Develop系列-API Guides-应用组件-Services-AIDL

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/article/5512673.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：/article/5851794.html（翻译的非常好）