在Android中，如果我們需要在不同進程間實現通信，有很多種方式，其中最普通的方式就是AIDL。

AIDL（Android Interface Definition Language）是一種接口定義語言，編譯器通過*.aidl文件的描述信息生成符合通信協議的Java代碼，我們無需自己去寫這段繁雜的代碼，只需要在需要的時候調用即可，通過這種方式我們就可以完成進程間的通信工作。本文Demo爲Android開發藝術探索的例子，姑且當做學習筆記記錄下AIDL的基本用法。廢話不說，先上乾貨。

1.準備好AIDL文件

IBookManager.aidl

package com.ryg.chapter_2.aidl;

import com.ryg.chapter_2.aidl.Book;
import com.ryg.chapter_2.aidl.IOnNewBookArrivedListener;

interface IBookManager {
     List<Book> getBookList();
     void addBook(in Book book);
     void registerListener(IOnNewBookArrivedListener listener);
     void unregisterListener(IOnNewBookArrivedListener listener);
}

由於AIDL文件包含自定義類Book，所以要添加一個Book類的聲明文件，很簡單一行代碼搞定

Book.aidl

package com.ryg.chapter_2.aidl;

parcelable Book;

如果你打開了Eclipse的自動編譯功能就可以看到gen目錄下面自動生成了對應的java文件

2.自定義服務類

BookManagerService.java

package com.ryg.chapter_2.aidl;

import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.atomic.AtomicBoolean;

import android.app.Service;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.os.Binder;
import android.os.IBinder;
import android.os.Parcel;
import android.os.RemoteCallbackList;
import android.os.RemoteException;
import android.os.SystemClock;
import android.util.Log;

public class BookManagerService extends Service {

    private static final String TAG = "BMS";

    private AtomicBoolean mIsServiceDestoryed = new AtomicBoolean(false);

    private CopyOnWriteArrayList<Book> mBookList = new CopyOnWriteArrayList<Book>();
    // private CopyOnWriteArrayList<IOnNewBookArrivedListener> mListenerList =
    // new CopyOnWriteArrayList<IOnNewBookArrivedListener>();

    private RemoteCallbackList<IOnNewBookArrivedListener> mListenerList = new RemoteCallbackList<IOnNewBookArrivedListener>();

    private Binder mBinder = new IBookManager.Stub() {

        @Override
        public List<Book> getBookList() throws RemoteException {
            SystemClock.sleep(5000);
            return mBookList;
        }

        @Override
        public void addBook(Book book) throws RemoteException {
            mBookList.add(book);
        }

        public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
                throws RemoteException {
            int check = checkCallingOrSelfPermission("com.ryg.chapter_2.permission.ACCESS_BOOK_SERVICE");
            Log.d(TAG, "check=" + check);
            if (check == PackageManager.PERMISSION_DENIED) {
                return false;
            }

            String packageName = null;
            String[] packages = getPackageManager().getPackagesForUid(
                    getCallingUid());
            if (packages != null && packages.length > 0) {
                packageName = packages[0];
            }
            Log.d(TAG, "onTransact: " + packageName);
            if (!packageName.startsWith("com.ryg")) {
                return false;
            }

            return super.onTransact(code, data, reply, flags);
        }

        @Override
        public void registerListener(IOnNewBookArrivedListener listener)
                throws RemoteException {
            mListenerList.register(listener);

            final int N = mListenerList.beginBroadcast();
            mListenerList.finishBroadcast();
            Log.d(TAG, "registerListener, current size:" + N);
        }

        @Override
        public void unregisterListener(IOnNewBookArrivedListener listener)
                throws RemoteException {
            boolean success = mListenerList.unregister(listener);

            if (success) {
                Log.d(TAG, "unregister success.");
            } else {
                Log.d(TAG, "not found, can not unregister.");
            }
            final int N = mListenerList.beginBroadcast();
            mListenerList.finishBroadcast();
            Log.d(TAG, "unregisterListener, current size:" + N);
        };

    };

    @Override
    public void onCreate() {
        super.onCreate();
        mBookList.add(new Book(1, "Android"));
        mBookList.add(new Book(2, "Ios"));
        new Thread(new ServiceWorker()).start();
    }

