【移动应用开发技术】深入分析AIDL原理

【移动应用开发技术】深入分析AIDL原理

在上一篇文章（Service使用方式）中，介绍了Android进程间通信（IPC）的使用，并给出了一个示例。但并没有深入分析aidl是怎样可以做到进程间通信的，它的执行过程是怎样的？这篇文章来分析IRemoteService.aidl的执行过程，并理解aidl是怎样跨进程通信的。

当我们创建IRemoteService.aidl文件时，IDE会为我们在gen目录中创建相应的文件。[java]

viewplaincopy/**

This

file

is

auto-generated.

DO

NOT

MODIFY.

*

Original

file:

F:\\workspace\\AndroidImprove\\src\\com\\example\\aidl\\IRemoteService.aidl

*/

package

com.example.aidl;

public

interface

IRemoteService

extends

android.os.IInterface

{

/**

Local-side

IPC

implementation

stub

class.

*/

public

static

abstract

class

Stub

extends

android.os.Binder

implements

com.example.aidl.IRemoteService

{

private

static

final

java.lang.String

DESCRIPTOR

=

"com.example.aidl.IRemoteService";

/**

Construct

the

stub

at

attach

it

to

the

interface.

*/

public

Stub()

{

this.attachInterface(this,

DESCRIPTOR);

}

/**

*

Cast

an

IBinder

object

into

an

com.example.aidl.IRemoteService

interface,

*

generating

a

proxy

if

needed.

*/

public

static

com.example.aidl.IRemoteService

asInterface(android.os.IBinder

obj)

{

if

((obj==null))

{

return

null;

}

android.os.IInterface

iin

=

(android.os.IInterface)obj.queryLocalInterface(DESCRIPTOR);

if

(((iin!=null)&&(iin

instanceof

com.example.aidl.IRemoteService)))

{

return

((com.example.aidl.IRemoteService)iin);

}

return

new

com.example.aidl.IRemoteService.Stub.Proxy(obj);

}

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_register:

{

data.enforceInterface(DESCRIPTOR);

com.example.aidl.IRemoteCallback

_arg0;

_arg0

=

com.example.aidl.IRemoteCallback.Stub.asInterface(data.readStrongBinder());

this.register(_arg0);

reply.writeNoException();

return

true;

}

case

TRANSACTION_unregister:

{

data.enforceInterface(DESCRIPTOR);

com.example.aidl.IRemoteCallback

_arg0;

_arg0

=

com.example.aidl.IRemoteCallback.Stub.asInterface(data.readStrongBinder());

this.unregister(_arg0);

reply.writeNoException();

return

true;

}

case

TRANSACTION_execute:

{

data.enforceInterface(DESCRIPTOR);

this.execute();

reply.writeNoException();

return

true;

}

case

TRANSACTION_getStatus:

{

data.enforceInterface(DESCRIPTOR);

java.lang.String

_arg0;

_arg0

=

data.readString();

int

_result

=

this.getStatus(_arg0);

reply.writeNoException();

reply.writeInt(_result);

return

true;

}

}

return

super.onTransact(code,

data,

reply,

flags);

}

private

static

class

Proxy

implements

com.example.aidl.IRemoteService

{

private

android.os.IBinder

mRemote;

Proxy(android.os.IBinder

remote)

{

mRemote

=

remote;

}

public

android.os.IBinder

asBinder()

{

return

mRemote;

}

public

java.lang.String

getInterfaceDescriptor()

{

return

DESCRIPTOR;

}

//注册回调

public

void

register(com.example.aidl.IRemoteCallback

callback)

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.writeStrongBinder((((callback!=null))?(callback.asBinder()):(null)));

mRemote.transact(Stub.TRANSACTION_register,

_data,

_reply,

0);

_reply.readException();

}

finally

{

_reply.recycle();

_data.recycle();

}

}

//取消注册回调

public

void

unregister(com.example.aidl.IRemoteCallback

callback)

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.writeStrongBinder((((callback!=null))?(callback.asBinder()):(null)));

mRemote.transact(Stub.TRANSACTION_unregister,

_data,

_reply,

0);

_reply.readException();

}

finally

{

_reply.recycle();

_data.recycle();

