Example: Communication between Activity and Service using Messaging

Question

I couldn't find any examples of how to send messages between an activity and a service, and I have spent far too many hours figuring this out. Here is an example project for others to reference.

This example allows you to start or stop a service directly, and separately bind/unbind from the service. When the service is running, it increments a number at 10 Hz. If the activity is bound to the Service, it will display the current value. Data is transferred as an Integer and as a String so you can see how to do that two different ways. There are also buttons in the activity to send messages to the service (changes the increment-by value).

Screenshot:

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"       package="com.exampleservice"       android:versionCode="1"       android:versionName="1.0">     <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=".MyService"></service>     </application>     <uses-sdk android:minSdkVersion="8" /> </manifest> 

res\values\strings.xml:

<?xml version="1.0" encoding="utf-8"?> <resources>     <string name="app_name">ExampleService</string>     <string name="service_started">Example Service started</string>     <string name="service_label">Example Service Label</string> </resources> 

res\layout\main.xml:

<RelativeLayout     android:id="@+id/RelativeLayout01"     android:layout_width="fill_parent"     android:layout_height="wrap_content" >      <Button         android:id="@+id/btnStart"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="Start Service" >     </Button>      <Button         android:id="@+id/btnStop"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_alignParentRight="true"         android:text="Stop Service" >     </Button> </RelativeLayout>  <RelativeLayout     android:id="@+id/RelativeLayout02"     android:layout_width="fill_parent"     android:layout_height="wrap_content" >      <Button         android:id="@+id/btnBind"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="Bind to Service" >     </Button>      <Button         android:id="@+id/btnUnbind"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_alignParentRight="true"         android:text="Unbind from Service" >     </Button> </RelativeLayout>  <TextView     android:id="@+id/textStatus"     android:layout_width="fill_parent"     android:layout_height="wrap_content"     android:text="Status Goes Here"     android:textSize="24sp" />  <TextView     android:id="@+id/textIntValue"     android:layout_width="fill_parent"     android:layout_height="wrap_content"     android:text="Integer Value Goes Here"     android:textSize="24sp" />  <TextView     android:id="@+id/textStrValue"     android:layout_width="fill_parent"     android:layout_height="wrap_content"     android:text="String Value Goes Here"     android:textSize="24sp" />  <RelativeLayout     android:id="@+id/RelativeLayout03"     android:layout_width="fill_parent"     android:layout_height="wrap_content" >      <Button         android:id="@+id/btnUpby1"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="Increment by 1" >     </Button>      <Button         android:id="@+id/btnUpby10"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_alignParentRight="true"         android:text="Increment by 10" >     </Button> </RelativeLayout> 

src\com.exampleservice\MainActivity.java:

