Explanation of AIDL in Android

Explanation of AIDL in Android
Introduction

Android Interface Definition Language (AIDL) and Android Interface Definition Language. The memory cannot be shared among processes in the system. Therefore, you need to provide some mechanisms for Interprocess communication (IPC) between different processes ). AIDL solves this problem.
Read this article to learn about the Service

Create a. aidl File

Aidl is written in Java syntax and is suffixed with. aidl.

Each aidl file must define an interface. The declared method in this interface cannot have the static attribute (field) in aidl. aidl supports basic data types, when you need to use additional data types, you need to import them, even if they are in the same package as this file. Example

// IRemoteService.aidlpackage com.example.android;// Declare any non-default types here with import statements/** Example service interface */interface IRemoteService {    /** Request the process ID of this service, to do evil things with it. */    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);}

Store the aidl file in the src/directory. When you build the project, the SDK tool will generate a. java file with the same name as the. aidl file under the gen/directory.

Implementation Interface

The generated IRemoteService. java is as follows:

public interface IRemoteService extends android.os.IInterface{/** Local-side IPC implementation stub class. */public static abstract class Stub extends android.os.Binder implements com.spark.meizi.IRemoteService{private static final java.lang.String DESCRIPTOR = "com.spark.meizi.IRemoteService";/** Construct the stub at attach it to the interface. */public Stub(){this.attachInterface(this, DESCRIPTOR);}/** * Cast an IBinder object into an com.spark.meizi.IRemoteService interface, * generating a proxy if needed. */public static com.spark.meizi.IRemoteService asInterface(android.os.IBinder obj){if ((obj==null)) {return null;}android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);if (((iin!=null)&&(iin instanceof com.spark.meizi.IRemoteService))) {return ((com.spark.meizi.IRemoteService)iin);}return new com.spark.meizi.IRemoteService.Stub.Proxy(obj);}@Override public android.os.IBinder asBinder(){return this;}@Override public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException{switch (code){case INTERFACE_TRANSACTION:{reply.writeString(DESCRIPTOR);return true;}case TRANSACTION_basicTypes:{data.enforceInterface(DESCRIPTOR);int _arg0;_arg0 = data.readInt();long _arg1;_arg1 = data.readLong();boolean _arg2;_arg2 = (0!=data.readInt());float _arg3;_arg3 = data.readFloat();double _arg4;_arg4 = data.readDouble();java.lang.String _arg5;_arg5 = data.readString();this.basicTypes(_arg0, _arg1, _arg2, _arg3, _arg4, _arg5);reply.writeNoException();return true;}}return super.onTransact(code, data, reply, flags);}private static class Proxy implements com.spark.meizi.IRemoteService{private android.os.IBinder mRemote;Proxy(android.os.IBinder remote){mRemote = remote;}@Override public android.os.IBinder asBinder(){return mRemote;}public java.lang.String getInterfaceDescriptor(){return DESCRIPTOR;}/**     * Demonstrates some basic types that you can use as parameters     * and return values in AIDL.     */@Override public void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, java.lang.String aString) throws android.os.RemoteException{android.os.Parcel _data = android.os.Parcel.obtain();android.os.Parcel _reply = android.os.Parcel.obtain();try {_data.writeInterfaceToken(DESCRIPTOR);_data.writeInt(anInt);_data.writeLong(aLong);_data.writeInt(((aBoolean)?(1):(0)));_data.writeFloat(aFloat);_data.writeDouble(aDouble);_data.writeString(aString);mRemote.transact(Stub.TRANSACTION_basicTypes, _data, _reply, 0);_reply.readException();}finally {_reply.recycle();_data.recycle();}}}static final int TRANSACTION_basicTypes = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);}/**     * Demonstrates some basic types that you can use as parameters     * and return values in AIDL.     */public void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, java.lang.String aString) throws android.os.RemoteException;}

There isInternal class StubThis is an abstract Implementation of the parent interface and declares all methods in aidl. To implement the interfaces generated by aidl, We need to inherit Stub and implement the methods inherited from aidl. The following is an example of using anonymous classes.

private final IRemoteService.Stub mBinder = 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    }};

In this way, mBinder is a Stub instance. The next step is how to use it on the client and interact with the service.
Note:

Requests are not guaranteed to be executed in the main thread. Therefore, from construction to use, the security of the Service thread should be considered. By default, requests are synchronized, therefore, do not send requests in the main thread. All exceptions will not be returned to the requester (Caller) using interfaces in the Client.

