broadcast via
a pending intent so get a PendingIntent viaPendingIntent.getBroadcast().
To perform an activity via an pending intent you receive the activity via
PendingIntent.getActivity().

The following will demonstrate
how to use the
IntentService
class to download a file from the Internet. Once done the
IntentService
will use an instance of the
Messenger
class to inform the
Activitywhich started the
service about the location of the downloaded file.

Create a new project called
"de.vogella.android.intentservice.download" with a
Activity
calledMainActivity.

Create a service "DownloadService"
by creating the following class and the entry inAndroidManifest.xml.
Also add the permission to write to external storage and to access the Internet
to the file.

package de.vogella.android.intentservice.download;



import java.io.File;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.net.URL;



import android.app.Activity;

import android.app.IntentService;

import android.content.Intent;

import android.net.Uri;

import android.os.Bundle;

import android.os.Environment;

import android.os.Message;

import android.os.Messenger;

import android.util.Log;



public class DownloadService extends IntentService {



  private int result = Activity.RESULT_CANCELED;



  public DownloadService() {

    super("DownloadService");

  }



  // Will be called asynchronously be Android

  @Override

  protected void onHandleIntent(Intent intent) {

    Uri data = intent.getData();

    String urlPath = intent.getStringExtra("urlpath");

    String fileName = data.getLastPathSegment();

    File output = new File(Environment.getExternalStorageDirectory(),

        fileName);

    if (output.exists()) {

      output.delete();

    }



    InputStream stream = null;

    FileOutputStream fos = null;

    try {



      URL url = new URL(urlPath);

      stream = url.openConnection().getInputStream();

      InputStreamReader reader = new InputStreamReader(stream);

      fos = new FileOutputStream(output.getPath());

      int next = -1;

      while ((next = reader.read()) != -1) {

        fos.write(next);

      }

      // Sucessful finished

      result = Activity.RESULT_OK;



    } catch (Exception e) {

      e.printStackTrace();

    } finally {

      if (stream != null) {

        try {

          stream.close();

        } catch (IOException e) {

          e.printStackTrace();

        }

      }

      if (fos != null) {

        try {

          fos.close();

        } catch (IOException e) {

          e.printStackTrace();

        }

      }

    }



    Bundle extras = intent.getExtras();

    if (extras != null) {

      Messenger messenger = (Messenger) extras.get("MESSENGER");

      Message msg = Message.obtain();

      msg.arg1 = result;

      msg.obj = output.getAbsolutePath();

      try {

        messenger.send(msg);

      } catch (android.os.RemoteException e1) {

        Log.w(getClass().getName(), "Exception sending message", e1);

      }



    }

  }

} 

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="de.vogella.android.intentservice.download"

    android:versionCode="1"

    android:versionName="1.0" >



    <uses-sdk android:minSdkVersion="15" />

    <uses-permission android:name="android.permission.INTERNET"/>

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>



    <application

        android:icon="@drawable/ic_launcher"

        android:label="@string/app_name" >

        <activity

            android:name=".MainActivity"

            android:label="@string/app_name" >

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />



                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>



        <service android:name="DownloadService" >

        </service>

    </application>



</manifest> 

Change the
main.xml
layout to the following.

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical" >



    <Button

        android:id="@+id/button1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:onClick="onClick"

        android:text="Button" />



</LinearLayout> 

Change
MainActivity
to the following.

package de.vogella.android.intentservice.download;



import android.app.Activity;

import android.content.Intent;

import android.net.Uri;

import android.os.Bundle;

import android.os.Handler;

import android.os.Message;

import android.os.Messenger;

import android.view.View;

import android.widget.Toast;



public class MainActivity extends Activity {

  private Handler handler = new Handler() {

    public void handleMessage(Message message) {

      Object path = message.obj;

      if (message.arg1 == RESULT_OK && path != null) {

        Toast.makeText(MainActivity.this,

            "Downloaded" + path.toString(), Toast.LENGTH_LONG)

            .show();

      } else {

        Toast.makeText(MainActivity.this, "Download failed.",

            Toast.LENGTH_LONG).show();

      }



    };

  };



  @Override

  public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.main);



  }



  public void onClick(View view) {

    Intent intent = new Intent(this, DownloadService.class);

    // Create a new Messenger for the communication back

    Messenger messenger = new Messenger(handler);

    intent.putExtra("MESSENGER", messenger);

    intent.setData(Uri.parse("http://www.vogella.com/index.html"));

    intent.putExtra("urlpath", "http://www.vogella.com/index.html");

    startService(intent);

  }

} 

If you run your example and
press the button, the download should be performed by the
Service
and once done the
Activity
should show a Toast with the file name.

