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1）应用层处于整个框架的顶端，承担着于用户直接进行交互的责任，承接来自用户直接或者间接的比如预览/拍照/录像等一系列具体需求，一旦接收到用户相关UI操作，便会通过Camera Api v2标准接口将需求发送至Camera Framework部分，并且等待Camera Framework回传处理结果，其中包括了图像数据以及整体相机系统状态参数，之后将结果以一定方式反馈给用户，达到记录显示种种美好瞬间的目的。

2）Framework层主要位于Camera App与Camera Service之间，以jar包的形式运行在App进程中，它封装了Camera api v2接口的实现细节，暴露接口给App进行调用，进而接收来自App的请求，同时维护着请求在内部流转的业务逻辑，最终通过调用Camera AIDL跨进程接口将请求发送至Camera Service中进行处理，紧接着，等待Camera Service结果的回传，进而将最终结果发送至App

一、调用逻辑图

二、Framework的调用逻辑

（1）openCamera

最初的入口就是 CameraManager 的 openCamera 方法。AP层通过 api 标准接口将需求发送至Camera Framework。通过AIDl连接相机设备，将 CameraDeviceClient 设置到 CameraDeviceImpl 中进行管理。

//APP层调用openCamera方法
public void openCamera(@NonNull String cameraId,
        @NonNull final CameraDevice.StateCallback callback, @Nullable Handler handler)
        throws CameraAccessException {
        
    openCameraForUid(cameraId, callback, handler, USE_CALLING_UID);
}

//openCameraDeviceUserAsync方法
private CameraDevice openCameraDeviceUserAsync(String cameraId,
        CameraDevice.StateCallback callback, Handler handler, final int uid)
        throws CameraAccessException {
    CameraCharacteristics characteristics = getCameraCharacteristics(cameraId);
    CameraDevice device = null;

    synchronized (mLock) {

        ICameraDeviceUser cameraUser = null;

        android.hardware.camera2.impl.CameraDeviceImpl deviceImpl =   //实例化一个 CameraDeviceImpl。构造时传入了 CameraDevice.StateCallback 以及 Handler。
                new android.hardware.camera2.impl.CameraDeviceImpl(  
                    cameraId,
                    callback,
                    handler,
                    characteristics,
                    mContext.getApplicationInfo().targetSdkVersion);

        ICameraDeviceCallbacks callbacks = deviceImpl.getCallbacks(); //获取 CameraDeviceCallback 实例，这是提供给远端连接到 CameraDeviceImpl 的接口。

       try {
            if (supportsCamera2ApiLocked(cameraId)) {  //HAL3 中走的是这一部分逻辑，主要是从 CameraManagerGlobal 中获取 CameraService 的本地接口，通过它远端调用（采用 Binder 机制） connectDevice 方法连接到相机设备。
 　//注意返回的 cameraUser 实际上指向的是远端 CameraDeviceClient 的本地接口。
                // Use cameraservice's cameradeviceclient implementation for HAL3.2+ devices
                ICameraService cameraService = CameraManagerGlobal.get().getCameraService();
                if (cameraService == null) {
                    throw new ServiceSpecificException(
                        ICameraService.ERROR_DISCONNECTED,
                        "Camera service is currently unavailable");
                }
                cameraUser = cameraService.connectDevice(callbacks, cameraId,
                        mContext.getOpPackageName(), uid);
            } else {
                // Use legacy camera implementation for HAL1 devices
                int id;
                try {
                    id = Integer.parseInt(cameraId);
                } catch (NumberFormatException e) {
                    throw new IllegalArgumentException("Expected cameraId to be numeric, but it was: "
                            + cameraId);
                }

                Log.i(TAG, "Using legacy camera HAL.");
                cameraUser = CameraDeviceUserShim.connectBinderShim(callbacks, id);
            }
        } catch (ServiceSpecificException e) {
            /* Do something in */
            ......
            /* Do something out */
        }