package com.exampleservice;  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.util.Log; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.TextView;  public class MainActivity extends Activity {     Button btnStart, btnStop, btnBind, btnUnbind, btnUpby1, btnUpby10;     TextView textStatus, textIntValue, textStrValue;     Messenger mService = null;     boolean mIsBound;     final Messenger mMessenger = new Messenger(new IncomingHandler());      class IncomingHandler extends Handler {         @Override         public void handleMessage(Message msg) {             switch (msg.what) {             case MyService.MSG_SET_INT_VALUE:                 textIntValue.setText("Int Message: " + msg.arg1);                 break;             case MyService.MSG_SET_STRING_VALUE:                 String str1 = msg.getData().getString("str1");                 textStrValue.setText("Str Message: " + str1);                 break;             default:                 super.handleMessage(msg);             }         }     }     private ServiceConnection mConnection = new ServiceConnection() {         public void onServiceConnected(ComponentName className, IBinder service) {             mService = new Messenger(service);             textStatus.setText("Attached.");             try {                 Message msg = Message.obtain(null, MyService.MSG_REGISTER_CLIENT);                 msg.replyTo = mMessenger;                 mService.send(msg);             }             catch (RemoteException e) {                 // In this case the service has crashed before we could even do anything with it             }         }          public void onServiceDisconnected(ComponentName className) {             // This is called when the connection with the service has been unexpectedly disconnected - process crashed.             mService = null;             textStatus.setText("Disconnected.");         }     };      @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.main);         btnStart = (Button)findViewById(R.id.btnStart);         btnStop = (Button)findViewById(R.id.btnStop);         btnBind = (Button)findViewById(R.id.btnBind);         btnUnbind = (Button)findViewById(R.id.btnUnbind);         textStatus = (TextView)findViewById(R.id.textStatus);         textIntValue = (TextView)findViewById(R.id.textIntValue);         textStrValue = (TextView)findViewById(R.id.textStrValue);         btnUpby1 = (Button)findViewById(R.id.btnUpby1);         btnUpby10 = (Button)findViewById(R.id.btnUpby10);          btnStart.setOnClickListener(btnStartListener);         btnStop.setOnClickListener(btnStopListener);         btnBind.setOnClickListener(btnBindListener);         btnUnbind.setOnClickListener(btnUnbindListener);         btnUpby1.setOnClickListener(btnUpby1Listener);         btnUpby10.setOnClickListener(btnUpby10Listener);          restoreMe(savedInstanceState);          CheckIfServiceIsRunning();     }      @Override     protected void onSaveInstanceState(Bundle outState) {         super.onSaveInstanceState(outState);         outState.putString("textStatus", textStatus.getText().toString());         outState.putString("textIntValue", textIntValue.getText().toString());         outState.putString("textStrValue", textStrValue.getText().toString());     }     private void restoreMe(Bundle state) {         if (state!=null) {             textStatus.setText(state.getString("textStatus"));             textIntValue.setText(state.getString("textIntValue"));             textStrValue.setText(state.getString("textStrValue"));         }     }     private void CheckIfServiceIsRunning() {         //If the service is running when the activity starts, we want to automatically bind to it.         if (MyService.isRunning()) {             doBindService();         }     }      private OnClickListener btnStartListener = new OnClickListener() {         public void onClick(View v){             startService(new Intent(MainActivity.this, MyService.class));         }     };     private OnClickListener btnStopListener = new OnClickListener() {         public void onClick(View v){             doUnbindService();             stopService(new Intent(MainActivity.this, MyService.class));         }     };     private OnClickListener btnBindListener = new OnClickListener() {         public void onClick(View v){             doBindService();         }     };     private OnClickListener btnUnbindListener = new OnClickListener() {         public void onClick(View v){             doUnbindService();         }     };     private OnClickListener btnUpby1Listener = new OnClickListener() {         public void onClick(View v){             sendMessageToService(1);         }     };     private OnClickListener btnUpby10Listener = new OnClickListener() {         public void onClick(View v){             sendMessageToService(10);         }     };     private void sendMessageToService(int intvaluetosend) {         if (mIsBound) {             if (mService != null) {                 try {                     Message msg = Message.obtain(null, MyService.MSG_SET_INT_VALUE, intvaluetosend, 0);                     msg.replyTo = mMessenger;                     mService.send(msg);                 }                 catch (RemoteException e) {                 }             }         }     }       void doBindService() {         bindService(new Intent(this, MyService.class), mConnection, Context.BIND_AUTO_CREATE);         mIsBound = true;         textStatus.setText("Binding.");     }     void doUnbindService() {         if (mIsBound) {             // If we have received the service, and hence registered with it, then now is the time to unregister.             if (mService != null) {                 try {                     Message msg = Message.obtain(null, MyService.MSG_UNREGISTER_CLIENT);                     msg.replyTo = mMessenger;                     mService.send(msg);                 }                 catch (RemoteException e) {                     // There is nothing special we need to do if the service has crashed.                 }             }             // Detach our existing connection.             unbindService(mConnection);             mIsBound = false;             textStatus.setText("Unbinding.");         }     }      @Override     protected void onDestroy() {         super.onDestroy();         try {             doUnbindService();         }         catch (Throwable t) {             Log.e("MainActivity", "Failed to unbind from the service", t);         }     } } 

src\com.exampleservice\MyService.java:

package com.exampleservice;  import java.util.ArrayList; import java.util.Timer; import java.util.TimerTask;  import android.app.Notification; import android.app.NotificationManager; import android.app.PendingIntent; import android.app.Service; import android.content.Intent; 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.util.Log;  public class MyService extends Service {     private NotificationManager nm;     private Timer timer = new Timer();     private int counter = 0, incrementby = 1;     private static boolean isRunning = false;      ArrayList<Messenger> mClients = new ArrayList<Messenger>(); // Keeps track of all current registered clients.     int mValue = 0; // Holds last value set by a client.     static final int MSG_REGISTER_CLIENT = 1;     static final int MSG_UNREGISTER_CLIENT = 2;     static final int MSG_SET_INT_VALUE = 3;     static final int MSG_SET_STRING_VALUE = 4;     final Messenger mMessenger = new Messenger(new IncomingHandler()); // Target we publish for clients to send messages to IncomingHandler.       @Override     public IBinder onBind(Intent intent) {         return mMessenger.getBinder();     }     class IncomingHandler extends Handler { // Handler of incoming messages from clients.         @Override         public void handleMessage(Message msg) {             switch (msg.what) {             case MSG_REGISTER_CLIENT:                 mClients.add(msg.replyTo);                 break;             case MSG_UNREGISTER_CLIENT:                 mClients.remove(msg.replyTo);                 break;             case MSG_SET_INT_VALUE:                 incrementby = msg.arg1;                 break;             default:                 super.handleMessage(msg);             }         }     }     private void sendMessageToUI(int intvaluetosend) {         for (int i=mClients.size()-1; i>=0; i--) {             try {                 // Send data as an Integer                 mClients.get(i).send(Message.obtain(null, MSG_SET_INT_VALUE, intvaluetosend, 0));                  //Send data as a String                 Bundle b = new Bundle();                 b.putString("str1", "ab" + intvaluetosend + "cd");                 Message msg = Message.obtain(null, MSG_SET_STRING_VALUE);                 msg.setData(b);                 mClients.get(i).send(msg);              }             catch (RemoteException e) {                 // The client is dead. Remove it from the list; we are going through the list from back to front so this is safe to do inside the loop.                 mClients.remove(i);             }         }     }      @Override     public void onCreate() {         super.onCreate();         Log.i("MyService", "Service Started.");         showNotification();         timer.scheduleAtFixedRate(new TimerTask(){ public void run() {onTimerTick();}}, 0, 100L);         isRunning = true;     }     private void showNotification() {         nm = (NotificationManager)getSystemService(NOTIFICATION_SERVICE);         // In this sample, we'll use the same text for the ticker and the expanded notification         CharSequence text = getText(R.string.service_started);         // Set the icon, scrolling text and timestamp         Notification notification = new Notification(R.drawable.icon, text, System.currentTimeMillis());         // The PendingIntent to launch our activity if the user selects this notification         PendingIntent contentIntent = PendingIntent.getActivity(this, 0, new Intent(this, MainActivity.class), 0);         // Set the info for the views that show in the notification panel.         notification.setLatestEventInfo(this, getText(R.string.service_label), text, contentIntent);         // Send the notification.         // We use a layout id because it is a unique number.  We use it later to cancel.         nm.notify(R.string.service_started, notification);     }     @Override     public int onStartCommand(Intent intent, int flags, int startId) {         Log.i("MyService", "Received start id " + startId + ": " + intent);         return START_STICKY; // run until explicitly stopped.     }      public static boolean isRunning()     {         return isRunning;     }       private void onTimerTick() {         Log.i("TimerTick", "Timer doing work." + counter);         try {             counter += incrementby;             sendMessageToUI(counter);          }         catch (Throwable t) { //you should always ultimately catch all exceptions in timer tasks.             Log.e("TimerTick", "Timer Tick Failed.", t);         }     }      @Override     public void onDestroy() {         super.onDestroy();         if (timer != null) {timer.cancel();}         counter=0;         nm.cancel(R.string.service_started); // Cancel the persistent notification.         Log.i("MyService", "Service Stopped.");         isRunning = false;     } } 

Answer 1

Look at the LocalService example.

Your Service returns an instance of itself to consumers who call onBind. Then you can directly interact with the service, e.g. registering your own listener interface with the service, so that you can get callbacks.

Answer 2

For sending data to a service you can use:

Intent intent = new Intent(getApplicationContext(), YourService.class); intent.putExtra("SomeData","ItValue"); startService(intent); 

And after in service in onStartCommand() get data from intent.

For sending data or event from a service to an application (for one or more activities):

private void sendBroadcastMessage(String intentFilterName, int arg1, String extraKey) {     Intent intent = new Intent(intentFilterName);     if (arg1 != -1 && extraKey != null) {         intent.putExtra(extraKey, arg1);     }     sendBroadcast(intent); } 

This method is calling from your service. You can simply send data for your Activity.

private void someTaskInYourService(){      //For example you downloading from server 1000 files     for(int i = 0; i < 1000; i++) {         Thread.sleep(5000) // 5 seconds. Catch in try-catch block         sendBroadCastMessage(Events.UPDATE_DOWNLOADING_PROGRESSBAR, i,0,"up_download_progress");     } 

For receiving an event with data, create and register method registerBroadcastReceivers() in your activity:

private void registerBroadcastReceivers(){     broadcastReceiver = new BroadcastReceiver() {         @Override         public void onReceive(Context context, Intent intent) {             int arg1 = intent.getIntExtra("up_download_progress",0);             progressBar.setProgress(arg1);         }     };     IntentFilter progressfilter = new IntentFilter(Events.UPDATE_DOWNLOADING_PROGRESS);     registerReceiver(broadcastReceiver,progressfilter); 

For sending more data, you can modify method sendBroadcastMessage();. Remember: you must register broadcasts in onResume() & unregister in onStop() methods!

UPDATE

Please don't use my type of communication between Activity & Service. This is the wrong way. For a better experience please use special libs, such us:

1) EventBus from greenrobot

2) Otto from Square Inc

P.S. I'm only using EventBus from greenrobot in my projects,