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:

Screenshot of Android service messaging example

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;
    }
}
1
578
8/24/2015 9:40:24 AM

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.

46
4/5/2013 3:01:58 PM

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