AIDL (Android(安卓)Interface Definition Language) Android(安卓)接口定义语言

AIDL (Android Interface Definition Language) 是一种接口定义语言,用于生成代码允许Android设备上的两个进程间进程通信(IPC).
如果你需要编写一个进程(比如Activity)访问另一个进程(比如Services)的对象的方法代码,你可以使用AIDL自动生成代码而不用自己配置大量的参数.
AIDL IPC基于接口机制,类似COM,Corba,且更加轻量化.它使用一个代理来在客户和实现间传递值.

Implementing IPC Using AIDL 实现进程通信IPC

分为五个步骤:
1.创建 SomeService.aidl 文件
利用aidl.exe生成接口文件.若你的IDE安装了ADT,将会在gen目录或src相应包中自动根据描述文件生成同名接口文件.否则请手动:

命令行:
adil path\SomeService.adil <CR>

注意:
1.自定义类在aidl描述文件中,即便在同一个包中,也要显式import.
2.在aidl文件中所有非Java原始类型参数必须加上标记:in, out, inout.
3.Java 原始类型默认为in,且不能为其它.
4.Java 原始类型包括为java.lang, java,util包中包括的类.
5.接口名同aidl文件名.
6.接口前不用加访问权限修饰符public ,private, protected等,也不能用final ,static.

接口文件分析:

接口中生成一个Stub的抽象类,里面包括aidl定义的方法.还包括一些其它辅助方法.值得关注的是asInterface(IBinder iBinder),它返回接口的实例.

2.实现接口
接口的实现需继承接口.Stub.并实现Stub类的方法.
下面给出一个使用匿名方式实现的例子.

private final SomeService.Stub binder = new SomeService.Stub(){
public void service(){
//...
}
}

注意:
1.没有异常会正常返回
2.RPC通常比较耗时且是异步的,因此应该在线程中调用RPC服务.
3.只支持方法,不支持静态字段.

3.暴露接口给客户
客户要服务,当然要知道在哪有服务.通常一台服务器可能提供不止一个服务.因些,我们使用
RomoteService来管理所有远程服务.
暴露服务必须继承Service.并实现onBind()方法.

Java代码

public class RemoteService extends Service{
...
@Override
public IBinderonBind(Intentintent){
//Selecttheinterfacetoreturn.Ifyourserviceonlyimplements
//asingleinterface,youcanjustreturnitherewithoutchecking
//theIntent.
if (SomeService. class .getName().equals(intent.getAction())){
return mBinder;
}
if (ISecondary. class .getName().equals(intent.getAction())){
return mSecondaryBinder;
}
return null ;
}
/**
*TheSomeServiceInterfaceisdefinedthroughIDL
*/
private final SomeService.StubmBinder= new SomeService.Stub(){
public void registerCallback(SomeServiceCallbackcb){
if (cb!= null )mCallbacks.register(cb);
}
public void unregisterCallback(SomeServiceCallbackcb){
if (cb!= null )mCallbacks.unregister(cb);
}
};
/**
*Asecondaryinterfacetotheservice.
*/
private final ISecondary.StubmSecondaryBinder= new ISecondary.Stub(){
public int getPid(){
return Process.myPid();
}
public void basicTypes( int anInt, long aLong, boolean aBoolean,
float aFloat, double aDouble,StringaString){
}
};
}

public class RemoteService extends Service {...    @Override    public IBinder onBind(Intent intent) {        // Select the interface to return.  If your service only implements        // a single interface, you can just return it here without checking        // the Intent.        if (SomeService.class.getName().equals(intent.getAction())) {            return mBinder;        }        if (ISecondary.class.getName().equals(intent.getAction())) {            return mSecondaryBinder;        }        return null;    }    /**     * The SomeService Interface is defined through IDL     */    private final SomeService.Stub mBinder = new SomeService.Stub() {        public void registerCallback(SomeServiceCallback cb) {            if (cb != null) mCallbacks.register(cb);        }        public void unregisterCallback(SomeServiceCallback cb) {            if (cb != null) mCallbacks.unregister(cb);        }    };    /**     * A secondary interface to the service.     */    private final ISecondary.Stub mSecondaryBinder = new ISecondary.Stub() {        public int getPid() {            return Process.myPid();        }        public void basicTypes(int anInt, long aLong, boolean aBoolean,                float aFloat, double aDouble, String aString) {        }    };}

这样暴露好了服务,接着做什么?当然是调用服务了.

