Service 之 AIDL

Android API Guides

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1. Create .aidl文件
   定义Service接口

Caution: AIDL 做的任何改变，都必须保持后向兼容
方法支持参数和返回值，参数和返回值可以是任意类型。
1. 所有Java原型都支持（int, long, float, char ,boolean等）
2. String
3. Charsequence
4. List,元素必须是支持的数据类型，也可是其他AIDL所申明的，或者是parcelables。同时也可使用泛型申明。实际使用ArrayList来存储元素。
5. Map，也list要求相同。但不可使用泛型，实际使用HashMap来存储。

如果要使用除以上数据的类型其他类型数据，则必须使用import进行申明。

此外，在定义接口时，还需注意的有：
1. 方法可为0个或多个参数，可返回值或者void
2. 所有非原型参数，需要方向标签，in,out,inout。
3. 所有代码注释都会被生成到java接口中，除了import和package申明之前的。
4. 只支持方法，不支持静态成员变量的申明。

案例

// 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);}

1. 实现一个接口
   Android SDK tools会根据aidl文件自动生成一个java语言的编程接口，这个接口包含一个继承于Binder的抽象类和aidl中的接口方法实现。必须继承Stub然后实现方法。

保存到/src目录下，ADT tool 会在/gen目录下生成IBinder接口文件。注意包名。
生成的接口包含一个子类Stub, 是对接口的抽象实现。因此，需要继承该Stub，然后实现抽象方法。
其中Stub还有一个助手方法asInterface(),传递IBinder并返回stub接口实例。
实例代码如下：

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    }};

Caution: 注意多线程，要确保方法是线程安全的。RPC calls 通常是同步的，所以在client调用时，请使用子线程避免hand up the main thread and encounter ANR.此外，Server端不会返回Exception。

1. Expose the interface to the clients
   继承Service，重写onBind()，然后返回Stub 类的实现，即mBinder。

public class RemoteService extends Service {    @Override    public void onCreate() {        super.onCreate();    }    @Override    public IBinder onBind(Intent intent) {        // Return the interface        return mBinder;    }}

Client调用，如果与Server不再同一个Application下，那么需要将aidl文件拷贝到Client，并且保持包名的一致。

Passing Objects over IPC

支持Parcelable，将允许Android系统decompose objects into primitives that can be marshalled over processes, 意思就是允许Android系统将objects 解耦成primitives，而这些primitives可在进程间传递。
Step:
1. 让需要传递的类实现Parcelable接口，
2. 实现writeToParcel()方法，它将把对象的当前状态写到一个Parcel
3. 添加静态字段CREATOR，它时实现Parcelable.Creator接口。
4. create a aidl, 然后申明这个Parcelable 类。

aidl 申明Rect类代码如下：

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

接下来是Rect类实现Parcelable接口代码：

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 = newParcelable.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) {        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();    }}

Calling an IPC Method

调用远程服务的实例，在之前的Service节中已经出现过了。这里不妨再赘上,有效长，:）

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.            bindService(new Intent(IRemoteService.class.getName()),                    mConnection, Context.BIND_AUTO_CREATE);            bindService(new Intent(ISecondary.class.getName()),                    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);            }        }    };}