The following chapter will
demonstrate how to create and consume a service from an activity. The service
will be started at boot and periodically fetch data. The service will used by
an
activity
which bind itself to the service. The activity will allow to request
the latest data from the service.

Create a new project called
de.vogella.android.ownservice.local
with an
Activity
called
MainActivity.

Create the
LocalWordService
class.

package de.vogella.android.ownservice.local;



import java.util.ArrayList;

import java.util.List;

import java.util.Random;



import android.app.Service;

import android.content.Intent;

import android.os.Binder;

import android.os.IBinder;



public class LocalWordService extends Service {

  private final IBinder mBinder = new MyBinder();

  private ArrayList<String> list = new ArrayList<String>();



  @Override

  public int onStartCommand(Intent intent, int flags, int startId) {



    Random random = new Random();

    if (random.nextBoolean()) {

      list.add("Linux");

    }

    if (random.nextBoolean()) {

      list.add("Android");

    }

    if (random.nextBoolean()) {

      list.add("iPhone");

    }

    if (random.nextBoolean()) {

      list.add("Windows7");

    }

    if (list.size() >= 20) {

      list.remove(0);

    }

    return Service.START_NOT_STICKY;

  }



  @Override

  public IBinder onBind(Intent arg0) {

    return mBinder;

  }



  public class MyBinder extends Binder {

    LocalWordService getService() {

      return LocalWordService.this;

    }

  }



  public List<String> getWordList() {

    return list;

  }



} 

Create the following two classes,
which will be registered as
BroadcastReceivers.

package de.vogella.android.ownservice.local;



import java.util.Calendar;



import android.app.AlarmManager;

import android.app.PendingIntent;

import android.content.BroadcastReceiver;

import android.content.Context;

import android.content.Intent;



public class MyScheduleReceiver extends BroadcastReceiver {



  // Restart service every 30 seconds

  private static final long REPEAT_TIME = 1000 * 30;



  @Override

  public void onReceive(Context context, Intent intent) {

    AlarmManager service = (AlarmManager) context

        .getSystemService(Context.ALARM_SERVICE);

    Intent i = new Intent(context, MyStartServiceReceiver.class);

    PendingIntent pending = PendingIntent.getBroadcast(context, 0, i,

        PendingIntent.FLAG_CANCEL_CURRENT);

    Calendar cal = Calendar.getInstance();

    // Start 30 seconds after boot completed

    cal.add(Calendar.SECOND, 30);

    //

    // Fetch every 30 seconds

    // InexactRepeating allows Android to optimize the energy consumption

    service.setInexactRepeating(AlarmManager.RTC_WAKEUP,

        cal.getTimeInMillis(), REPEAT_TIME, pending);



    // service.setRepeating(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis(),

    // REPEAT_TIME, pending);



  }

} 

package de.vogella.android.ownservice.local;



import android.content.BroadcastReceiver;

import android.content.Context;

import android.content.Intent;



public class MyStartServiceReceiver extends BroadcastReceiver {



  @Override

  public void onReceive(Context context, Intent intent) {

    Intent service = new Intent(context, LocalWordService.class);

    context.startService(service);

  }

} 

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="de.vogella.android.ownservice.local"

    android:versionCode="1"

    android:versionName="1.0" >



    <uses-sdk android:minSdkVersion="10" />



    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />



    <application

        android:icon="@drawable/icon"

        android:label="@string/app_name" >

        <activity

            android:name=".MainActivity"

            android:label="@string/app_name" >

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />



                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>



        <service

            android:name=".LocalWordService"

            android:icon="@drawable/icon"

            android:label="@string/service_name" >

        </service>



        <receiver android:name="MyScheduleReceiver" >

            <intent-filter>

                <action android:name="android.intent.action.BOOT_COMPLETED" />

            </intent-filter>

        </receiver>

        <receiver android:name="MyStartServiceReceiver" >

        </receiver>

    </application>



</manifest> 

Change the
main.xml
layout to the following.

