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Camera App通過framework中Camera java類進(jìn)入jni部分，在android_hardware_Camera.cpp中：
android_hardware_Camera_native_setup()
{
sp<Camera> camera = Camera::connect();
}
這里調(diào)用Camera類的connect函數(shù)，返回一個(gè)Camera強(qiáng)指針。后續(xù)如startPreview, takePicture的動作均為對這個(gè)Camera對象的操作。
Camera::connect()，Camera.cpp
{
sp<Camera> c = new Camera();
const sp<ICameraService>& cs = getCameraService();
c->mCamera = cs->connect(c);
return c;
}
這里首先new一個(gè)Camera對象。getCameraService()會返回跨進(jìn)程的ICameraService，然后在其上調(diào)用connect：
Camera::getCameraService()
{
sp<IServiceManager> sm = defaultServiceManager();
sp<IBinder> binder;
binder = sm->getService(String16("media.camera"));
mCameraService = interface_cast<ICameraService>(binder);
return mCameraService;
}
首先取得跨進(jìn)程的IServiceManager，然后取得camera service（這個(gè)service在mediaserver啟動時(shí)注冊）。最重要的，把這個(gè)返回的binder對象經(jīng)過interface_cast<ICameraService>轉(zhuǎn)換，變成了BpCameraService類型:
IInterface.h:
template<typename INTERFACE>
inline sp<INTERFACE> interface_cast(const sp<IBinder>& obj)
{
return INTERFACE::asInterface(obj);
} sp<I##INTERFACE> I##INTERFACE::asInterface(const sp<IBinder>& obj) \
{ \
sp<I##INTERFACE> intr; \
if (obj != NULL) { \
intr = static_cast<I##INTERFACE*>( \
obj->queryLocalInterface( \
I##INTERFACE::descriptor).get()); \
if (intr == NULL) { \
intr = new Bp##INTERFACE(obj); \
} \
} \
return intr; \
} \ Camera::connect()中cs->connect(c)會調(diào)用到BpCameraService::connect(const sp<ICameraClient>& cameraClient)函數(shù)：
virtual sp<ICamera> connect(const sp<ICameraClient>& cameraClient)
{
Parcel data, reply;
data.writeInterfaceToken(ICameraService::getInterfaceDescriptor());
data.writeStrongBinder(cameraClient->asBinder());
remote()->transact(BnCameraService::CONNECT, data, &reply);
return interface_cast<ICamera>(reply.readStrongBinder());
}
這里會向remote((1))發(fā)起一個(gè)transaction，然后在reply中讀取binder，經(jīng)過interface_cast<ICamera>轉(zhuǎn)換為BpCamera類型。
類CameraService繼承了BnCameraService，而上面的remote實(shí)際為CameraService類型，因此實(shí)際上由CameraService::onTransact來處理CONNECT事務(wù)。
CameraService::onTransact()
{
BnCameraService::onTransact(code, data, reply, flags);
}
調(diào)用了父類BnCameraService的函數(shù)：
BnCameraService::onTransact()
{
sp<ICameraClient> cameraClient = interface_cast<ICameraClient>(data.readStrongBinder());
sp<ICamera> camera = connect(cameraClient);
reply->writeStrongBinder(camera->asBinder());
}
connect在BnCameraService中沒有實(shí)現(xiàn)，調(diào)用子類的connect：
sp<ICamera> CameraService::connect(const sp<ICameraClient>& cameraClient)
{
client = new Client(this, cameraClient, callingPid);
return client;
}
這里傳入了client的ICameraClient類型的cameraClient（保存在client的mCameraClient成員中），并向client返回了CameraService::Client對象，這樣可以實(shí)現(xiàn)client和server雙向調(diào)用。對于從CameraService到Camera的幀數(shù)據(jù)：
CameraService::Client::dataCallback()
