Android Camera原理之openCamera模塊(二)
在上一篇文章《Android Camera原理之openCamera模塊(一)》咱們主要介紹了openCamera的調用流程以及camera模塊涉及到的4個層次之間的調用關係，可是一些細節問題並無闡釋到，本文咱們補充一下細節問題，力求豐滿整個openCamera模塊的知識體系。
在《Android Camera模塊解析之拍照》一文中談到了調用openCamera方法：android
manager.openCamera(mCameraId, mStateCallback, mBackgroundHandler);
這個manager就是CameraManager實例，openCamera方法上一篇文章已經介紹地比較清楚了，可是第二個參數mStateCallback沒有深刻講解，你們只知道是一個相機狀態的回調，可是這個狀態很重要。這個狀態回調會告知開發者當前的camera處於什麼狀態，在確切得到這個狀態以後，才能進行下一步的操做。例如我打開camera是成功仍是失敗了，若是不知道的話是不能進行下一步的操做的。安全
private final CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() {
@Override
public void onOpened(@NonNull CameraDevice cameraDevice) {
// This method is called when the camera is opened. We start camera preview here.
mCameraOpenCloseLock.release();
mCameraDevice = cameraDevice;
createCameraPreviewSession();
}
@Override
public void onDisconnected(@NonNull CameraDevice cameraDevice) {
mCameraOpenCloseLock.release();
cameraDevice.close();
mCameraDevice = null;
}
@Override
public void onError(@NonNull CameraDevice cameraDevice, int error) {
mCameraOpenCloseLock.release();
cameraDevice.close();
mCameraDevice = null;
Activity activity = getActivity();
if (null != activity) {
activity.finish();
}
}
};
本文想搞清楚的一點是：Camera狀態是如何回調的？
因爲上一篇openCamera的文章已經談到了詳細的調用流程，這裏不會贅述了。session
1.openCameraDeviceUserAsync中StateCallback
openCamera會調用到openCameraDeviceUserAsync(...)中，固然也會把它的StateCallback參數傳進來，這個參數和獲取到的CameraCharacteristics一塊兒傳入CameraDeviceImpl的構造函數中。app
android.hardware.camera2.impl.CameraDeviceImpl deviceImpl =
new android.hardware.camera2.impl.CameraDeviceImpl(
cameraId,
callback,
executor,
characteristics,
mContext.getApplicationInfo().targetSdkVersion);
可是傳入cameraService的回調參數卻不是這個回調，看一下代碼：ide
ICameraDeviceCallbacks callbacks = deviceImpl.getCallbacks();
//......
cameraUser = cameraService.connectDevice(callbacks, cameraId,
mContext.getOpPackageName(), uid);
這個callbacks是CameraDeviceImpl實例中的參數，那麼這個callbacks和咱們傳入的StateCallback有什麼關係了，仍是要去CameraDeviceImpl看一下。函數
public CameraDeviceImpl(String cameraId, StateCallback callback, Executor executor,
CameraCharacteristics characteristics, int appTargetSdkVersion) {
if (cameraId == null || callback == null || executor == null || characteristics == null) {
throw new IllegalArgumentException("Null argument given");
}
mCameraId = cameraId;
mDeviceCallback = callback;
mDeviceExecutor = executor;
mCharacteristics = characteristics;
mAppTargetSdkVersion = appTargetSdkVersion;
final int MAX_TAG_LEN = 23;
String tag = String.format("CameraDevice-JV-%s", mCameraId);
if (tag.length() > MAX_TAG_LEN) {
tag = tag.substring(0, MAX_TAG_LEN);
}
TAG = tag;
Integer partialCount =
mCharacteristics.get(CameraCharacteristics.REQUEST_PARTIAL_RESULT_COUNT);
if (partialCount == null) {
// 1 means partial result is not supported.
mTotalPartialCount = 1;
} else {
mTotalPartialCount = partialCount;
}
}
- 構造函數中傳入的StateCallback賦給了CameraDeviceImpl中的mDeviceCallback
private final CameraDeviceCallbacks mCallbacks = new CameraDeviceCallbacks();
public CameraDeviceCallbacks getCallbacks() {
return mCallbacks;
}
public class CameraDeviceCallbacks extends ICameraDeviceCallbacks.Stub {
//......