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical" >



    <TextView

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:text="@string/hello" />



    <Button

        android:id="@+id/button1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:onClick="showServiceData"

        android:text="Button" >

    </Button>



    <ListView

        android:id="@id/android:list"

        android:layout_width="match_parent"

        android:layout_height="wrap_content" >

    </ListView>



</LinearLayout> 

Change your
Activity
to the following.

package de.vogella.android.ownservice.local;



import java.util.ArrayList;

import java.util.List;



import android.app.ListActivity;

import android.content.ComponentName;

import android.content.Context;

import android.content.Intent;

import android.content.ServiceConnection;

import android.os.Bundle;

import android.os.IBinder;

import android.view.View;

import android.widget.ArrayAdapter;

import android.widget.Toast;



public class MainActivity extends ListActivity {

  private LocalWordService s;



  

@Override

public

void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState); setContentView(R.layout.main); wordList
=

new ArrayList<String>(); adapter =

new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, android.R.id.text1,
wordList); setListAdapter(adapter); doBindService(); }

private ServiceConnection mConnection =

new ServiceConnection() {

public

void onServiceConnected(ComponentName className, IBinder binder) { s
= ((LocalWordService.MyBinder) binder).getService(); Toast.makeText(MainActivity.this,
"Connected", Toast.LENGTH_SHORT).show();
}

public

void onServiceDisconnected(ComponentName className) { s = null; } };

private ArrayAdapter<String> adapter;

private List<String> wordList;

void doBindService() { bindService(new
Intent(this,
LocalWordService.class),
mConnection, Context.BIND_AUTO_CREATE); }

public

void showServiceData(View view) {

if (s != null) { Toast.makeText(this,
"Number of elements" + s.getWordList().size(),
Toast.LENGTH_SHORT).show(); wordList.clear(); wordList.addAll(s.getWordList());
adapter.notifyDataSetChanged(); } } }

The following chapter will
demonstrate how to communicate between an
Activity
and an
Serviceusing the
Messenger
and
Handler
class.

Create a new project called
"de.vogella.android.ownservice.messenger" with an
Activity
calledMainActivity.

Creating the following
AndroidManifest.xml.

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="de.vogella.android.ownservice.messenger"

    android:versionCode="1"

    android:versionName="1.0" >



    <uses-sdk android:minSdkVersion="15" />

    <uses-permission android:name="android.permission.INTERNET"/>

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>



    <application

        android:icon="@drawable/ic_launcher"

        android:label="@string/app_name" >

        <activity

            android:name=".MainActivity"

            android:label="@string/app_name" >

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />



                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>



        <service android:name="DownloadServiceMessenger" >

        </service>

    </application>



</manifest> 

Create the following class

package de.vogella.android.ownservice.messenger;



import java.io.File;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.net.URL;



import android.app.Activity;

import android.app.Service;

import android.content.Intent;

import android.os.Bundle;

import android.os.Environment;

import android.os.Handler;

import android.os.IBinder;

import android.os.Message;

import android.os.Messenger;

import android.os.StrictMode;

import android.util.Log;



public class DownloadServiceMessenger extends Service {

  public static final String FILENAME = "fileName";

  public static final String URLPATH = "urlPath";

  public static final String RESULTPATH = "urlPath";

  private int result = Activity.RESULT_CANCELED;



  // Used to receive messages from the Activity

  final Messenger inMessenger = new Messenger(new IncomingHandler());

  // Use to send message to the Activity

  private Messenger outMessenger;



  public DownloadServiceMessenger() {

    super();

    // Don't do this

    // Network Stuff will run in the main thread

    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder()

        .permitAll().build();

    StrictMode.setThreadPolicy(policy);

  }



  class IncomingHandler extends Handler {

    @Override

    public void handleMessage(Message msg) {

      Log.e("MESSAGE", "Got message");

      Bundle data = msg.getData();

      String urlPath = data.getString(DownloadServiceMessenger.URLPATH);

      String fileName = data.getString(DownloadServiceMessenger.FILENAME);

      String outputPath = download(urlPath, fileName);