}

}

//执行回调

public

void

execute()

throws

android.os.RemoteException

{

android.os.Parcel

_data

=

android.os.Parcel.obtain();

android.os.Parcel

_reply

=

android.os.Parcel.obtain();

try

{

_data.writeInterfaceToken(DESCRIPTOR);

mRemote.transact(Stub.TRANSACTION_execute,

_data,

_reply,

0);

_reply.readException();

}

finally

{

_reply.recycle();

_data.recycle();

}

}

//获取状态

public

int

getStatus(java.lang.String

flag)

throws

android.os.RemoteException

{

android.os.Parcel

_data

=

android.os.Parcel.obtain();

android.os.Parcel

_reply

=

android.os.Parcel.obtain();

int

_result;

try

{

_data.writeInterfaceToken(DESCRIPTOR);

_data.writeString(flag);

mRemote.transact(Stub.TRANSACTION_getStatus,

_data,

_reply,

0);

_reply.readException();

_result

=

_reply.readInt();

}

finally

{

_reply.recycle();

_data.recycle();

}

return

_result;

}

}

static

final

int

TRANSACTION_register

=

(android.os.IBinder.FIRST_CALL_TRANSACTION

+

0);

static

final

int

TRANSACTION_unregister

=

(android.os.IBinder.FIRST_CALL_TRANSACTION

+

1);

static

final

int

TRANSACTION_execute

=

(android.os.IBinder.FIRST_CALL_TRANSACTION

+

2);

static

final

int

TRANSACTION_getStatus

=

(android.os.IBinder.FIRST_CALL_TRANSACTION

+

3);

}

//注册回调

public

void

register(com.example.aidl.IRemoteCallback

callback)

throws

android.os.RemoteException;

//取消注册回调

public

void

unregister(com.example.aidl.IRemoteCallback

callback)

throws

android.os.RemoteException;

//执行回调

public

void

execute()

throws

android.os.RemoteException;

//获取状态

public

int

getStatus(java.lang.String

flag)

throws

android.os.RemoteException;

}

在ClientActivity绑定远程Service并建立连接时会调用ServiceConnection.onServiceConnected(ComponentNamename,IBinderservice)[java]

viewplaincopypublic

void

onServiceConnected(ComponentName

name,

IBinder

service)

{

remoteService

=

IRemoteService.Stub.asInterface(service);

//注册回调

try

{

remoteService.register(remoteCallback);

}

catch

(RemoteException

e)

{

e.printStackTrace();

}

}

IBinderservice是从RemoteService返回的IRemoteService.StubiBinder，这个对象是Server应用进程中的对象。IRemoteService.Stub.asInterface(service)在本地创建了一个代理

publicstaticcom.example.aidl.IRemoteServiceasInterface(android.os.IBinderobj){if((obj==null)){returnnull;}android.os.IInterfaceiin=(android.os.IInterface)obj.queryLocalInterface(DESCRIPTOR);//这里肯定返回nullif(((iin!=null)&&(iininstanceofcom.example.aidl.IRemoteService))){return((com.example.aidl.IRemoteService)iin);}returnnewcom.example.aidl.IRemoteService.Stub.Proxy(obj);//创建一个本地代理}

当使用remoteService调用方法时，其实是调用了本地com.example.aidl.IRemoteService.Stub.Proxy对象的方法，从Proxy方法中可以看到，每个方法都执行了mRemote.transact(Stub.TRANSACTION_xxx,_data,_reply,0);。如：[java]

viewplaincopy//获取状态

public

int

getStatus(java.lang.String

flag)

throws

android.os.RemoteException

{

android.os.Parcel

_data

=

android.os.Parcel.obtain();

android.os.Parcel

_reply

=

android.os.Parcel.obtain();

int

_result;

try

{

_data.writeInterfaceToken(DESCRIPTOR);

_data.writeString(flag);

mRemote.transact(Stub.TRANSACTION_getStatus,

_data,

_reply,

0);

_reply.readException();

_result

=

_reply.readInt();

}

finally

{

_reply.recycle();

_data.recycle();

}

return

_result;

}

这一过程是把Client端的参数转换成Parcel（_data）传递到Server端，而在Server端又会把返回数据保存到_reply中，这就形成了一次交互。mRemote是远程对象，transact方法会执行onTransact方法[java]

viewplaincopypublic

final

boolean

transact(int

code,

Par