    @Override
    public IBinder onBind(Intent intent) {
        int check = checkCallingOrSelfPermission("com.ryg.chapter_2.permission.ACCESS_BOOK_SERVICE");
        Log.d(TAG, "onbind check=" + check);
        if (check == PackageManager.PERMISSION_DENIED) {
            return null;
        }
        return mBinder;
    }

    @Override
    public void onDestroy() {
        mIsServiceDestoryed.set(true);
        super.onDestroy();
    }

    private void onNewBookArrived(Book book) throws RemoteException {
        mBookList.add(book);
        final int N = mListenerList.beginBroadcast();
        for (int i = 0; i < N; i++) {
            IOnNewBookArrivedListener l = mListenerList.getBroadcastItem(i);
            if (l != null) {
                try {
                    l.onNewBookArrived(book);
                } catch (RemoteException e) {
                    e.printStackTrace();
                }
            }
        }
        mListenerList.finishBroadcast();
    }

    private class ServiceWorker implements Runnable {
        @Override
        public void run() {
            // do background processing here.....
            while (!mIsServiceDestoryed.get()) {
                try {
                    Thread.sleep(5000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                int bookId = mBookList.size() + 1;
                Book newBook = new Book(bookId, "new book#" + bookId);
                try {
                    onNewBookArrived(newBook);
                } catch (RemoteException e) {
                    e.printStackTrace();
                }
            }
        }
    }

}

這個類有點長，其實不太適合作爲介紹AIDL的入門用法，我們只看其中的關鍵方法，用僞代碼表示爲

    @Override
    public IBinder onBind(Intent intent) {
       
        return new IBookManager.Stub() {

        @Override
        public List<Book> getBookList() throws RemoteException {
           // Todo
            return null;
        }

        @Override
        public void addBook(Book book) throws RemoteException {
            //Todo
        };
    }

本質就是重寫父類service的onBind方法，返回AIDL文件生成的interface對應的Stub()方法。服務器端的Service就是這麼簡單。

3.客戶端調用

BookManagerActivity.java

package com.ryg.chapter_2.aidl;

import java.util.List;
import com.ryg.chapter_2.R;
import com.ryg.chapter_2.aidl.IBookManager;
import com.ryg.chapter_2.utils.MyConstants;
import android.annotation.SuppressLint;
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.RemoteException;
import android.util.Log;
import android.view.View;
import android.widget.Toast;

public class BookManagerActivity extends Activity {

    private static final String TAG = "BookManagerActivity";
    private static final int MESSAGE_NEW_BOOK_ARRIVED = 1;

    private IBookManager mRemoteBookManager;

    @SuppressLint("HandlerLeak")
    private Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
            case MESSAGE_NEW_BOOK_ARRIVED:
                Log.d(TAG, "receive new book :" + msg.obj);
                break;
            default:
                super.handleMessage(msg);
            }
        }
    };

    private IBinder.DeathRecipient mDeathRecipient = new IBinder.DeathRecipient() {
        @Override
        public void binderDied() {
            Log.d(TAG, "binder died. tname:" + Thread.currentThread().getName());
            if (mRemoteBookManager == null)
                return;
            mRemoteBookManager.asBinder().unlinkToDeath(mDeathRecipient, 0);
            mRemoteBookManager = null;
            // TODO:這裏重新綁定遠程Service
        }
    };

    private ServiceConnection mConnection = new ServiceConnection() {
        public void onServiceConnected(ComponentName className, IBinder service) {
            IBookManager bookManager = IBookManager.Stub.asInterface(service);
            mRemoteBookManager = bookManager;
            try {
                mRemoteBookManager.asBinder().linkToDeath(mDeathRecipient, 0);
                List<Book> list = bookManager.getBookList();
                Log.i(TAG, "query book list, list type:"
                        + list.getClass().getCanonicalName());
                Log.i(TAG, "query book list:" + list.toString());
                Book newBook = new Book(3, "Android進階");
                bookManager.addBook(newBook);
                Log.i(TAG, "add book:" + newBook);
                List<Book> newList = bookManager.getBookList();
                Log.i(TAG, "query book list:" + newList.toString());
                bookManager.registerListener(mOnNewBookArrivedListener);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }

        public void onServiceDisconnected(ComponentName className) {
            mRemoteBookManager = null;
            Log.d(TAG, "onServiceDisconnected. tname:" + Thread.currentThread().getName());
        }
    };

    private IOnNewBookArrivedListener mOnNewBookArrivedListener = new IOnNewBookArrivedListener.Stub() {