}
- CameraDeviceCallbacks繼承ICameraDeviceCallbacks.Stub，而ICameraDeviceCallbacks.Stub是能夠在Binder IPC中傳輸的對象，很顯然這個纔是應用程序與CameraService通訊的回調，在這個回調中的執行方法標識當前的camera的執行狀態
2.CameraDeviceCallbacks回調
ICameraDeviceCallbacks.aidl自動生成的android/hardware/camera2/ICameraDeviceCallbacks.h文件post
class ICameraDeviceCallbacksDefault : public ICameraDeviceCallbacks {
public:
::android::IBinder* onAsBinder() override;
::android::binder::Status onDeviceError(int32_t errorCode, const ::android::hardware::camera2::impl::CaptureResultExtras& resultExtras) override;
::android::binder::Status onDeviceIdle() override;
::android::binder::Status onCaptureStarted(const ::android::hardware::camera2::impl::CaptureResultExtras& resultExtras, int64_t timestamp) override;
::android::binder::Status onResultReceived(const ::android::hardware::camera2::impl::CameraMetadataNative& result, const ::android::hardware::camera2::impl::CaptureResultExtras& resultExtras, const ::std::vector<::android::hardware::camera2::impl::PhysicalCaptureResultInfo>& physicalCaptureResultInfos) override;
::android::binder::Status onPrepared(int32_t streamId) override;
::android::binder::Status onRepeatingRequestError(int64_t lastFrameNumber, int32_t repeatingRequestId) override;
::android::binder::Status onRequestQueueEmpty() override;
};
這個回調函數是從CameraService中調上來的。下面的回調包含了Camera執行過程當中的各類狀態，執行成功、執行失敗、數據接收成功等等。這兒暫時不展開描述，等後面capture image的時候會詳細闡釋。學習
- onDeviceError
- onDeviceIdle
- onCaptureStarted
- onResultReceived
- onPrepared
- onRepeatingRequestError
- onRequestQueueEmpty
3.StateCallback回調
StateCallback是openCamera傳入的3個參數中的一個，這是一個標識當前camera鏈接狀態的回調。ui
public static abstract class StateCallback {
public static final int ERROR_CAMERA_IN_USE = 1;
public static final int ERROR_MAX_CAMERAS_IN_USE = 2;
public static final int ERROR_CAMERA_DISABLED = 3;
public static final int ERROR_CAMERA_DEVICE = 4;
public static final int ERROR_CAMERA_SERVICE = 5;
/** @hide */
@Retention(RetentionPolicy.SOURCE)
@IntDef(prefix = {"ERROR_"}, value =
{ERROR_CAMERA_IN_USE,
ERROR_MAX_CAMERAS_IN_USE,
ERROR_CAMERA_DISABLED,
ERROR_CAMERA_DEVICE,
ERROR_CAMERA_SERVICE })
public @interface ErrorCode {};
public abstract void onOpened(@NonNull CameraDevice camera); // Must implement
public void onClosed(@NonNull CameraDevice camera) {
// Default empty implementation
}
public abstract void onDisconnected(@NonNull CameraDevice camera); // Must implement
public abstract void onError(@NonNull CameraDevice camera,
@ErrorCode int error); // Must implement
}
- onOpened回調：
當前camera device已經被打開了，會觸發這個回調。探明camera的狀態是opened了，這是能夠開始createCaptureSession開始使用camera 捕捉圖片或者視頻了。
觸發onOpened回調的地方在setRemoteDevice(...)，這個函數在connectDevice(...)鏈接成功以後執行，代表當前的camera device已經鏈接成功了，觸發camera 可以打開的回調。this
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);
IBinder remoteDeviceBinder = remoteDevice.asBinder();
// For legacy camera device, remoteDevice is in the same process, and
// asBinder returns NULL.
