Android中跨进程通信方式之使用AIDL进阶篇
本文分析上一篇《Android中跨进程通信方式之使用AIDL》中IUserManager的内部结构。
package com.example.aidl;
public interface IUserManager extends android.os.IInterface {
/** Local-side IPC implementation stub class. */
public static abstract class Stub extends android.os.Binder implements com.example.aidl.IUserManager {
private static final java.lang.String DESCRIPTOR = "com.example.aidl.IUserManager";
/** Construct the stub at attach it to the interface. */
public Stub() {
this.attachInterface(this, DESCRIPTOR);
}
/** * Cast an IBinder object into an com.example.aidl.IUserManager * interface, generating a proxy if needed. */
public static com.example.aidl.IUserManager asInterface(
android.os.IBinder obj) {
if ((obj == null)) {
return null;
}
android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
if (((iin != null) && (iin instanceof com.example.aidl.IUserManager))) {
return ((com.example.aidl.IUserManager) iin);
}
return new com.example.aidl.IUserManager.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_findUser: {
data.enforceInterface(DESCRIPTOR);
java.util.List<com.example.aidl.User> _result = this.findUser();
reply.writeNoException();
reply.writeTypedList(_result);
return true;
}
case TRANSACTION_addUser: {
data.enforceInterface(DESCRIPTOR);
com.example.aidl.User _arg0;
if ((0 != data.readInt())) {
_arg0 = com.example.aidl.User.CREATOR
.createFromParcel(data);
} else {
_arg0 = null;
}
this.addUser(_arg0);
reply.writeNoException();
return true;
}
}
return super.onTransact(code, data, reply, flags);
}
private static class Proxy implements com.example.aidl.IUserManager {
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;
}
@Override
public java.util.List<com.example.aidl.User> findUser()
throws android.os.RemoteException {
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
java.util.List<com.example.aidl.User> _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
mRemote.transact(Stub.TRANSACTION_findUser, _data, _reply,
0);
_reply.readException();
_result = _reply
.createTypedArrayList(com.example.aidl.User.CREATOR);
} finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
@Override
public void addUser(com.example.aidl.User user)
throws android.os.RemoteException {
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
try {
_data.writeInterfaceToken(DESCRIPTOR);
if ((user != null)) {
_data.writeInt(1);
user.writeToParcel(_data, 0);
} else {
_data.writeInt(0);
}
mRemote.transact(Stub.TRANSACTION_addUser, _data, _reply, 0);
_reply.readException();
} finally {
_reply.recycle();
_data.recycle();
}
}
}
static final int TRANSACTION_findUser = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
static final int TRANSACTION_addUser = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1);
}
public java.util.List<com.example.aidl.User> findUser()
throws android.os.RemoteException;
public void addUser(com.example.aidl.User user)
throws android.os.RemoteException;
}
首先IUserManager继承IInterface，IInterface是远程AIDL需要继承的类。
具体AIDL是通过内部类Stub实现的，继承了Binder。
public static abstract class Stub extends android.os.Binder implements com.example.aidl.IUserManagerDESCRIPTOR是描述符，必须是包名+类名
private static final java.lang.String DESCRIPTOR = "com.example.aidl.IUserManager";将IBinder对象转换成IUserManager接口，如果不在一个进程，那么会转换成它的代理。
/** * Cast an IBinder object into an com.example.aidl.IUserManager * interface, generating a proxy if needed. */
public static com.example.aidl.IUserManager asInterface(
android.os.IBinder obj) {
if ((obj == null)) {
return null;
}
android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
if (((iin != null) && (iin instanceof com.example.aidl.IUserManager))) {
return ((com.example.aidl.IUserManager) iin);
}
return new com.example.aidl.IUserManager.Stub.Proxy(obj);
}onTransact是服务端最终执行的方法，根据code判断是执行接口中的哪个方法。从data中写入参数，将执行结果通过reply返回。
onTransact方法运行在服务端的Binder线程池中。
@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_findUser: {
data.enforceInterface(DESCRIPTOR);
java.util.List<com.example.aidl.User> _result = this.findUser();
reply.writeNoException();
reply.writeTypedList(_result);
return true;
}
case TRANSACTION_addUser: {
data.enforceInterface(DESCRIPTOR);
com.example.aidl.User _arg0;
if ((0 != data.readInt())) {
_arg0 = com.example.aidl.User.CREATOR
.createFromParcel(data);
} else {
_arg0 = null;
}
this.addUser(_arg0);
reply.writeNoException();
return true;
}
}
return super.onTransact(code, data, reply, flags);
}代理类Proxy，如果客户端与服务端不在一个进程中，那么代理类会工作。
private static class Proxy implements com.example.aidl.IUserManager这两个方法是客户端调用的。从data中写入参数，客户端调用transact方法，客户端当前线程挂起，该方法会执行服务端onTransact方法，等待服务端运行结束，将执行结果通过reply返回，客户端线程才继续执行。
@Override
public java.util.List<com.example.aidl.User> findUser()
throws android.os.RemoteException {
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
java.util.List<com.example.aidl.User> _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
mRemote.transact(Stub.TRANSACTION_findUser, _data, _reply,
0);
_reply.readException();
_result = _reply
.createTypedArrayList(com.example.aidl.User.CREATOR);
} finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
@Override
public void addUser(com.example.aidl.User user)
throws android.os.RemoteException {
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
try {
_data.writeInterfaceToken(DESCRIPTOR);
if ((user != null)) {
_data.writeInt(1);
user.writeToParcel(_data, 0);
} else {
_data.writeInt(0);
}
mRemote.transact(Stub.TRANSACTION_addUser, _data, _reply, 0);
_reply.readException();
} finally {
_reply.recycle();
_data.recycle();
}
}方法的code值
static final int TRANSACTION_findUser = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
static final int TRANSACTION_addUser = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1);IUserManager两个需要实现的抽象方法
public java.util.List<com.example.aidl.User> findUser()
throws android.os.RemoteException;
public void addUser(com.example.aidl.User user)
throws android.os.RemoteException;总结：当客户端跨进程请求服务端时，客户端当前线程会被挂起（transact方法执行，调用服务端onTransact方法），直到服务端返回数据才会继续执行，如果服务端是一个耗时的方法，那么客户端需要在子线程中请求，服务端的方法是运行在Binder线程池中的，所以不需要在用子线程去执行它。