        @Override
        public void onNewBookArrived(Book newBook) throws RemoteException {
            mHandler.obtainMessage(MESSAGE_NEW_BOOK_ARRIVED, newBook)
                    .sendToTarget();
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_book_manager);
        Intent intent = new Intent(this, BookManagerService.class);
        bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
    }

    public void onButton1Click(View view) {
        Toast.makeText(this, "click button1", Toast.LENGTH_SHORT).show();
        new Thread(new Runnable() {

            @Override
            public void run() {
                if (mRemoteBookManager != null) {
                    try {
                        List<Book> newList = mRemoteBookManager.getBookList();
                    } catch (RemoteException e) {
                        e.printStackTrace();
                    }
                }
            }
        }).start();
    }

    @Override
    protected void onDestroy() {
        if (mRemoteBookManager != null
                && mRemoteBookManager.asBinder().isBinderAlive()) {
            try {
                Log.i(TAG, "unregister listener:" + mOnNewBookArrivedListener);
                mRemoteBookManager
                        .unregisterListener(mOnNewBookArrivedListener);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }
        unbindService(mConnection);
        super.onDestroy();
    }

}

跟服務器端一樣，我們主要看核心部分

 private ServiceConnection mConnection = new ServiceConnection() {
        public void onServiceConnected(ComponentName className, IBinder service) {
            IBookManager bookManager = IBookManager.Stub.asInterface(service);
            //bookManager.addBook(book)
            //bookManager.getBookList()
        }

        public void onServiceDisconnected(ComponentName className) {
            mRemoteBookManager = null;
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_book_manager);
        Intent intent = new Intent(this, BookManagerService.class);
        bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
    }

 protected void onDestroy() {
            ...
        unbindService(mConnection);
        super.onDestroy();
    }

在客戶端Activity中OnCreate方法中bindService,onDestory中unbindService

請注意該interface 中的onServiceConnected()方法的第二個變量Service。當客戶端請求AmS 啓動某個Service 後，該Service 如果正常啓動，那麼AmS 就會遠程調用ActivityThread 類中的ApplicationThread對象，調用的參數中會包含Service 的Binder 引用，然後在ApplicationThread 中會回調bindService 中的conn 接口。因此，在客戶端中，可以在onServiceConnected()方法中將其參數Service 保存爲一個全局變量，從而在客戶端的任何地方都可以隨時調用該遠程服務。

有幾點需要注意的

1.本Demo服務器端客戶端在同一個應用中，所以可以直接用顯式Intent作爲bindService的第一個參數，如果客服端服務器端在不同的應用，客戶端AIDL文件要跟客戶端保持一致，可以用隱式Intent作爲bindService的第一個參數。

2.本應用雖然在一個應用中，通過process：remote配置Service在另外的進程中，所以跟兩個應用跨進程IPC調用是一樣的效果。

3.如果服務器端和客戶端在同一個進程，則不會調用AIDL文件對應Interface中實現的onTransact方法，直接調用對應實現方法。否則跨進程會通過onTransact調用對應的實現方法。這個邏輯是由Stub類的內部代理Proxy來完成的。

4.本Demo中 mDeathRecipient = new IBinder.DeathRecipient(){ public void binderDied() {...}}；

 mRemoteBookManager.asBinder().linkToDeath(mDeathRecipient, 0);

當遠程服務異常掛掉的情況下，會調用binderDied的方法，在其中可以解除關聯

 mRemoteBookManager.asBinder().unlinkToDeath(mDeathRecipient, 0);

4.使用總結

1.AIDL文件ready,IServiceManager.aidl
2.服務器：MyService extends Service 重寫onBind方法返回Stub()實例
3.客戶端：ServiceConnection實例serviceConnection onServiceConnected方法得到IBinder（android.os.BinderProxy）參數獲取IServiceManager實例(IServiceManager$Stub$Proxy)，接下來調用方法。
4.若客戶端服務器端在一個進程，3中onServiceConnected方法得到IBinder和IServiceManager爲同一個MyService對象，且不會調用transact方法。

最後附上源碼：http://download.csdn.net/detail/tianmi1988/9320963，對總結中的3、4點讀者可以添加打印自行驗證。

Android IPC之AIDL

1.準備好AIDL文件

2.自定義服務類

3.客戶端調用

4.使用總結

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