      Message backMsg = Message.obtain();

      backMsg.arg1 = result;

      Bundle bundle = new Bundle();

      bundle.putString(RESULTPATH, outputPath);

      backMsg.setData(bundle);

      try {

        outMessenger.send(backMsg);

      } catch (android.os.RemoteException e1) {

        Log.w(getClass().getName(), "Exception sending message", e1);

      }

    }

  }



  private String download(String urlPath, String fileName) {

    File output = new File(Environment.getExternalStorageDirectory(),

        fileName);

    if (output.exists()) {

      output.delete();

    }



    InputStream stream = null;

    FileOutputStream fos = null;

    try {



      URL url = new URL(urlPath);

      stream = url.openConnection().getInputStream();

      InputStreamReader reader = new InputStreamReader(stream, "UTF-8");

      fos = new FileOutputStream(output.getPath());

      int next = -1;

      while ((next = reader.read()) != -1) {

        fos.write(next);

      }

      // Sucessful finished

      result = Activity.RESULT_OK;



    } catch (Exception e) {

      e.printStackTrace();

    } finally {

      if (stream != null) {

        try {

          stream.close();

        } catch (IOException e) {

          e.printStackTrace();

        }

      }

      if (fos != null) {

        try {

          fos.close();

        } catch (IOException e) {

          e.printStackTrace();

        }

      }

    }

    return output.getAbsolutePath();



  }



  @Override

  public IBinder onBind(Intent intent) {

    Bundle extras = intent.getExtras();

    // Get messager from the Activity

    if (extras != null) {

      outMessenger = (Messenger) extras.get("MESSENGER");

    }

    // Return our messenger to the Activity to get commands

    return inMessenger.getBinder();

  }

} 

Change the
main.xml
layout to the following.

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical" >



    <Button

        android:id="@+id/button1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:onClick="onClick"

        android:text="Button" />



</LinearLayout> 

Change
MainActivity
to the following.

package de.vogella.android.ownservice.messenger;



import android.app.Activity;

import android.content.ComponentName;

import android.content.Context;

import android.content.Intent;

import android.content.ServiceConnection;

import android.os.Bundle;

import android.os.Handler;

import android.os.IBinder;

import android.os.Message;

import android.os.Messenger;

import android.os.RemoteException;

import android.view.View;

import android.widget.Toast;



public class MainActivity extends Activity {

  Messenger messenger = null;



  private Handler handler = new Handler() {

    public void handleMessage(Message message) {

      Bundle data = message.getData();

      if (message.arg1 == RESULT_OK && data != null) {

        String text = data

            .getString(DownloadServiceMessenger.RESULTPATH);

        Toast.makeText(MainActivity.this, text, Toast.LENGTH_LONG)

            .show();

      }

    }

  };



  @Override

  public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.main);



  }



  private ServiceConnection conn = new ServiceConnection() {



    public void onServiceConnected(ComponentName className, IBinder binder) {

      messenger = new Messenger(binder);



    }



    public void onServiceDisconnected(ComponentName className) {

      messenger = null;

    }

  };



  protected void onResume() {

    super.onResume();

    Toast.makeText(this, "OnResume called", Toast.LENGTH_SHORT).show();

    Intent intent = null;

    intent = new Intent(this, DownloadServiceMessenger.class);

    // Create a new Messenger for the communication back

    // From the Service to the Activity

    Messenger messenger = new Messenger(handler);

    intent.putExtra("MESSENGER", messenger);



    bindService(intent, conn, Context.BIND_AUTO_CREATE);

  }



  @Override

  protected void onPause() {

    super.onPause();

    unbindService(conn);

  }



  public void onClick(View view) {

    Message msg = Message.obtain();



    try {

      Bundle bundle = new Bundle();

      bundle.putString(DownloadServiceMessenger.FILENAME, "index.html");

      bundle.putString(DownloadServiceMessenger.URLPATH,

          "http://www.vogella.com/index.html");

      msg.setData(bundle);

      messenger.send(msg);

    } catch (RemoteException e) {

      e.printStackTrace();

    }

  }

} 

Please help me to support
this article:

Before posting questions,
please see the

vogella FAQ. If you have questions or find an error in this article please
use the

www.vogella.com Google Group. I have created a short list


how to create good questions
which might also help you.