Android Interface Definition Language (AIDL)

The Android Interface Definition Language (AIDL) is similar to other IDLs: it lets you define the programming interface that both the client and service agree upon in order to communicate with each other using interprocess communication (IPC).

On Android, one process can't normally access the memory of another process. To talk, they need to decompose their objects into primitives that the operating system can understand and marshall the objects across that boundary for you. The code to do that marshalling is tedious to write, so Android handles it for you with AIDL.

Note: AIDL is necessary only if you let clients from different applications access your service for IPC and you want to handle multithreading in your service. If you don't need to perform concurrent IPC across different applications, create your interface by implementing a Binder. If you want to perform IPC but don't need to handle multithreading, implement your interface using a Messenger. Regardless, be sure that you understand bound services before implementing an AIDL.

Before you begin designing your AIDL interface, be aware that calls to an AIDL interface are direct function calls. Don't make assumptions about the thread in which the call occurs. What happens is different depending on whether the call is from a thread in the local process or a remote process:

Calls made from the local process execute in the same thread that is making the call. If this is your main UI thread, that thread continues to execute in the AIDL interface. If it is another thread, that is the one that executes your code in the service. Thus, if only local threads are accessing the service, you can completely control which threads are executing in it. But if that is the case, don't use AIDL at all; instead, create the interface by implementing a Binder.
Calls from a remote process are dispatched from a thread pool the platform maintains inside your own process. Be prepared for incoming calls from unknown threads, with multiple calls happening at the same time. In other words, an implementation of an AIDL interface must be completely thread-safe. Calls made from one thread on the same remote object arrive in order on the receiver end.
The oneway keyword modifies the behavior of remote calls. When it is used, a remote call does not block. It sends the transaction data and immediately returns. The implementation of the interface eventually receives this as a regular call from the Binder thread pool as a normal remote call. If oneway is used with a local call, there is no impact, and the call is still synchronous.

Defining an AIDL interface

Define your AIDL interface in an .aidl file using the Java programming language syntax, then save it in the source code, in the src/ directory, of both the application hosting the service and any other application that binds to the service.

When you build each application that contains the .aidl file, the Android SDK tools generate an IBinder interface based on the .aidl file and save it in the project's gen/ directory. The service must implement the IBinder interface as appropriate. The client applications can then bind to the service and call methods from the IBinder to perform IPC.

To create a bounded service using AIDL, follow these steps, which are described in the sections that follow:

Create the .aidl file
This file defines the programming interface with method signatures.
Implement the interface
The Android SDK tools generate an interface in the Java programming language based on your .aidl file. This interface has an inner abstract class named Stub that extends Binder and implements methods from your AIDL interface. You must extend the Stub class and implement the methods.
Expose the interface to clients
Implement a Service and override onBind() to return your implementation of the Stub class.

Caution: Any changes that you make to your AIDL interface after your first release must remain backward compatible to avoid breaking other applications that use your service. That is, because your .aidl file must be copied to other applications so they can access your service's interface, you must maintain support for the original interface.

Create the .aidl file

AIDL uses a simple syntax that lets you declare an interface with one or more methods that can take parameters and return values. The parameters and return values can be of any type, even other AIDL-generated interfaces.

You must construct the .aidl file using the Java programming language. Each .aidl file must define a single interface and requires only the interface declaration and method signatures.

By default, AIDL supports the following data types:

All primitive types in the Java programming language (such as int, long, char, boolean, and so on)
Arrays of any types, such as int[] or MyParcelable[]
String
CharSequence
List
All elements in the List must be one of the supported data types in this list or one of the other AIDL-generated interfaces or parcelables you declare. A List can optionally be used as a parameterized type class, such as List<String>. The actual concrete class that the other side receives is always an ArrayList, although the method is generated to use the List interface.
Map
All elements in the Map must be one of the supported data types in this list or one of the other AIDL-generated interfaces or parcelables you declare. Parameterized type maps, such as those of the form Map<String,Integer>, aren't supported. The actual concrete class that the other side receives is always a HashMap, although the method is generated to use the Map interface. Consider using a Bundle as an alternative to Map.

You must include an import statement for each additional type not listed previously, even if they are defined in the same package as your interface.

