api 调用
- 获取CameraManager对象
CameraManager mCameraManager = (CameraManager) context.getSystemService(Context.CAMERA_SERVICE);
- openCamera
mCameraManager.openCamera(cameraId, callback, handler);
调用的是 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，来看一下它的对象实例化过程，它的实例化时在 CameraManager 的内部类 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) 也是通过 aidl 获取 CameraService 在 Native 中注册的 binder 对象，然后我们通过这个 binder 对象实例化 ICameraService 对象，我们看一下 ICameraService.aidl 通过编译生成的 ICameraService.java 中 asInterface 方法的实现(文件路径： /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);
}
首先会通过queryLocalInterface根据标识DESCRIPTOR在本地搜索接口，搜索到的是 ICameraService 内部类 Stub 构造函数内调用 attachInterface 与 binder 绑定的接口
public Stub() {
this.attachInterface(this, DESCRIPTOR);
}
如果没有实例化 Stub 对象的话则会返回代理类的对象（ICameraService 就没有 Stub 对象），代理类也是 Aidl 自动生成的；所以调用的 connectDevice 方法其实是 Proxy 类的
@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;
}
调用 transact 方法发起 RPC (远程过程调用)请求，同时当前线程挂起，然后服务端的 onTransact 方法会被调用，直到 RPC 过程返回，当前线程继续执行，从 _reply 中取出 RPC 过程中返回的结果
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;
}
... ...
}
}
对应 ICameraService.java， aidl 同时也在 Native 生成了 ICameraService.cpp，内有 BpCameraService （Native Proxy），及 BnCameraService 的实现；最终是在 BnCameraService 的 onTransact 方法内调用其子类 CameraService 的 connectDevice 方法实现 openCamera 的操作的
Status CameraService::connectDevice(
const sp& cameraCb,
const String16& cameraId,
const String16& clientPackageName,
int clientUid,
/*out*/
sp* device) {
ATRACE_CALL();
Status ret = Status::ok();
String8 id = String8(cameraId);
sp client = nullptr;
ret = connectHelper(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;
}