调用之前,有必要了解下对象打包,类似与Java的对象序列化.

4.使用打包传送参数

如果一个类要使用打包功能(类似对象序列化),要实现如下5个步骤:

4.1 实现 Parcelable接口
4.2 实现 public void writeToParcel(Parcel out) 方法
4.3 实现 public void readFromParcel(Parcel in) 方法
4.4 添加一个静态字段 CREATOR 到实现 Parcelable.Creator 接口的类中
4.5 创建一个aidl文件声明你的可打包的类

示例:
Rect.java

Java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= new Parcelable.Creator<Rect>(){
public RectcreateFromParcel(Parcelin){
return new Rect(in);
}
public Rect[]newArray( int size){
return new Rect[size];
}
};
public Rect(){
}
private Rect(Parcelin){
readFromParcel(in);
}
public void writeToParcel(Parcelout){
out.writeInt(left);
out.writeInt(top);
out.writeInt(right);
out.writeInt(bottom);
}
public void readFromParcel(Parcelin){
left=in.readInt();
top=in.readInt();
right=in.readInt();
bottom=in.readInt();
}
}

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();    }}

Rect.aidl

Java代码

package android.graphics;
//DeclareRectsoAIDLcanfinditandknowsthatitimplements
//theparcelableprotocol.
parcelableRect;

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

注意:
参数一定不能越界.

5.调用IPC方法
调用IPC方法还有6个步骤:
如果觉得烦,那就尽力弄懂,不然你不晕,我译得也晕..

5.1 声明aidl定义的接口类型引用
5.2 实现 ServiceConnection
5.3 调用 Context.bindService(),传入 ServiceConnection 的实现
5.4 在你的 ServiceConnection.onServiceConnected(),你将得到一个 IBinder 实例(service). 调用 YourInterfaceName.Stub.asInterface((IBinder)service)强制转换 YourInterface 类型.
5.5 调用接口定义的方法.你应该始终小心 DeadObjectException 异常,当连接不成功或中断它就会抛出,这也是远程对象唯一的一个异常.
5.6 断开连接,调用 Context.unbindService().

注解:
你可以使用匿名对象作为参数.
对象是引用计数.

ApiDemos 有个子the Remote Activity 的例子.