When defining your service interface, be aware that:

Methods can take zero or more parameters and can return a value or void.
All non-primitive parameters require a directional tag indicating which way the data goes: in, out, or inout (see the example below).
Primitives, String, IBinder, and AIDL-generated interfaces are in by default and can't be otherwise.

Caution: Limit the direction to what is truly needed, because marshalling parameters is expensive.
All code comments included in the .aidl file are included in the generated IBinder interface except comments before the import and package statements.
String and int constants can be defined in the AIDL interface, such as const int VERSION = 1;.
Method calls are dispatched by a transact() code, which normally is based on a method index in the interface. Because this makes versioning difficult, you can manually assign the transaction code to a method: void method() = 10;.
Nullable arguments and return types must be annotated using @nullable.

Here is an example .aidl file:

// IRemoteService.aidl
package com.example.android;

// Declare any non-default types here with import statements.

/** Example service interface */
interface IRemoteService {
    /** Request the process ID of this service. */
    int getPid();

    /** Demonstrates some basic types that you can use as parameters
     * and return values in AIDL.
     */
    void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat,
            double aDouble, String aString);
}

Save your .aidl file in your project's src/ directory. When you build your application, the SDK tools generate the IBinder interface file in your project's gen/ directory. The generated file's name matches the .aidl file's name, but with a .java extension. For example, IRemoteService.aidl results in IRemoteService.java.

If you use Android Studio, the incremental build generates the binder class almost immediately. If you do not use Android Studio, the Gradle tool generates the binder class next time you build your application. Build your project with gradle assembleDebug or gradle assembleRelease as soon as you finish writing the .aidl file, so that your code can link against the generated class.

Implement the interface

When you build your application, the Android SDK tools generate a .java interface file named after your .aidl file. The generated interface includes a subclass named Stub that is an abstract implementation of its parent interface, such as YourInterface.Stub, and declares all the methods from the .aidl file.

Note: Stub also defines a few helper methods, most notably asInterface(), which takes an IBinder, usually the one passed to a client's onServiceConnected() callback method, and returns an instance of the stub interface. For more details about how to make this cast, see the section Calling an IPC method.

To implement the interface generated from the .aidl, extend the generated Binder interface, such as YourInterface.Stub, and implement the methods inherited from the .aidl file.

Here is an example implementation of an interface called IRemoteService, defined by the preceding IRemoteService.aidl example, using an anonymous instance:

Kotlin

private val binder = object : IRemoteService.Stub() {

    override fun getPid(): Int =
            Process.myPid()

    override fun basicTypes(
            anInt: Int,
            aLong: Long,
            aBoolean: Boolean,
            aFloat: Float,
            aDouble: Double,
            aString: String
    ) {
        // Does nothing.
    }
}

Java

private final IRemoteService.Stub binder = new IRemoteService.Stub() {
    public int getPid(){
        return Process.myPid();
    }
    public void basicTypes(int anInt, long aLong, boolean aBoolean,
        float aFloat, double aDouble, String aString) {
        // Does nothing.
    }
};

Now the binder is an instance of the Stub class (a Binder), which defines the IPC interface for the service. In the next step, this instance is exposed to clients so they can interact with the service.

Be aware of a few rules when implementing your AIDL interface:

Incoming calls are not guaranteed to execute on the main thread, so you need to think about multithreading from the start and properly build your service to be thread-safe.
By default, IPC calls are synchronous. If you know that the service takes more than a few milliseconds to complete a request, don't call it from the activity's main thread. It might hang the application, resulting in Android displaying an "Application is Not Responding" dialog. Call it from a separate thread in the client.
Only the exception types listed under the reference documentation for Parcel.writeException() are sent back to the caller.

Expose the interface to clients

Once you've implemented the interface for your service, you need to expose it to clients so they can bind to it. To expose the interface for your service, extend Service and implement onBind() to return an instance of your class that implements the generated Stub, as discussed in the preceding section. Here's an example service that exposes the IRemoteService example interface to clients.