        // TODO: factor out callback to be non-nested, then move setter to constructor
        // For now, calling setRemoteDevice will fire initial
        // onOpened/onUnconfigured callbacks.
        // This function call may post onDisconnected and throw CAMERA_DISCONNECTED if
        // cameraUser dies during setup.
        deviceImpl.setRemoteDevice(cameraUser); //将 CameraDeviceClient 设置到 CameraDeviceImpl 中进行管理。
        device = deviceImpl;
    }

    return device;
}

（2）CameraDeviceImpl

/frameworks/base/core/java/android/hardware/camera2/Impl/CameraDeviceImpl.java

在继续向下分析打开相机流程之前，先简单看看调用到的 CameraDeviceImpl 中的setRemoteDevice 方法，主要是将获取到的远端设备保存起来：

public void setRemoteDevice(ICameraDeviceUser remoteDevice) throws CameraAccessException {
    synchronized(mInterfaceLock) {
        // TODO: Move from decorator to direct binder-mediated exceptions
        // If setRemoteFailure already called, do nothing
        if (mInError) return;

        mRemoteDevice = new ICameraDeviceUserWrapper(remoteDevice); //通过 ICameraDeviceUserWrapper 给远端设备实例加上一层封装。

        IBinder remoteDeviceBinder = remoteDevice.asBinder(); //使用 Binder 机制的一些基本设置。
        // For legacy camera device, remoteDevice is in the same process, and
        // asBinder returns NULL.
        if (remoteDeviceBinder != null) {
            try {
                remoteDeviceBinder.linkToDeath(this, /*flag*/ 0); //如果这个binder消失，为标志信息注册一个接收器。
            } catch (RemoteException e) {
                CameraDeviceImpl.this.mDeviceHandler.post(mCallOnDisconnected);

                throw new CameraAccessException(CameraAccessException.CAMERA_DISCONNECTED,
                        "The camera device has encountered a serious error");
            }
        }

        mDeviceHandler.post(mCallOnOpened); //需此处触发 onOpened 与 onUnconfigured 这两个回调，每个回调都是通过 mDeviceHandler 启用一个新线程来调用的。
        mDeviceHandler.post(mCallOnUnconfigured);
    }
}

（3）CameraService

/frameworks/av/services/camera/libcameraservice/CameraService.cpp

通过 Binder 机制，我们远端调用了 connectDevice 方法，这个方法实现在 CameraService 类中。

Status CameraService::connectDevice(
        const sp<hardware::camera2::ICameraDeviceCallbacks>& cameraCb,
        const String16& cameraId,
        const String16& clientPackageName,
        int clientUid,
        /*out*/
        sp<hardware::camera2::ICameraDeviceUser>* device) {

    ATRACE_CALL();
    Status ret = Status::ok();
    String8 id = String8(cameraId);
    sp<CameraDeviceClient> client = nullptr;

　　 //此处调用的 connectHelper 方法才真正实现了连接逻辑（HAL1 时最终也调用到这个方法）。需要注意的是，设定的模板类型是 ICameraDeviceCallbacks 以及 CameraDeviceClient。
    ret = connectHelper<hardware::camera2::ICameraDeviceCallbacks,CameraDeviceClient>(cameraCb, id,
            CAMERA_HAL_API_VERSION_UNSPECIFIED, clientPackageName,
            clientUid, USE_CALLING_PID, API_2,
            /*legacyMode*/ false, /*shimUpdateOnly*/ false,
            /*out*/client);

    if(!ret.isOk()) {
        logRejected(id, getCallingPid(), String8(clientPackageName),
                ret.toString8());
        return ret;
    }

    *device = client; //client 指向的类型是 CameraDeviceClient，其实例则是最终的返回结果。
    return ret;
}

（4）ConnectHelper

template<class CALLBACK, class CLIENT>
Status CameraService::connectHelper(const sp<CALLBACK>& cameraCb, const String8& cameraId,
        int halVersion, const String16& clientPackageName, int clientUid, int clientPid,
        apiLevel effectiveApiLevel, bool legacyMode, bool shimUpdateOnly,
        /*out*/sp<CLIENT>& device) {
    binder::Status ret = binder::Status::ok();

    String8 clientName8(clientPackageName);