Java代码

public class RemoteServiceBinding extends Activity{
/**Theprimaryinterfacewewillbecallingontheservice.*/
IRemoteServicemService= null ;
/**Anotherinterfaceweuseontheservice.*/
ISecondarymSecondaryService= null ;
ButtonmKillButton;
TextViewmCallbackText;
private boolean mIsBound;
/**
*Standardinitializationofthisactivity.SetuptheUI,thenwait
*fortheusertopokeitbeforedoinganything.
*/
@Override
protected void onCreate(BundlesavedInstanceState){
super .onCreate(savedInstanceState);
setContentView(R.layout.remote_service_binding);
//Watchforbuttonclicks.
Buttonbutton=(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( "Notattached." );
}
/**
*Classforinteractingwiththemaininterfaceoftheservice.
*/
private ServiceConnectionmConnection= new ServiceConnection(){
public void onServiceConnected(ComponentNameclassName,
IBinderservice){
//Thisiscalledwhentheconnectionwiththeservicehasbeen
//established,givingustheserviceobjectwecanuseto
//interactwiththeservice.Wearecommunicatingwithour
//servicethroughanIDLinterface,sogetaclient-side
//representationofthatfromtherawserviceobject.
mService=IRemoteService.Stub.asInterface(service);
mKillButton.setEnabled( true );
mCallbackText.setText( "Attached." );
//Wewanttomonitortheserviceforaslongasweare
//connectedtoit.
try {
mService.registerCallback(mCallback);
} catch (RemoteExceptione){
//Inthiscasetheservicehascrashedbeforewecouldeven
//doanythingwithit;wecancountonsoonbeing
//disconnected(andthenreconnectedifitcanberestarted)
//sothereisnoneedtodoanythinghere.
}
//Aspartofthesample,telltheuserwhathappened.
Toast.makeText(RemoteServiceBinding. this ,R.string.remote_service_connected,
Toast.LENGTH_SHORT).show();
}
public void onServiceDisconnected(ComponentNameclassName){
//Thisiscalledwhentheconnectionwiththeservicehasbeen
//unexpectedlydisconnected--thatis,itsprocesscrashed.
mService= null ;
mKillButton.setEnabled( false );
mCallbackText.setText( "Disconnected." );
//Aspartofthesample,telltheuserwhathappened.
Toast.makeText(RemoteServiceBinding. this ,R.string.remote_service_disconnected,
Toast.LENGTH_SHORT).show();
}
};
/**
*Classforinteractingwiththesecondaryinterfaceoftheservice.
*/
private ServiceConnectionmSecondaryConnection= new ServiceConnection(){
public void onServiceConnected(ComponentNameclassName,
IBinderservice){
//Connectingtoasecondaryinterfaceisthesameasany
//otherinterface.
mSecondaryService=ISecondary.Stub.asInterface(service);
mKillButton.setEnabled( true );
}
public void onServiceDisconnected(ComponentNameclassName){
mSecondaryService= null ;
mKillButton.setEnabled( false );
}
};
private OnClickListenermBindListener= new OnClickListener(){
public void onClick(Viewv){
//Establishacoupleconnectionswiththeservice,binding
//byinterfacenames.Thisallowsotherapplicationstobe
//installedthatreplacetheremoteservicebyimplementing
//thesameinterface.
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 OnClickListenermUnbindListener= new OnClickListener(){
public void onClick(Viewv){
if (mIsBound){
//Ifwehavereceivedtheservice,andhenceregisteredwith
//it,thennowisthetimetounregister.
if (mService!= null ){
try {
mService.unregisterCallback(mCallback);
} catch (RemoteExceptione){
//Thereisnothingspecialweneedtodoiftheservice
//hascrashed.
}
}
//Detachourexistingconnection.
unbindService(mConnection);
unbindService(mSecondaryConnection);
mKillButton.setEnabled( false );
mIsBound= false ;
mCallbackText.setText( "Unbinding." );
}
}
};
private OnClickListenermKillListener= new OnClickListener(){
public void onClick(Viewv){
//Tokilltheprocesshostingourservice,weneedtoknowits
//PID.Convenientlyourservicehasacallthatwillreturn
//tousthatinformation.
if (mSecondaryService!= null ){
try {
int pid=mSecondaryService.getPid();
//Notethat,thoughthisAPIallowsustorequestto
//killanyprocessbasedonitsPID,thekernelwill
//stillimposestandardrestrictionsonwhichPIDsyou
//areactuallyabletokill.Typicallythismeansonly
//theprocessrunningyourapplicationandanyadditional
//processescreatedbythatappasshownhere;packages
//sharingacommonUIDwillalsobeabletokilleach
//other'sprocesses.
Process.killProcess(pid);
mCallbackText.setText( "Killedserviceprocess." );
} catch (RemoteExceptionex){
//Recovergracefullyfromtheprocesshostingthe
//serverdying.
//Justforpurposesofthesample,putupanotification.
Toast.makeText(RemoteServiceBinding. this ,
R.string.remote_call_failed,
Toast.LENGTH_SHORT).show();
}
}
}
};
//----------------------------------------------------------------------
//Codeshowinghowtodealwithcallbacks.
//----------------------------------------------------------------------
/**
*Thisimplementationisusedtoreceivecallbacksfromtheremote
*service.
*/
private IRemoteServiceCallbackmCallback= new IRemoteServiceCallback.Stub(){
/**
*Thisiscalledbytheremoteserviceregularlytotellusabout
*newvalues.NotethatIPCcallsaredispatchedthroughathread
*poolrunningineachprocess,sothecodeexecutingherewill
*NOTberunninginourmainthreadlikemostotherthings--so,
*toupdatetheUI,weneedtouseaHandlertohopoverthere.
*/
public void valueChanged( int value){
mHandler.sendMessage(mHandler.obtainMessage(BUMP_MSG,value, 0 ));
}
};
private static final int BUMP_MSG= 1 ;
private HandlermHandler= new Handler(){
@Override public void handleMessage(Messagemsg){
switch (msg.what){
case BUMP_MSG:
mCallbackText.setText( "Receivedfromservice:" +msg.arg1);
break ;
default :
super .handleMessage(msg);
}
}
};
}

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