Kotlin

class RemoteService : Service() {

    override fun onCreate() {
        super.onCreate()
    }

    override fun onBind(intent: Intent): IBinder {
        // Return the interface.
        return binder
    }


    private val binder = object : IRemoteService.Stub() {
        override fun getPid(): Int {
            return Process.myPid()
        }

        override fun basicTypes(
                anInt: Int,
                aLong: Long,
                aBoolean: Boolean,
                aFloat: Float,
                aDouble: Double,
                aString: String
        ) {
            // Does nothing.
        }
    }
}

Java

public class RemoteService extends Service {
    @Override
    public void onCreate() {
        super.onCreate();
    }

    @Override
    public IBinder onBind(Intent intent) {
        // Return the interface.
        return binder;
    }

    private final IRemoteService.Stub binder = new IRemoteService.Stub() {
        public int getPid(){
            return Process.myPid();
        }
        public void basicTypes(int anInt, long aLong, boolean aBoolean,
            float aFloat, double aDouble, String aString) {
            // Does nothing.
        }
    };
}

Now, when a client, such as an activity, calls bindService() to connect to this service, the client's onServiceConnected() callback receives the binder instance returned by the service's onBind() method.

The client must also have access to the interface class. So if the client and service are in separate applications, then the client's application must have a copy of the .aidl file in its src/ directory, which generates the android.os.Binder interface, providing the client access to the AIDL methods.

When the client receives the IBinder in the onServiceConnected() callback, it must call YourServiceInterface.Stub.asInterface(service) to cast the returned parameter to YourServiceInterface type:

Kotlin

var iRemoteService: IRemoteService? = null

val mConnection = object : ServiceConnection {

    // Called when the connection with the service is established.
    override fun onServiceConnected(className: ComponentName, service: IBinder) {
        // Following the preceding example for an AIDL interface,
        // this gets an instance of the IRemoteInterface, which we can use to call on the service.
        iRemoteService = IRemoteService.Stub.asInterface(service)
    }

    // Called when the connection with the service disconnects unexpectedly.
    override fun onServiceDisconnected(className: ComponentName) {
        Log.e(TAG, "Service has unexpectedly disconnected")
        iRemoteService = null
    }
}

Java

IRemoteService iRemoteService;
private ServiceConnection mConnection = new ServiceConnection() {
    // Called when the connection with the service is established.
    public void onServiceConnected(ComponentName className, IBinder service) {
        // Following the preceding example for an AIDL interface,
        // this gets an instance of the IRemoteInterface, which we can use to call on the service.
        iRemoteService = IRemoteService.Stub.asInterface(service);
    }

    // Called when the connection with the service disconnects unexpectedly.
    public void onServiceDisconnected(ComponentName className) {
        Log.e(TAG, "Service has unexpectedly disconnected");
        iRemoteService = null;
    }
};

For more sample code, see the RemoteService.java class in ApiDemos.

Passing objects over IPC

In Android 10 (API level 29 or higher), you can define Parcelable objects directly in AIDL. Types that are supported as AIDL interface arguments and other parcelables are also supported here. This avoids the additional work to manually write marshalling code and a custom class. However, this also creates a bare struct. If custom accessors or other functionality is desired, implement Parcelable instead.

package android.graphics;

// Declare Rect so AIDL can find it and knows that it implements
// the parcelable protocol.
parcelable Rect {
    int left;
    int top;
    int right;
    int bottom;
}

The preceding code sample automatically generates a Java class with integer fields left, top, right, and bottom. All relevant marshalling code is implemented automatically, and the object can be used directly without having to add any implementation.

You can also send a custom class from one process to another through an IPC interface. However, make sure the code for your class is available to the other side of the IPC channel and your class must support the Parcelable interface. Supporting Parcelable is important because it lets the Android system decompose objects into primitives that can be marshalled across processes.

To create a custom class that supports Parcelable, do the following:

Make your class implement the Parcelable interface.
Implement writeToParcel, which takes the current state of the object and writes it to a Parcel.
Add a static field called CREATOR to your class that is an object implementing the Parcelable.Creator interface.
Finally, create an .aidl file that declares your parcelable class, as shown for the following Rect.aidl file.
If you are using a custom build process, do not add the .aidl file to your build. Similar to a header file in the C language, this .aidl file isn't compiled.

AIDL uses these methods and fields in the code it generates to marshall and unmarshall your objects.

For example, here is a Rect.aidl file to create a Rect class that's parcelable:

package android.graphics;

// Declare Rect so AIDL can find it and knows that it implements
// the parcelable protocol.
parcelable Rect;

And here is an example of how the Rect class implements the Parcelable protocol.

