为了简化我们实现Binder进程间通信的繁琐步骤,系统提供了AIDL文件,编译通过即可生成对应的java文件。承接上篇文章Android进程间通信-AIDL的简单使用 ,这里手动实现aidl自动生成的aidl文件,便于我们进一步理解内部的一些逻辑。
实现步骤
1 定义一个IOperation接口,并在内部声明一个供客户端跨进程调用的方法,并使该接口继承IInterface接口。
public interface IOperation extends IInterface {
/* Binder描述符 */
static final String DESCRIPTOR = "com.example.aidlmanualtest.IOperation";
/**
* 方法标识符 :规定了最小和最大范围
*
* The action to perform. This should be a number between
* {@link #FIRST_CALL_TRANSACTION}
* {@link #LAST_CALL_TRANSACTION}.
*
* 这段说明是在IBiner的transact()方法中
*/
static final int TRANSACTION_getSum = IBinder.FIRST_CALL_TRANSACTION + 0;
// 定义了一个供跨进程调用的方法
public double getSum(double first, double second) throws RemoteException;
}
2 跨进程方法调用的处理逻辑,主要集中在接口实现类Stub和Stub的代理Proxy类中
public class IOperationStub extends Binder implements IOperation {
public IOperationStub() {
/**
* Convenience method for associating a specific interface with the
* Binder. After calling, queryLocalInterface() will be implemented for
* you to return the given owner IInterface when the corresponding
* descriptor is requested.
*
* 将一个IInterface类型的接口实例与Binder关联起来,DESCRIPTOR相当于一个标识。当该方法被调用后,
* 可通过queryLocalInterface(DESCRIPTOR)获取与这个标识相应的接口实例
*/
this.attachInterface(this, DESCRIPTOR);
}
/**
* 用于将服务端的Binder对象转换成客户端需要的AIDL接口类型的对象区分进程:
* <p/>
* 客户端和服务端处于同一进程:直接返回服务端的Stub对象
* <p/>
* 客户端和服务端处于不同进程:返回封装好的Stub.proxy对象
*
* @param obj
* @return
*/
public static IOperation asInterface(IBinder obj) {
if (obj == null) {
return null;
}
/**
* Attempt to retrieve a local implementation of an interface for this
* Binder object. If null is returned, you will need to instantiate a
* proxy class to marshall calls through the transact() method.
*
* 尝试在本地检索实现了该接口的Binder对象实例
*/
android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
if (iin != null && (iin instanceof IOperation)) {
return ((IOperation) iin);
}
/**
* 假如本地检索返回为null,需要手动生成一个proxy代理类,并在其中通过transact() 方法去处理请求
*/
return new IOperationStub.Proxy(obj);
}
@Override
public IBinder asBinder() {
return this;
}
/**
* 该方法运行在服务端,当客户端发起请求,会进入到该方法进行处理
* <p/>
* code:用于标识客户端请求调用的目标方法(即在IOperation中定义的方法标识符)
* <p/>
* data:当请求的目标方法含有参数时,该参数封装了请求的参数
* <p/>
* reply:当请求需要返回结果时,该参数封装了处理结果
*/
@Override
protected boolean onTransact(int code, Parcel data, Parcel reply, int flags)
throws RemoteException {
// 通过code区分不同的方法调用
switch (code) {
case INTERFACE_TRANSACTION:
reply.writeString(DESCRIPTOR);
return true;
case TRANSACTION_getSum:
/**
* Read an IBinder interface token in the parcel at the current
* {@link #dataPosition}. This is used to validate that the
* marshalled transaction is intended for the target interface.
*/
data.enforceInterface(DESCRIPTOR);
// 通过data获取请求的参数
double first = data.readDouble();
double second = data.readDouble();
double result = this.getSum(first, second);
reply.writeNoException();
// 将结果写入到reply中
reply.writeDouble(result);
return true;
default:
break;
}
return super.onTransact(code, data, reply, flags);
}
@Override
public double getSum(double fisrt, double second) throws RemoteException {
return 0;
}
private static class Proxy implements IOperation {
private IBinder mRemote;
Proxy(IBinder mRemote) {
this.mRemote = mRemote;
}
@Override
public IBinder asBinder() {
return mRemote;
}
public java.lang.String getInterfaceDescriptor() {
return DESCRIPTOR;
}
@Override
public double getSum(double fisrt, double second)
throws RemoteException {
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
double result = 0;
try {
/**
* Store an IBinder interface token in the parcel at the current
* {@link #dataPosition}. This is used to validate that the
* marshalled transaction is intended for the target interface.
*/
data.writeInterfaceToken(DESCRIPTOR);
// 将请求的参数写入到data中
data.writeDouble(fisrt);
data.writeDouble(second);
// 调用transact()方法,发起跨进程请求,当前进程挂起
mRemote.transact(TRANSACTION_getSum, data, reply, 0);
// 从reply中获取返回的结果
reply.readException();
result = reply.readDouble();
} catch (Exception e) {
} finally {
data.recycle();
reply.recycle();
}
return result;
}
}
}
总结
总体逻辑:
1 客户端调用getSum()方法
2 将该方法需要的传递的参数写入到data中
3 调用transact()方法发起跨进程请求
4 服务端的onTransact()的方法被调用,客户端的进程被挂起
5 服务端返回结果,从reply中取出结果,并返回