api 調(diào)用

• 獲取CameraManager對象

CameraManager mCameraManager = (CameraManager) context.getSystemService(Context.CAMERA_SERVICE);

• openCamera

mCameraManager.openCamera(cameraId, callback, handler);

調(diào)用的是 CameraManager 中的 openCameraDeviceUserAsync 方法

    private CameraDevice openCameraDeviceUserAsync(String cameraId,
            CameraDevice.StateCallback callback, Executor executor, final int uid)
            throws CameraAccessException {
... ...
                    // 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);
... ...

        return device;
    }

ICameraService 是 aidl，來看一下它的對象實(shí)例化過程，它的實(shí)例化時(shí)在 CameraManager 的內(nèi)部類 CameraManagerGlobal 的 connectCameraServiceLocked 方法中

        private void connectCameraServiceLocked() {
            // Only reconnect if necessary
            if (mCameraService != null || sCameraServiceDisabled) return;

            Log.i(TAG, "Connecting to camera service");

            IBinder cameraServiceBinder = ServiceManager.getService(CAMERA_SERVICE_BINDER_NAME);
            if (cameraServiceBinder == null) {
                // Camera service is now down, leave mCameraService as null
                return;
            }
            try {
                cameraServiceBinder.linkToDeath(this, /*flags*/ 0);
            } catch (RemoteException e) {
                // Camera service is now down, leave mCameraService as null
                return;
            }

            ICameraService cameraService = ICameraService.Stub.asInterface(cameraServiceBinder);
... ...
        }

ServiceManager.getService(CAMERA_SERVICE_BINDER_NAME) 也是通過 aidl 獲取 CameraService 在 Native 中注冊的 binder 對象，然后我們通過這個 binder 對象實(shí)例化 ICameraService 對象，我們看一下 ICameraService.aidl 通過編譯生成的 ICameraService.java 中 asInterface 方法的實(shí)現(xiàn)(文件路徑： /android/out/soong/.intermediates/frameworks/base/framework/android_common/gen/aidl/frameworks/av/camera/aidl/android/hardware/ICameraService.java)

public static android.hardware.ICameraService asInterface(android.os.IBinder obj) {
    if ((obj == null)) {
        return null;
    }
    android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
    if (((iin != null) && (iin instanceof android.hardware.ICameraService))) {
        return ((android.hardware.ICameraService) iin);
    }
    return new android.hardware.ICameraService.Stub.Proxy(obj);
}

首先會通過queryLocalInterface根據(jù)標(biāo)識DESCRIPTOR在本地搜索接口，搜索到的是 ICameraService 內(nèi)部類 Stub 構(gòu)造函數(shù)內(nèi)調(diào)用 attachInterface 與 binder 綁定的接口

public Stub() {
    this.attachInterface(this, DESCRIPTOR);
}

如果沒有實(shí)例化 Stub 對象的話則會返回代理類的對象（ICameraService 就沒有 Stub 對象），代理類也是 Aidl 自動生成的；所以調(diào)用的 connectDevice 方法其實(shí)是 Proxy 類的

@Override
public android.hardware.camera2.ICameraDeviceUser connectDevice(android.hardware.camera2.ICameraDeviceCallbacks callbacks, java.lang.String cameraId, java.lang.String opPackageName, int clientUid) throws android.os.RemoteException {
    android.os.Parcel _data = android.os.Parcel.obtain();
    android.os.Parcel _reply = android.os.Parcel.obtain();
    android.hardware.camera2.ICameraDeviceUser _result;
    try {
        _data.writeInterfaceToken(DESCRIPTOR);
        _data.writeStrongBinder((((callbacks != null)) ? (callbacks.asBinder()) : (null)));
        _data.writeString(cameraId);
        _data.writeString(opPackageName);
        _data.writeInt(clientUid);
        mRemote.transact(Stub.TRANSACTION_connectDevice, _data, _reply, 0);
        _reply.readException();
        _result = android.hardware.camera2.ICameraDeviceUser.Stub.asInterface(_reply.readStrongBinder());
    } finally {
        _reply.recycle();
        _data.recycle();
    }
    return _result;
}

調(diào)用 transact 方法發(fā)起 RPC (遠(yuǎn)程過程調(diào)用)請求，同時(shí)當(dāng)前線程掛起，然后服務(wù)端的 onTransact 方法會被調(diào)用，直到 RPC 過程返回，當(dāng)前線程繼續(xù)執(zhí)行，從 _reply 中取出 RPC 過程中返回的結(jié)果

public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException {
            java.lang.String descriptor = DESCRIPTOR;
            switch (code) {
... ...
                case TRANSACTION_connectDevice: {
                    data.enforceInterface(descriptor);
                    android.hardware.camera2.ICameraDeviceCallbacks _arg0;
                    _arg0 = android.hardware.camera2.ICameraDeviceCallbacks.Stub.asInterface(data.readStrongBinder());
                    java.lang.String _arg1;
                    _arg1 = data.readString();
                    java.lang.String _arg2;
                    _arg2 = data.readString();
                    int _arg3;
                    _arg3 = data.readInt();
                    android.hardware.camera2.ICameraDeviceUser _result = this.connectDevice(_arg0, _arg1, _arg2, _arg3);
                    reply.writeNoException();
                    reply.writeStrongBinder((((_result != null)) ? (_result.asBinder()) : (null)));
                    return true;
                }
... ...
            }
        }

對應(yīng) ICameraService.java， aidl 同時(shí)也在 Native 生成了 ICameraService.cpp，內(nèi)有 BpCameraService （Native Proxy），及 BnCameraService 的實(shí)現(xiàn)；最終是在 BnCameraService 的 onTransact 方法內(nèi)調(diào)用其子類 CameraService 的 connectDevice 方法實(shí)現(xiàn) openCamera 的操作的

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;
    ret = connectHelper<hardware::camera2::ICameraDeviceCallbacks,CameraDeviceClient>(cameraCb, id,
            /*api1CameraId*/-1,
            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;
    return ret;
}