Kotlin

import android.os.Parcel
import android.os.Parcelable

class Rect() : Parcelable {
    var left: Int = 0
    var top: Int = 0
    var right: Int = 0
    var bottom: Int = 0

    companion object CREATOR : Parcelable.Creator<Rect> {
        override fun createFromParcel(parcel: Parcel): Rect {
            return Rect(parcel)
        }

        override fun newArray(size: Int): Array<Rect?> {
            return Array(size) { null }
        }
    }

    private constructor(inParcel: Parcel) : this() {
        readFromParcel(inParcel)
    }

    override fun writeToParcel(outParcel: Parcel, flags: Int) {
        outParcel.writeInt(left)
        outParcel.writeInt(top)
        outParcel.writeInt(right)
        outParcel.writeInt(bottom)
    }

    private fun readFromParcel(inParcel: Parcel) {
        left = inParcel.readInt()
        top = inParcel.readInt()
        right = inParcel.readInt()
        bottom = inParcel.readInt()
    }

    override fun describeContents(): Int {
        return 0
    }
}

Java

import android.os.Parcel;
import android.os.Parcelable;

public final class Rect implements Parcelable {
    public int left;
    public int top;
    public int right;
    public int bottom;

    public static final Parcelable.Creator<Rect> CREATOR = new Parcelable.Creator<Rect>() {
        public Rect createFromParcel(Parcel in) {
            return new Rect(in);
        }

        public Rect[] newArray(int size) {
            return new Rect[size];
        }
    };

    public Rect() {
    }

    private Rect(Parcel in) {
        readFromParcel(in);
    }

    public void writeToParcel(Parcel out, int flags) {
        out.writeInt(left);
        out.writeInt(top);
        out.writeInt(right);
        out.writeInt(bottom);
    }

    public void readFromParcel(Parcel in) {
        left = in.readInt();
        top = in.readInt();
        right = in.readInt();
        bottom = in.readInt();
    }

    public int describeContents() {
        return 0;
    }
}

The marshalling in the Rect class is straightforward. Take a look at the other methods on Parcel to see the other kinds of values you can write to a Parcel.

Warning: Remember the security implications of receiving data from other processes. In this case, the Rect reads four numbers from the Parcel, but it is up to you to ensure that these are within the acceptable range of values for whatever the caller is trying to do. For more information about how to keep your application secure from malware, see Security tips.

Methods with Bundle arguments containing Parcelables

If a method accepts a Bundle object that is expected to contain parcelables, make sure that you set the classloader of the Bundle by calling Bundle.setClassLoader(ClassLoader) before attempting to read from the Bundle. Otherwise, you run into ClassNotFoundException even though the parcelable is correctly defined in your application.

For example, consider the following sample .aidl file:

// IRectInsideBundle.aidl
package com.example.android;

/** Example service interface */
interface IRectInsideBundle {
    /** Rect parcelable is stored in the bundle with key "rect". */
    void saveRect(in Bundle bundle);
}

As shown in the following implementation, the ClassLoader is explicitly set in the Bundle before reading Rect:

Kotlin

private val binder = object : IRectInsideBundle.Stub() {
    override fun saveRect(bundle: Bundle) {
      bundle.classLoader = classLoader
      val rect = bundle.getParcelable<Rect>("rect")
      process(rect) // Do more with the parcelable.
    }
}

Java

private final IRectInsideBundle.Stub binder = new IRectInsideBundle.Stub() {
    public void saveRect(Bundle bundle){
        bundle.setClassLoader(getClass().getClassLoader());
        Rect rect = bundle.getParcelable("rect");
        process(rect); // Do more with the parcelable.
    }
};

Calling an IPC method

To call a remote interface defined with AIDL, take the following steps in your calling class:

Include the .aidl file in the project src/ directory.
Declare an instance of the IBinder interface, which is generated based on the AIDL.
Implement ServiceConnection.
Call Context.bindService(), passing in your ServiceConnection implementation.
In your implementation of onServiceConnected(), you receive an IBinder instance, called service. Call YourInterfaceName.Stub.asInterface((IBinder)service) to cast the returned parameter to the YourInterface type.
Call the methods that you defined on your interface. Always trap DeadObjectException exceptions, which are thrown when the connection breaks. Also, trap SecurityException exceptions, which are thrown when the two processes involved in the IPC method call have conflicting AIDL definitions.
To disconnect, call Context.unbindService() with the instance of your interface.

