关于servicemanager的设计：
还是这张结构图，由于ProcessState & IPCThreadState是与binder deriver交互的，
所以对于client端来说BpBinder以下的部分是透明的。
我们从Activity的getsystemservice来一步步分析整个servicemanager提供服务的过程。
在contextImple.java 中
registerService(ALARM_SERVICE, new ServiceFetcher() {
public Object createService(ContextImpl ctx) {
IBinder b = ServiceManager.getService(ALARM_SERVICE);
IAlarmManager service = IAlarmManager.Stub.asInterface(b);
return new AlarmManager(service, ctx);
}});
注册的代码是static block的形式。
@Override
public Object getSystemService(String name) {
ServiceFetcher fetcher = SYSTEM_SERVICE_MAP.get(name);
return fetcher == null ? null : fetcher.getService(this);
}
getservice：
public Object getService(ContextImpl ctx) {
ArrayList<Object> cache = ctx.mServiceCache;
Object service;
synchronized (cache) {
if (cache.size() == 0) {
// Initialize the cache vector on first access.
// At this point sNextPerContextServiceCacheIndex
// is the number of potential services that are
// cached per-Context.
for (int i = 0; i < sNextPerContextServiceCacheIndex; i++) {
cache.add(null);
}
} else {
service = cache.get(mContextCacheIndex);
if (service != null) {
return service;
}
}
service = createService(ctx);
cache.set(mContextCacheIndex, service);
return service;
}
}
所以可以看到最终调用就是注册函数的内容
IBinder b = ServiceManager.getService(ALARM_SERVICE);
ServiceManager.java:
public static IBinder getService(String name) {
try {
IBinder service = sCache.get(name);
if (service != null) {
return service;
} else {
return getIServiceManager().getService(name);
}
} catch (RemoteException e) {
Log.e(TAG, "error in getService", e);
}
return null;
}
我们应用层看到的service对象是IBinder。
然后我们看看IServiceManager
private static IServiceManager getIServiceManager() {
if (sServiceManager != null) {
return sServiceManager;
}
// Find the service manager
sServiceManager = ServiceManagerNative.asInterface(BinderInternal.getContextObject());
return sServiceManager;
}
/**
* Return the global "context object" of the system. This is usually
* an implementation of IServiceManager, which you can use to find
* other services.
*/
public static final native IBinder getContextObject();
getContextObject
可以看到注释说明，返回的就是全局唯一的ServiceManager对象。
class ServiceManagerProxy implements IServiceManager {
public ServiceManagerProxy(IBinder remote) {
mRemote = remote;
}
public IBinder asBinder() {
return mRemote;
}
public IBinder getService(String name) throws RemoteException {
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IServiceManager.descriptor);
data.writeString(name);
mRemote.transact(GET_SERVICE_TRANSACTION, data, reply, 0);
IBinder binder = reply.readStrongBinder();
reply.recycle();
data.recycle();
return binder;
}
AIDL的实现：
网上有很多关于AIDL的讨论，解释等等。
AIDL是什么？
Android Interface definition language:
所以aidl是google为了便利的实现binder机制，而创建的一种语言。
AIDL的目的是为了便于开发者可以快速书写创建进程间通信的一种语言，或者代码。
package com.htc.globalsearch.imagesearch.service.aidl;
import com.htc.globalsearch.imagesearch.service.aidl.PersonImageItem;
import com.htc.globalsearch.imagesearch.service.aidl.ICallBack; interface IBuildService{
int getServiceStatus();
int findPerson(String path,int filter);
void registerCallback(ICallBack cb);
void unregisterCallback(ICallBack cb);
}
看看生成后变成什么？
/*
* This file is auto-generated. DO NOT MODIFY.
* Original file: D:\\AndroidDev\\github\\Example\\Examples\\ImageSearch\\src\\com\\htc\\globalsearch\\imagesearch\\service\\aidl\\IBuildService.aidl
*/
package com.htc.globalsearch.imagesearch.service.aidl;
public interface IBuildService extends android.os.IInterface
{
/** Local-side IPC implementation stub class. */
public static abstract class Stub extends android.os.Binder implements com.htc.globalsearch.imagesearch.service.aidl.IBuildService
{
private static final java.lang.String DESCRIPTOR = "com.htc.globalsearch.imagesearch.service.aidl.IBuildService";
/** Construct the stub at attach it to the interface. */
public Stub()
{
this.attachInterface(this, DESCRIPTOR);
}
/**
* Cast an IBinder object into an com.htc.globalsearch.imagesearch.service.aidl.IBuildService interface,
* generating a proxy if needed.
