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Android中AIDL详解
介绍
Android Interface Definition Language (AIDL)， Android接口定义语言。系统中的进程之间不能共享内存，因此，需要提供一些机制在不同进程之间进行数据通信Interprocess communication (IPC)。AIDL就是解决这个问题的。
阅读本文需要了解Service的相关知识
创建.aidl文件
aidl是用Java语法编写的，后缀为.aidl的文件。
每一个aidl文件必须定义一个接口，在这个接口里声明方法 在aidl里不能有static属性（field） aidl支持基本的数据类型，当你需要使用额外的数据类型时需要把它们import进来，即使它们跟这个文件在同一个包中。示例
// 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);
}
把aidl文件存在src/目录下，当你build项目的时候，SDK工具会在gen/目录下生成一个与.aidl文件名字相同的.java文件。
实现接口
生成的IRemoteService.java如下
public interface IRemoteService extends android.os.IInterface
{
/** Local-side IPC implementation stub class. */
public static abstract class Stub extends android.os.Binder implements com.spark.meizi.IRemoteService
{
private static final java.lang.String DESCRIPTOR = "com.spark.meizi.IRemoteService";
/** Construct the stub at attach it to the interface. */
public Stub()
{
this.attachInterface(this, DESCRIPTOR);
}
/**
* Cast an IBinder object into an com.spark.meizi.IRemoteService interface,
* generating a proxy if needed.
*/
public static com.spark.meizi.IRemoteService asInterface(android.os.IBinder obj)
{
if ((obj==null)) {
return null;
}
android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
if (((iin!=null)&&(iin instanceof com.spark.meizi.IRemoteService))) {
return ((com.spark.meizi.IRemoteService)iin);
}
return new com.spark.meizi.IRemoteService.Stub.Proxy(obj);
}
@Override public android.os.IBinder asBinder()
{
return this;
}
@Override public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException
{
switch (code)
{
case INTERFACE_TRANSACTION:
{
reply.writeString(DESCRIPTOR);
return true;
}
case TRANSACTION_basicTypes:
{
data.enforceInterface(DESCRIPTOR);
int _arg0;
_arg0 = data.readInt();
long _arg1;
_arg1 = data.readLong();
boolean _arg2;
_arg2 = (0!=data.readInt());
float _arg3;
_arg3 = data.readFloat();
double _arg4;
_arg4 = data.readDouble();
java.lang.String _arg5;
_arg5 = data.readString();
this.basicTypes(_arg0, _arg1, _arg2, _arg3, _arg4, _arg5);
reply.writeNoException();
return true;
}
}
return super.onTransact(code, data, reply, flags);
}
private static class Proxy implements com.spark.meizi.IRemoteService
{
private android.os.IBinder mRemote;
Proxy(android.os.IBinder remote)
{
mRemote = remote;
}
@Override public android.os.IBinder asBinder()
{
return mRemote;
}
public java.lang.String getInterfaceDescriptor()
{
return DESCRIPTOR;
}
/**
* Demonstrates some basic types that you can use as parameters
* and return values in AIDL.
*/
@Override public void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, java.lang.String aString) throws android.os.RemoteException
{
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
try {
_data.writeInterfaceToken(DESCRIPTOR);
_data.writeInt(anInt);
_data.writeLong(aLong);
_data.writeInt(((aBoolean)?(1):(0)));
_data.writeFloat(aFloat);
_data.writeDouble(aDouble);
_data.writeString(aString);
mRemote.transact(Stub.TRANSACTION_basicTypes, _data, _reply, 0);
_reply.readException();
}
finally {
_reply.recycle();
_data.recycle();
}
}
}
static final int TRANSACTION_basicTypes = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
}
/**
* Demonstrates some basic types that you can use as parameters
* and return values in AIDL.
*/
public void basicTypes(int anInt, long aLong, boolean aBoolean, float aFloat, double aDouble, java.lang.String aString) throws android.os.RemoteException;
}
在这个文件中有一个内部类Stub，这是父接口的一个抽象实现，并声明了aidl中的所有方法。为了实现由aidl生成的接口，我们需要继承Stub并实现从aidl继承过来的方法。下面是一个使用匿名类的例子
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
}
};
这样mBinder就是一个Stub的实例了，下一步就是如何在client端使用，与service端产生交互了。
注：
在Client中使用接口
当你已经实现你的Service之后，你需把它暴露在Client中使Client可以绑定它。继承Service并实现onBind()方法，来返回一个实现了Stub的实例。下面就是一个把IRemoteService暴露给Client的例子：
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
}
};
}
现在client（比如是一个Activity）可以调用bindService()来连接这个Service，通过onServiceConnected()来接收Service中 onBind() 返回的mBinder，最后使用YourServiceInterface.Stub.asInterface(service)来把返回的mBinder转换成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;
}
};
注：
如果Service和Client在两个不同的Application中，Client的Application的src/目录下必须也有对应的.aidl文件。
一个Client的例子
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.
*/