Bear these points in mind when calling an IPC service:

Objects are reference counted across processes.
You can send anonymous objects as method arguments.

For more information about binding to a service, read the Bound services overview.

Here is some sample code that demonstrates calling an AIDL-created service, taken from the Remote Service sample in the ApiDemos project.

Kotlin

private const val BUMP_MSG = 1

class Binding : Activity() {

    /** The primary interface you call on the service.  */
    private var mService: IRemoteService? = null

    /** Another interface you use on the service.  */
    internal var secondaryService: ISecondary? = null

    private lateinit var killButton: Button
    private lateinit var callbackText: TextView
    private lateinit var handler: InternalHandler

    private var isBound: Boolean = false

    /**
     * Class for interacting with the main interface of the service.
     */
    private val mConnection = object : ServiceConnection {

        override fun onServiceConnected(className: ComponentName, service: IBinder) {
            // This is called when the connection with the service is
            // established, giving us the service object we can use to
            // interact with the service.  We are communicating with our
            // service through an IDL interface, so get a client-side
            // representation of that from the raw service object.
            mService = IRemoteService.Stub.asInterface(service)
            killButton.isEnabled = true
            callbackText.text = "Attached."

            // We want to monitor the service for as long as we are
            // connected to it.
            try {
                mService?.registerCallback(mCallback)
            } catch (e: RemoteException) {
                // In this case, the service crashes before we can
                // do anything with it. We can count on soon being
                // disconnected (and then reconnected if it can be restarted)
                // so there is no need to do anything here.
            }

            // As part of the sample, tell the user what happened.
            Toast.makeText(
                    this@Binding,
                    R.string.remote_service_connected,
                    Toast.LENGTH_SHORT
            ).show()
        }

        override fun onServiceDisconnected(className: ComponentName) {
            // This is called when the connection with the service is
            // unexpectedly disconnected&mdash;that is, its process crashed.
            mService = null
            killButton.isEnabled = false
            callbackText.text = "Disconnected."

            // As part of the sample, tell the user what happened.
            Toast.makeText(
                    this@Binding,
                    R.string.remote_service_disconnected,
                    Toast.LENGTH_SHORT
            ).show()
        }
    }

    /**
     * Class for interacting with the secondary interface of the service.
     */
    private val secondaryConnection = object : ServiceConnection {

        override fun onServiceConnected(className: ComponentName, service: IBinder) {
            // Connecting to a secondary interface is the same as any
            // other interface.
            secondaryService = ISecondary.Stub.asInterface(service)
            killButton.isEnabled = true
        }

        override fun onServiceDisconnected(className: ComponentName) {
            secondaryService = null
            killButton.isEnabled = false
        }
    }

    private val mBindListener = View.OnClickListener {
        // Establish a couple connections with the service, binding
        // by interface names. This lets other applications be
        // installed that replace the remote service by implementing
        // the same interface.
        val intent = Intent(this@Binding, RemoteService::class.java)
        intent.action = IRemoteService::class.java.name
        bindService(intent, mConnection, Context.BIND_AUTO_CREATE)
        intent.action = ISecondary::class.java.name
        bindService(intent, secondaryConnection, Context.BIND_AUTO_CREATE)
        isBound = true
        callbackText.text = "Binding."
    }

    private val unbindListener = View.OnClickListener {
        if (isBound) {
            // If we have received the service, and hence registered with
            // it, then now is the time to unregister.
            try {
                mService?.unregisterCallback(mCallback)
            } catch (e: RemoteException) {
                // There is nothing special we need to do if the service
                // crashes.
            }

            // Detach our existing connection.
            unbindService(mConnection)
            unbindService(secondaryConnection)
            killButton.isEnabled = false
            isBound = false
            callbackText.text = "Unbinding."
        }
    }

    private val killListener = View.OnClickListener {
        // To kill the process hosting the service, we need to know its
        // PID.  Conveniently, the service has a call that returns
        // that information.
        try {
            secondaryService?.pid?.also { pid ->
                // Note that, though this API lets us request to
                // kill any process based on its PID, the kernel
                // still imposes standard restrictions on which PIDs you
                // can actually kill. Typically this means only
                // the process running your application and any additional
                // processes created by that app, as shown here. Packages
                // sharing a common UID are also able to kill each
                // other's processes.
                Process.killProcess(pid)
                callbackText.text = "Killed service process."
            }
        } catch (ex: RemoteException) {
            // Recover gracefully from the process hosting the
            // server dying.
            // For purposes of this sample, put up a notification.
            Toast.makeText(this@Binding, R.string.remote_call_failed, Toast.LENGTH_SHORT).show()
        }
    }