{
sp<ICameraClient> c = client->mCameraClient;
c->dataCallbackTimestamp(timestamp, msgType, dataPtr);
}
這里調(diào)用Camera::dataCallbackTimestamp往Camera側(cè)發(fā)送數(shù)據(jù)。ICameraClient繼承關(guān)系：
class Camera : public BnCameraClient
Camera繼承BnCameraClient，表示Camera作為native端。另外，從Camera到CameraService端的調(diào)用是通過Camera類的sp<ICamera> mCamera成員實(shí)現(xiàn)的，具體調(diào)用下面會描述，相關(guān)類的繼承關(guān)系為：
class Client : public BnCamera
Client繼承BnCamera，表示Client作為Native端。
在Camera.cpp中，后續(xù)的startPreview等函數(shù)會在返回的BpCamera上操作。這樣, startPreview就進(jìn)入了BpCamera::startPreview：
status_t startPreview()
{
Parcel data, reply;
data.writeInterfaceToken(ICamera::getInterfaceDescriptor());
remote()->transact(START_PREVIEW, data, &reply);
return reply.readInt32();
}
這里會向遠(yuǎn)端發(fā)起一個(gè)START_PREVIEW的transaction。這個(gè)transaction會交給BnCamera處理（因?yàn)樽宇怌ameraService::Client沒有實(shí)現(xiàn)這個(gè)函數(shù)）：
BnCamera::onTransact()
{
case START_PREVIEW: {
LOGV("START_PREVIEW");
CHECK_INTERFACE(ICamera, data, reply);
reply->writeInt32(startPreview());
return NO_ERROR;
} break;
}
startPreview()進(jìn)入了子類CameraService::Client的startPreview():
status_t CameraService::Client::startPreview()
{
return startCameraMode(CAMERA_PREVIEW_MODE);
}
總結(jié)：
- Camera獲取CameraService
- 調(diào)用CameraService的connect，并傳入自身的Camera對象
- CameraService::onTransact處理CONNECT請求
- CameraService將傳入的Camera對象保存在Client類的mCameraClient成員中，并向Camera返回Client類對象
- 若有數(shù)據(jù)從CameraService到Camera，CameraService由mCameraClient呼叫Camera類的data callback
- 若有命令請求從Camera到CameraService, Camera調(diào)用CameraService::Client的相關(guān)函數(shù)
(1) remote()是什么？
remote()返回的是BpRefBase類的mRemote成員。在Binder.cpp中BpRefBase的構(gòu)造函數(shù)中，mRemote被初始化為IBinder指針：
BpRefBase::BpRefBase(const sp<IBinder>& o)
: mRemote(o.get()), mRefs(NULL), mState(0)
{
}
在Camera.cpp中獲取ICameraService時(shí)，
Camera::getCameraService()
{
sp<IBinder> binder;
binder = sm->getService(String16("media.camera"));
mCameraService = interface_cast<ICameraService>(binder);
}
getService返回的binder被傳入。interface_cast<ICameraService>會調(diào)用ICameraService::asInterface(const sp<IBinder>& obj)：
sp<I##INTERFACE> I##INTERFACE::asInterface(const sp<IBinder>& obj) \
{ \
sp<I##INTERFACE> intr; \
if (obj != NULL) { \
intr = static_cast<I##INTERFACE*>( \
obj->queryLocalInterface( \
I##INTERFACE::descriptor).get()); \
if (intr == NULL) { \
intr = new Bp##INTERFACE(obj); \
} \
} \
return intr; \
}
這里會觸發(fā)調(diào)用new BpCameraService(obj), obj為binder類型。
BpCameraService(const sp<IBinder>& impl)
: BpInterface<ICameraService>(impl)
{
}
進(jìn)入BpInterface的構(gòu)造函數(shù)。
template<typename INTERFACE>
inline BpInterface<INTERFACE>::BpInterface(const sp<IBinder>& remote)
: BpRefBase(remote)
{
}
調(diào)用BpRefBase的構(gòu)造函數(shù)。因此，remote()實(shí)際上就是getService返回的binder。
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