    /* Do something in */
    ......
    /* Do something out */

        sp<BasicClient> tmp = nullptr;
        //调用 makeClient 生成 CameraDeviceClient 实例。
        if(!(ret = makeClient(this, cameraCb, clientPackageName, cameraId, facing, clientPid,
                clientUid, getpid(), legacyMode, halVersion, deviceVersion, effectiveApiLevel,
                /*out*/&tmp)).isOk()) {
            return ret;
        }
        //初始化 CLIENT 实例。注意此处的模板类型 CLIENT 即是 CameraDeviceClient，传入的参数 mCameraProviderManager 则是与 HAL service 有关。 
        client = static_cast<CLIENT*>(tmp.get());

        LOG_ALWAYS_FATAL_IF(client.get() == nullptr, "%s: CameraService in invalid state",
                __FUNCTION__);

        err = client->initialize(mCameraProviderManager);

    /* Do something in */
    ......
    /* Do something out */

    // Important: release the mutex here so the client can call back into the service from its
    // destructor (can be at the end of the call)
    device = client;
    return ret;
} 

（5）makeClient

主要是根据 API 版本以及 HAL 版本来选择生成具体的 Client 实例，Client 就沿着前面分析下来的路径返回到 CameraDeviceImpl 实例中，被保存到 mRemoteDevice。

Status CameraService::makeClient(const sp<CameraService>& cameraService,
        const sp<IInterface>& cameraCb, const String16& packageName, const String8& cameraId,
        int facing, int clientPid, uid_t clientUid, int servicePid, bool legacyMode,
        int halVersion, int deviceVersion, apiLevel effectiveApiLevel,
        /*out*/sp<BasicClient>* client) {

    if (halVersion < 0 || halVersion == deviceVersion) {
        // Default path: HAL version is unspecified by caller, create CameraClient
        // based on device version reported by the HAL.
        switch(deviceVersion) {
          case CAMERA_DEVICE_API_VERSION_1_0:
            /* Do something in */
            ......
            /* Do something out */
          case CAMERA_DEVICE_API_VERSION_3_0:
          case CAMERA_DEVICE_API_VERSION_3_1:
          case CAMERA_DEVICE_API_VERSION_3_2:
          case CAMERA_DEVICE_API_VERSION_3_3:
          case CAMERA_DEVICE_API_VERSION_3_4:
            if (effectiveApiLevel == API_1) { // Camera1 API route
                sp<ICameraClient> tmp = static_cast<ICameraClient*>(cameraCb.get());
                *client = new Camera2Client(cameraService, tmp, packageName, cameraIdToInt(cameraId),
                        facing, clientPid, clientUid, servicePid, legacyMode);
            } else { // Camera2 API route : 实例化了 CameraDeviceClient 类作为 Client（注意此处构造传入了 ICameraDeviceCallbacks，这是连接到 CameraDeviceImpl 的远端回调）
                sp<hardware::camera2::ICameraDeviceCallbacks> tmp =
                        static_cast<hardware::camera2::ICameraDeviceCallbacks*>(cameraCb.get());
                *client = new CameraDeviceClient(cameraService, tmp, packageName, cameraId,
                        facing, clientPid, clientUid, servicePid);
            }
            break;
          default:
            // Should not be reachable
            ALOGE("Unknown camera device HAL version: %d", deviceVersion);
            return STATUS_ERROR_FMT(ERROR_INVALID_OPERATION,
                    "Camera device \"%s\" has unknown HAL version %d",
                    cameraId.string(), deviceVersion);
        }
    } else {
        /* Do something in */
        ......
        /* Do something out */
    }
    return Status::ok();
}

（6）client->initialize

传入CameraProviderManager获取到的device参数

status_t CameraDeviceClient::initialize(sp<CameraProviderManager> manager,
        const String8& monitorTags) {
    return initializeImpl(manager, monitorTags);
}

走到了Camera3Device::initialize方法 中

status_t Camera3Device::initialize(sp<CameraProviderManager> manager, const String8& monitorTags) {
    ATRACE_CALL();
.......

    sp<ICameraDeviceSession> session;
    ATRACE_BEGIN("CameraHal::openSession");
    status_t res = manager->openSession(mId.string(), this,
            /*out*/ &session);
    ATRACE_END();
.......

    res = manager->getCameraCharacteristics(mId.string(), &mDeviceInfo);

}