下图简易描述了实现的原理:
假设A应用需要请求B应用的接口服务，以下是实现的流程:
1.根据请求的接口，首先识别请求的类型，然后构建该请求对应的Sender。Sender里面包含请求接口、请求的方法、参数和需要连接的IPCService类名。
public abstract class Sender implements ISender {
private long mTimeStamp;
/**
* 请求接口的类型
*/
private ObjectWrapper mObject;
/**
* 请求的方法
*/
private MethodWrapper mMethod;
/**
* 请求的参数
*/
private ParameterWrapper[] mParameters;
private Class<? extends IPCService> mService;
...
}
ObjectWrapper、MethodWrapper、ParameterWrapper都是包装类，继承Parcelable用于传输，里面详细描述了请求方法的类名或映射等详细信息。
2.Sender执行sender方法，获取请求的返回包装类Reply.
(1)Sender将所有Wrapper类打包放入Mail实体传给指定的IPCService。
public synchronized final Reply send(Method method, Object[] parameters) throws IPCException {
mTimeStamp = TimeStampGenerator.getTimeStamp();
if (parameters == null) {
parameters = new Object[0];
}
ParameterWrapper[] parameterWrappers = getParameterWrappers(method, parameters);
MethodWrapper methodWrapper = getMethodWrapper(method, parameterWrappers);
registerClass(method);
setParameterWrappers(parameterWrappers);
Mail mail = new Mail(mTimeStamp, mObject, methodWrapper, mParameters);
mMethod = methodWrapper;
return CHANNEL.send(mService, mail);
}
(2)IPCService定义了通用的AIDL接口。
public interface IIPCService extends IInterface {
/**
* 发送请求
*
* @param mail
* @return
* @throws RemoteException
*/
Reply send(Mail mail) throws RemoteException;
/**
* 注册回调
*
* @param callback
* @param pid
* @throws RemoteException
*/
void register(IIPCServiceCallback callback, int pid) throws RemoteException;
/**
* 资源回收
*
* @param timeStamps
* @throws RemoteException
*/
void gc(List<Long> timeStamps) throws RemoteException;
}
IPCService根据Mail中描述的请求类型，生成指定的Receiver来处理。
private final IIPCService.Stub mBinder = new IIPCService.Stub() {
@Override
public Reply send(Mail mail) {
try {
Receiver receiver = ReceiverDesignator.getReceiver(mail.getObject());
int pid = mail.getPid();
IIPCServiceCallback callback = mCallbacks.get(pid);
if (callback != null) {
receiver.setIPCServiceCallback(callback);
}
return receiver.action(mail.getTimeStamp(), mail.getMethod(), mail.getParameters());
} catch (IPCException e) {
e.printStackTrace();
return new Reply(e.getErrorCode(), e.getMessage());
}
}
@Override
public void register(IIPCServiceCallback callback, int pid) throws RemoteException {
mCallbacks.put(pid, callback);
}
@Override
public void gc(List<Long> timeStamps) throws RemoteException {
OBJECT_CENTER.deleteObjects(timeStamps);
}
};
(3)Receiver执行action方法，通过Wrapper信息，反射执行相对应的方法，返回结果Reply
/**
* 执行请求的方法，返回结果
*
* @param methodInvocationTimeStamp 方法执行的序号
* @param methodWrapper 请求的方法
* @param parameterWrappers 请求方法的参数
* @return
* @throws IPCException
*/
public final Reply action(long methodInvocationTimeStamp, MethodWrapper methodWrapper, ParameterWrapper[] parameterWrappers) throws IPCException {
setMethod(methodWrapper, parameterWrappers);
setParameters(methodInvocationTimeStamp, parameterWrappers);
Object result = invokeMethod();
if (result == null) {
return null;
} else {
return new Reply(new ParameterWrapper(result));
}
}
3.最后再通过动态代理IPCInvocationHandler，实现以上流程的动态执行。
public class IPCInvocationHandler implements InvocationHandler {
private Sender mSender;
public IPCInvocationHandler(Class<? extends IPCService> service, ObjectWrapper object) {
mSender = SenderDesignator.getPostOffice(service, SenderDesignator.TYPE_INVOKE_METHOD, object);
}
@Override
public Object invoke(Object proxy, Method method, Object[] objects) {
try {
Reply reply = mSender.send(method, objects);
if (reply == null) {
return null;
}
if (reply.success()) {
return reply.getResult();
} else {
IPCLog.e("Error occurs. Error " + reply.getErrorCode() + ": " + reply.getMessage());
return null;
}
} catch (IPCException e) {
e.printStackTrace();
IPCLog.e("Error occurs. Error " + e.getErrorCode() + ": " + e.getMessage());
return null;
}
}
}