After you have implemented your Service, you need to expose it to the Client so that the Client can bind it. Inherit the Service and implement the onBind () method to return an instance that implements Stub. The following is an example of exposing IRemoteService to the Client:

public class RemoteService extends Service {    @Override    public void onCreate() {        super.onCreate();    }    @Override    public IBinder onBind(Intent intent) {        // Return the interface        return mBinder;    }    private final IRemoteService.Stub mBinder = 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 client (for example, an Activity) can call bindService () to connect to this Service, use onServiceConnected () to receive the mBinder returned by onBind () in the Service, and use YourServiceInterface. stub. asInterface (service) to convert the returned mBinder to YourServiceInterface type. Example:

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

Note:
If the Service and Client are in two different applications, the src/directory of the Client Application must also have the corresponding. aidl file.

Example of a Client

public static class Binding extends Activity {    /** The primary interface we will be calling on the service. */    IRemoteService mService = null;    /** Another interface we use on the service. */    ISecondary mSecondaryService = null;    Button mKillButton;    TextView mCallbackText;    private boolean mIsBound;    /**     * Standard initialization of this activity.  Set up the UI, then wait     * for the user to poke it before doing anything.     */    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.remote_service_binding);        // Watch for button clicks.        Button button = (Button)findViewById(R.id.bind);        button.setOnClickListener(mBindListener);        button = (Button)findViewById(R.id.unbind);        button.setOnClickListener(mUnbindListener);        mKillButton = (Button)findViewById(R.id.kill);        mKillButton.setOnClickListener(mKillListener);        mKillButton.setEnabled(false);        mCallbackText = (TextView)findViewById(R.id.callback);        mCallbackText.setText("Not attached.");    }    /**     * 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 has been            // 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);            mKillButton.setEnabled(true);            mCallbackText.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 has crashed before we could 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 has been            // unexpectedly disconnected -- that is, its process crashed.            mService = null;            mKillButton.setEnabled(false);            mCallbackText.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 mSecondaryConnection = new ServiceConnection() {        public void onServiceConnected(ComponentName className,                IBinder service) {            // Connecting to a secondary interface is the same as any            // other interface.            mSecondaryService = ISecondary.Stub.asInterface(service);            mKillButton.setEnabled(true);        }        public void onServiceDisconnected(ComponentName className) {            mSecondaryService = null;            mKillButton.setEnabled(false);        }    };    private OnClickListener mBindListener = new OnClickListener() {        public void onClick(View v) {            // Establish a couple connections with the service, binding            // by interface names.  This allows other applications to 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, mSecondaryConnection, Context.BIND_AUTO_CREATE);            mIsBound = true;            mCallbackText.setText("Binding.");        }    };    private OnClickListener mUnbindListener = new OnClickListener() {        public void onClick(View v) {            if (mIsBound) {                // 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                        // has crashed.                    }                }                // Detach our existing connection.                unbindService(mConnection);                unbindService(mSecondaryConnection);                mKillButton.setEnabled(false);                mIsBound = false;                mCallbackText.setText("Unbinding.");            }        }    };    private OnClickListener mKillListener = 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 will return            // to us that information.            if (mSecondaryService != null) {                try {                    int pid = mSecondaryService.getPid();                    // Note that, though this API allows us to request to                    // kill any process based on its PID, the kernel will                    // still impose standard restrictions on which PIDs you                    // are actually able to 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 will also be able to kill each                    // other's processes.                    Process.killProcess(pid);                    mCallbackText.setText("Killed service process.");                } catch (RemoteException ex) {                    // Recover gracefully from the process hosting the                    // server dying.                    // Just for purposes of the 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 will         * NOT be 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) {            mHandler.sendMessage(mHandler.obtainMessage(BUMP_MSG, value, 0));        }    };    private static final int BUMP_MSG = 1;    private Handler mHandler = new Handler() {        @Override public void handleMessage(Message msg) {            switch (msg.what) {                case BUMP_MSG:                    mCallbackText.setText("Received from service: " + msg.arg1);                    break;                default:                    super.handleMessage(msg);            }        }    };}