    // ----------------------------------------------------------------------
    // Code showing how to deal with callbacks.
    // ----------------------------------------------------------------------

    /**
     * This implementation is used to receive callbacks from the remote
     * service.
     */
    private val mCallback = object : IRemoteServiceCallback.Stub() {
        /**
         * This is called by the remote service regularly to tell us about
         * new values.  Note that IPC calls are dispatched through a thread
         * pool running in each process, so the code executing here is
         * NOT running in our main thread like most other things. So,
         * to update the UI, we need to use a Handler to hop over there.
         */
        override fun valueChanged(value: Int) {
            handler.sendMessage(handler.obtainMessage(BUMP_MSG, value, 0))
        }
    }

    /**
     * Standard initialization of this activity.  Set up the UI, then wait
     * for the user to interact with it before doing anything.
     */
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContentView(R.layout.remote_service_binding)

        // Watch for button taps.
        var button: Button = findViewById(R.id.bind)
        button.setOnClickListener(mBindListener)
        button = findViewById(R.id.unbind)
        button.setOnClickListener(unbindListener)
        killButton = findViewById(R.id.kill)
        killButton.setOnClickListener(killListener)
        killButton.isEnabled = false

        callbackText = findViewById(R.id.callback)
        callbackText.text = "Not attached."
        handler = InternalHandler(callbackText)
    }

    private class InternalHandler(
            textView: TextView,
            private val weakTextView: WeakReference<TextView> = WeakReference(textView)
    ) : Handler() {
        override fun handleMessage(msg: Message) {
            when (msg.what) {
                BUMP_MSG -> weakTextView.get()?.text = "Received from service: ${msg.arg1}"
                else -> super.handleMessage(msg)
            }
        }
    }
}

Java

public static class Binding extends Activity {
    /** The primary interface we are calling on the service. */
    IRemoteService mService = null;
    /** Another interface we use on the service. */
    ISecondary secondaryService = null;

    Button killButton;
    TextView callbackText;

    private InternalHandler handler;
    private boolean isBound;

    /**
     * Standard initialization of this activity. Set up the UI, then wait
     * for the user to interact with it before doing anything.
     */
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.remote_service_binding);

        // Watch for button taps.
        Button button = (Button)findViewById(R.id.bind);
        button.setOnClickListener(mBindListener);
        button = (Button)findViewById(R.id.unbind);
        button.setOnClickListener(unbindListener);
        killButton = (Button)findViewById(R.id.kill);
        killButton.setOnClickListener(killListener);
        killButton.setEnabled(false);

        callbackText = (TextView)findViewById(R.id.callback);
        callbackText.setText("Not attached.");
        handler = new InternalHandler(callbackText);
    }

    /**
     * Class for interacting with the main interface of the service.
     */
    private ServiceConnection mConnection = new ServiceConnection() {
        public void onServiceConnected(ComponentName className,
                IBinder service) {
            // This is called when the connection with the service is
            // established, giving us the service object we can use to
            // interact with the service.  We are communicating with our
            // service through an IDL interface, so get a client-side
            // representation of that from the raw service object.
            mService = IRemoteService.Stub.asInterface(service);
            killButton.setEnabled(true);
            callbackText.setText("Attached.");

            // We want to monitor the service for as long as we are
            // connected to it.
            try {
                mService.registerCallback(mCallback);
            } catch (RemoteException e) {
                // In this case the service crashes before we can even
                // do anything with it. We can count on soon being
                // disconnected (and then reconnected if it can be restarted)
                // so there is no need to do anything here.
            }

            // As part of the sample, tell the user what happened.
            Toast.makeText(Binding.this, R.string.remote_service_connected,
                    Toast.LENGTH_SHORT).show();
        }

        public void onServiceDisconnected(ComponentName className) {
            // This is called when the connection with the service is
            // unexpectedly disconnected&mdash;that is, its process crashed.
            mService = null;
            killButton.setEnabled(false);
            callbackText.setText("Disconnected.");