if (remoteDeviceBinder != null) {
try {
remoteDeviceBinder.linkToDeath(this, /*flag*/ 0);
} catch (RemoteException e) {
CameraDeviceImpl.this.mDeviceExecutor.execute(mCallOnDisconnected);
throw new CameraAccessException(CameraAccessException.CAMERA_DISCONNECTED,
"The camera device has encountered a serious error");
}
}
mDeviceExecutor.execute(mCallOnOpened);
mDeviceExecutor.execute(mCallOnUnconfigured);
}
}
private final Runnable mCallOnOpened = new Runnable() {
@Override
public void run() {
StateCallbackKK sessionCallback = null;
synchronized(mInterfaceLock) {
if (mRemoteDevice == null) return; // Camera already closed
sessionCallback = mSessionStateCallback;
}
if (sessionCallback != null) {
sessionCallback.onOpened(CameraDeviceImpl.this);
}
mDeviceCallback.onOpened(CameraDeviceImpl.this);
}
};
- onClosed回調：
camera device已經被關閉，這個回調被觸發。通常是終端開發者closeCamera的時候會釋放當前持有的camera device，這是正常的現象。
public void close() {
synchronized (mInterfaceLock) {
if (mClosing.getAndSet(true)) {
return;
}
if (mRemoteDevice != null) {
mRemoteDevice.disconnect();
mRemoteDevice.unlinkToDeath(this, /*flags*/0);
}
if (mRemoteDevice != null || mInError) {
mDeviceExecutor.execute(mCallOnClosed);
}
mRemoteDevice = null;
}
}
private final Runnable mCallOnClosed = new Runnable() {
private boolean mClosedOnce = false;
@Override
public void run() {
if (mClosedOnce) {
throw new AssertionError("Don't post #onClosed more than once");
}
StateCallbackKK sessionCallback = null;
synchronized(mInterfaceLock) {
sessionCallback = mSessionStateCallback;
}
if (sessionCallback != null) {
sessionCallback.onClosed(CameraDeviceImpl.this);
}
mDeviceCallback.onClosed(CameraDeviceImpl.this);
mClosedOnce = true;
}
};
- onDisconnected回調：
camera device再也不可用，打開camera device失敗了，通常是由於權限或者安全策略問題致使camera device打不開。一旦鏈接camera device出現ERROR_CAMERA_DISCONNECTED問題了，這是函數就會被回調，表示當前camera device處於斷開的狀態。- onError回調：
調用camera device的時候出現了嚴重的問題。執行CameraService-->connectDevice 出現異常了
} catch (ServiceSpecificException e) {
if (e.errorCode == ICameraService.ERROR_DEPRECATED_HAL) {
throw new AssertionError("Should've gone down the shim path");
} else if (e.errorCode == ICameraService.ERROR_CAMERA_IN_USE ||
e.errorCode == ICameraService.ERROR_MAX_CAMERAS_IN_USE ||
e.errorCode == ICameraService.ERROR_DISABLED ||
e.errorCode == ICameraService.ERROR_DISCONNECTED ||
e.errorCode == ICameraService.ERROR_INVALID_OPERATION) {
// Received one of the known connection errors
// The remote camera device cannot be connected to, so
// set the local camera to the startup error state
deviceImpl.setRemoteFailure(e);
if (e.errorCode == ICameraService.ERROR_DISABLED ||
e.errorCode == ICameraService.ERROR_DISCONNECTED ||
e.errorCode == ICameraService.ERROR_CAMERA_IN_USE) {
// Per API docs, these failures call onError and throw
throwAsPublicException(e);
}
} else {
// Unexpected failure - rethrow
throwAsPublicException(e);
}
} catch (RemoteException e) {
// Camera service died - act as if it's a CAMERA_DISCONNECTED case
ServiceSpecificException sse = new ServiceSpecificException(
ICameraService.ERROR_DISCONNECTED,
"Camera service is currently unavailable");
deviceImpl.setRemoteFailure(sse);
throwAsPublicException(sse);
}
deviceImpl.setRemoteFailure(e);是執行onError回調的函數。
小結
Camera的知識點很是多，咱們從openCamera講起，也是但願從代碼實踐中真正瞭解camera的調用流程，由淺入深的學習camera知識。下面咱們會繼續講解鏈接成功以後，也就是StateCallback-->onOpened回調中camera會如何操做。敬請期待，不足之處，敬請諒解。
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