Android接口描述语言（AIDL）
AIDL定义客户端和服务器端都遵守的接口，进行进程间通信。
Note:AIDL使用场景：来自多个应用的客户端通过IPC访问服务，并且服务需要处理多线程的场景；
如果你没有来自不同客户端的并发场景，建议使用Binder接口；如果你需要处理IPC，但是没有多线程的场景，建议使用Messenger。（这两种用法在http://www.cnblogs.com/konger/p/3923518.html有介绍）
AIDL接口调用是直接的函数调用方式，同进程和其他进程调用之间有所区别：
- 同进程调用AIDL接口，AIDL接口代码在调用该接口的线程中完成。（如果仅仅是同进程调用AIDL，就建议用Binder接口）
- 其他进程调用AIDL，那们会在AIDL所属进程的线程池中分派一个线程来执行AIDL代码，所以AIDL可能被多线程同时访问，需要保证线程安全。
- 可以通过oneway关键字来修改远程调用的行为属性，如果使用这个关键字，那么远程调用会直接返回而不等结果，不会阻塞调用者线程的运行。关键字oneway对于本地调用没有任何影响。（疑问：直接返回的话，存在两个问题：1、结果怎么获取？2、后台运行可能会被中断？）
定义AIDL接口
在src目录下用Java语法定义.aidl后缀的接口文件，客户端和服务端都需要保存一份接口文件的拷贝。编译时，SDK会为aild文件在gen目录下生成IBinder接口。服务端实现这个接口，客户端绑定该服务，调用接口中的方法实现进程间通信。
创建AIDL实现的服务端，步骤如下：
- 创建*.aidl文件：定义接口
- 实现接口：SDK根据aidl文件生成AIDL接口，它包含一个名为Stub的抽象内部类，该类声明了所有aidl描述的方法，你必须在代码里继承该Stub类并实现里面定义的方法。
- 向客户端公开接口：继承Service，复写onBind方法，返回Stub的实现类。
注意：aidl文件一旦发布，注意客户端和服务端的接口兼容性，要改必须一起改。
1. 创建aidl文件
AIDL接口可以定义多个带入参和返回值的函数，参数和返回值可以是任意类型，甚至是其他AIDL接口
默认地，AIDL支持如下数据类型：
- Java语言的基本类型（int,long,char,boolean等）
- String
- CharSequence
- List
列表中的元素必须如下三种类型：AIDL支持的数据类型、其他AIDL生成的接口、自定义的可序列化类型，接收到的实际类型是ArrayList（？） - Map
类型要求与List相同，不支持Map，接收到的实际类型是HashMap
你需要import以上类型之外的其他类型，即使在同一个包中。
当定义服务接口时，需要注意：
- 方法可以由0或者多个参数，可以返回具体的值或者无返回值
- 所有非基础类型的参数必须指定参数方向：入参in 出参out inout， 默认是in
- 所有在aidl文件中的注释都会包含在自动生成的IBinder接口文件（除非注释在import和package之前）
- AIDL只支持方法，不支持变量
aidl例子代码：
// 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, 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); }
保存你的aidl文件在工程的src目录下，当你编译时，SDK工具会自动在gen目录下生成IBinder接口文件，生成的文件文件名与aidl文件一致，后缀是.java（IRemoteService.aidl对应IRemoteService.java）。
如果使用Eclipse，增量编译会立即自动生成java接口文件。如果你使用Ant工具，你需要使用ant debug或者ant release编译。
2. 实现接口
自动生成的java接口文件包含名为Stub的抽象子类（YourInterface.Stub）。
继承Stub类，实现里面的接口。
例子代码：
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 } };
mBinder是Stub的实例，为服务定义了远程调用接口。下一步，客户端通过mBinder调用服务。
实现AIDL接口，有如下规则：
- 线程安全，调用可能来自多个线程。
- 默认的，RPC是同步调用，如果服务需要花费较长时间才能完成处理，不建议在应用主线程中调用，否则会导致ANR。
- 服务不会抛任何一场给客户端
3. 暴露接口给客户端
继承Service，实现onBind，返回mBinder（Stub类），例子如下：
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 } }; }
当客户端调用bindService连接服务，客户端的onServiceConnected回调函数会受到mBinder实例，通过服务的onBind函数。
客户端和服务端在不同的应用时，客户端需要一份aidl文件的拷贝。
客户端接到IBinder的onServiceConnected回调，需要调用YourServiceInterface.Stub.asInterface(service)转换为YourServiceInterface类型。例子如下：
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; } };
通过IPC传递对象
自定义的类需要实现Parcelable接口，步骤如下：
- 实现Parcelable接口
- 实现writeToParcel，将当前类的状态写入Parcel
- 添加静态字段CREATOR，实现Parcelable.Creator
- 最后，创建AIDL文件声明这个可打包的类（见下文的Rect.aidl），如果使用的是自定义的编译过程，那么不要编译此AIDL文件，它像C语言的头文件一样不需要编译。
AIDL会使用这些方法的成员序列化和反序列化对象。下面的代码演示如何使Rect类支持序列化（parcelable）
package android.graphics; // Declare Rect so AIDL can find it and knows that it implements // the parcelable protocol. parcelable Rect;
下面的例子演示了如何让Rect类实现Parcelable协议。
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) { 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(); } }
调用IPC方法
这里给出调用远端AIDL接口的步骤：
1. 在 src/ 目录下包含.adil文件。
2. 声明一个IBinder接口（通过.aidl文件生成的）的实例。
3. 实现ServiceConnection.
4. 调用Context.bindService()绑定你的ServiceConnection实现类的对象（也就是远程服务端）。
5. 在onServiceConnected()方法中会接收到IBinder对象（也就是服务端），调用YourInterfaceName.Stub.asInterface((IBinder)service)将返回值转换为YourInterface类型。
6. 调用接口中定义的方法，并且应该总是捕获连接被打断时抛出的DeadObjectException异常，这是远端方法可能会抛出唯一异常。
7. 调用Context.unbindService()方法断开连接。
这里有几个关于调用IPC服务的提示：
- 对象是在进程间会进行引用计数
- 可以发送匿名对象作为方法的参数
更多关于服务绑定的内容请看Bound Services相关文档。
下面是AIDL-created服务的演示代码，该代码是从ApiDemos工程中的Remote Service中提取的。
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); } } }; }
翻译自：http://developer.android.com/guide/components/aidl.html
参考自：http://www.cnblogs.com/hibraincol/archive/2011/09/06/2169325.html（翻译的非常好）