            // As part of the sample, tell the user what happened.
            Toast.makeText(Binding.this, R.string.remote_service_disconnected,
                    Toast.LENGTH_SHORT).show();
        }
    };

    /**
     * Class for interacting with the secondary interface of the service.
     */
    private ServiceConnection secondaryConnection = new ServiceConnection() {
        public void onServiceConnected(ComponentName className,
                IBinder service) {
            // Connecting to a secondary interface is the same as any
            // other interface.
            secondaryService = ISecondary.Stub.asInterface(service);
            killButton.setEnabled(true);
        }

        public void onServiceDisconnected(ComponentName className) {
            secondaryService = null;
            killButton.setEnabled(false);
        }
    };

    private OnClickListener mBindListener = new OnClickListener() {
        public void onClick(View v) {
            // Establish a couple connections with the service, binding
            // by interface names. This lets other applications be
            // installed that replace the remote service by implementing
            // the same interface.
            Intent intent = new Intent(Binding.this, RemoteService.class);
            intent.setAction(IRemoteService.class.getName());
            bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
            intent.setAction(ISecondary.class.getName());
            bindService(intent, secondaryConnection, Context.BIND_AUTO_CREATE);
            isBound = true;
            callbackText.setText("Binding.");
        }
    };

    private OnClickListener unbindListener = new OnClickListener() {
        public void onClick(View v) {
            if (isBound) {
                // If we have received the service, and hence registered with
                // it, then now is the time to unregister.
                if (mService != null) {
                    try {
                        mService.unregisterCallback(mCallback);
                    } catch (RemoteException e) {
                        // There is nothing special we need to do if the service
                        // crashes.
                    }
                }

                // Detach our existing connection.
                unbindService(mConnection);
                unbindService(secondaryConnection);
                killButton.setEnabled(false);
                isBound = false;
                callbackText.setText("Unbinding.");
            }
        }
    };

    private OnClickListener killListener = new OnClickListener() {
        public void onClick(View v) {
            // To kill the process hosting our service, we need to know its
            // PID.  Conveniently, our service has a call that returns
            // that information.
            if (secondaryService != null) {
                try {
                    int pid = secondaryService.getPid();
                    // Note that, though this API lets us request to
                    // kill any process based on its PID, the kernel
                    // still imposes standard restrictions on which PIDs you
                    // can actually kill.  Typically this means only
                    // the process running your application and any additional
                    // processes created by that app as shown here. Packages
                    // sharing a common UID are also able to kill each
                    // other's processes.
                    Process.killProcess(pid);
                    callbackText.setText("Killed service process.");
                } catch (RemoteException ex) {
                    // Recover gracefully from the process hosting the
                    // server dying.
                    // For purposes of this sample, put up a notification.
                    Toast.makeText(Binding.this,
                            R.string.remote_call_failed,
                            Toast.LENGTH_SHORT).show();
                }
            }
        }
    };

    // ----------------------------------------------------------------------
    // Code showing how to deal with callbacks.
    // ----------------------------------------------------------------------

    /**
     * This implementation is used to receive callbacks from the remote
     * service.
     */
    private IRemoteServiceCallback mCallback = new IRemoteServiceCallback.Stub() {
        /**
         * This is called by the remote service regularly to tell us about
         * new values.  Note that IPC calls are dispatched through a thread
         * pool running in each process, so the code executing here is
         * NOT running in our main thread like most other things. So,
         * to update the UI, we need to use a Handler to hop over there.
         */
        public void valueChanged(int value) {
            handler.sendMessage(handler.obtainMessage(BUMP_MSG, value, 0));
        }
    };

    private static final int BUMP_MSG = 1;

    private static class InternalHandler extends Handler {
        private final WeakReference<TextView> weakTextView;

        InternalHandler(TextView textView) {
            weakTextView = new WeakReference<>(textView);
        }

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case BUMP_MSG:
                    TextView textView = weakTextView.get();
                    if (textView != null) {
                        textView.setText("Received from service: " + msg.arg1);
                    }
                    break;
                default:
                    super.handleMessage(msg);
            }
        }
    }
}