*/
public static com.htc.globalsearch.imagesearch.service.aidl.IBuildService asInterface(android.os.IBinder obj)
{
if ((obj==null)) {
return null;
}
android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
if (((iin!=null)&&(iin instanceof com.htc.globalsearch.imagesearch.service.aidl.IBuildService))) {
return ((com.htc.globalsearch.imagesearch.service.aidl.IBuildService)iin);
}
return new com.htc.globalsearch.imagesearch.service.aidl.IBuildService.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_getServiceStatus:
{
data.enforceInterface(DESCRIPTOR);
int _result = this.getServiceStatus();
reply.writeNoException();
reply.writeInt(_result);
return true;
}
case TRANSACTION_findPerson:
{
data.enforceInterface(DESCRIPTOR);
java.lang.String _arg0;
_arg0 = data.readString();
int _arg1;
_arg1 = data.readInt();
int _result = this.findPerson(_arg0, _arg1);
reply.writeNoException();
reply.writeInt(_result);
return true;
}
case TRANSACTION_registerCallback:
{
data.enforceInterface(DESCRIPTOR);
com.htc.globalsearch.imagesearch.service.aidl.ICallBack _arg0;
_arg0 = com.htc.globalsearch.imagesearch.service.aidl.ICallBack.Stub.asInterface(data.readStrongBinder());
this.registerCallback(_arg0);
reply.writeNoException();
return true;
}
case TRANSACTION_unregisterCallback:
{
data.enforceInterface(DESCRIPTOR);
com.htc.globalsearch.imagesearch.service.aidl.ICallBack _arg0;
_arg0 = com.htc.globalsearch.imagesearch.service.aidl.ICallBack.Stub.asInterface(data.readStrongBinder());
this.unregisterCallback(_arg0);
reply.writeNoException();
return true;
}
}
return super.onTransact(code, data, reply, flags);
}
private static class Proxy implements com.htc.globalsearch.imagesearch.service.aidl.IBuildService
{
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 int getServiceStatus() 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);
mRemote.transact(Stub.TRANSACTION_getServiceStatus, _data, _reply, 0);
_reply.readException();
_result = _reply.readInt();
}
finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
@Override public int findPerson(java.lang.String path, int filter) 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(path);
_data.writeInt(filter);
mRemote.transact(Stub.TRANSACTION_findPerson, _data, _reply, 0);
_reply.readException();
_result = _reply.readInt();
}
finally {
_reply.recycle();
_data.recycle();
}
return _result;
}
@Override public void registerCallback(com.htc.globalsearch.imagesearch.service.aidl.ICallBack cb) 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((((cb!=null))?(cb.asBinder()):(null)));
mRemote.transact(Stub.TRANSACTION_registerCallback, _data, _reply, 0);
_reply.readException();
}
finally {
_reply.recycle();
_data.recycle();
}
}
@Override public void unregisterCallback(com.htc.globalsearch.imagesearch.service.aidl.ICallBack cb) 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((((cb!=null))?(cb.asBinder()):(null)));
mRemote.transact(Stub.TRANSACTION_unregisterCallback, _data, _reply, 0);
_reply.readException();
}
finally {
_reply.recycle();
_data.recycle();
}
}
}
static final int TRANSACTION_getServiceStatus = (android.os.IBinder.FIRST_CALL_TRANSACTION + 0);
static final int TRANSACTION_findPerson = (android.os.IBinder.FIRST_CALL_TRANSACTION + 1);
static final int TRANSACTION_registerCallback = (android.os.IBinder.FIRST_CALL_TRANSACTION + 2);
static final int TRANSACTION_unregisterCallback = (android.os.IBinder.FIRST_CALL_TRANSACTION + 3);
}
public int getServiceStatus() throws android.os.RemoteException;
public int findPerson(java.lang.String path, int filter) throws android.os.RemoteException;
public void registerCallback(com.htc.globalsearch.imagesearch.service.aidl.ICallBack cb) throws android.os.RemoteException;
public void unregisterCallback(com.htc.globalsearch.imagesearch.service.aidl.ICallBack cb) throws android.os.RemoteException;
}
IBuildService.java
public static abstract class Stub extends android.os.Binder implements com.htc.globalsearch.imagesearch.service.aidl.IBuildService
关键是这个class，stub继承自binder，而且实现了IbuildService的接口。
在看service
private class ImageSearchBuildServiceImpl extends IBuildService.Stub{
所以，service是实现了Stub的内容，进而可以实现这个方法。
而service的onbind就是返回这个stub
@Override
public IBinder onBind(Intent intent) {
mCurrentCookie = intent.getLongExtra("cookie",-1);
Log.i(TAG, "[onBind] mCurrentCookie:"+mCurrentCookie);
iServiceImpl = new ImageSearchBuildServiceImpl(mImageSearchOperator);
return iServiceImpl;
}
通过bindservice，会把这个Ibinder对象返回给client端。