Android Camera getCameraIdList流程 (androidP)

Posted 2021-12-13 we1less

getCameraIdList() 按标识符返回当前连接的摄像头设备列表，包括其他 camera API 客户端可能正在使用的摄像头。

getCameraIdList

路径  frameworks/base/core/java/android/hardware/camera2/CameraManager.java

        获取idlist，在下面代码可以看出调用的是CameraManagerGlobal的getCameraIdList

@NonNull
public String[] getCameraIdList() throws CameraAccessException {
    return CameraManagerGlobal.get().getCameraIdList();
}

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CameraManagerGlobal::getCameraIdList

路径  frameworks/base/core/java/android/hardware/camera2/CameraManager.java

        这里面主要是获取到cameraService根据mDeviceStatus里面的值进行返回

        private final ArrayMap<String, Integer> mDeviceStatus = new ArrayMap<String, Integer>();

public String[] getCameraIdList() {
    String[] cameraIds = null;
    synchronized(mLock) {
        // Try to make sure we have an up-to-date list of camera devices.
        //获取cameraService
        connectCameraServiceLocked();

        int idCount = 0;
        for (int i = 0; i < mDeviceStatus.size(); i++) {
            int status = mDeviceStatus.valueAt(i);
            if (status == ICameraServiceListener.STATUS_NOT_PRESENT ||
                    status == ICameraServiceListener.STATUS_ENUMERATING) continue;
            idCount++;
        }
        cameraIds = new String[idCount];
        idCount = 0;
        for (int i = 0; i < mDeviceStatus.size(); i++) {
            int status = mDeviceStatus.valueAt(i);
            if (status == ICameraServiceListener.STATUS_NOT_PRESENT ||
                    status == ICameraServiceListener.STATUS_ENUMERATING) continue;
            cameraIds[idCount] = mDeviceStatus.keyAt(i);
            idCount++;
        }
    }
    //...接下来是排序
    return cameraIds;
}

mDeviceStatus的添加  onStatusChangedLocked

路径  frameworks/base/core/java/android/hardware/camera2/CameraManager.java

        可以明显看出这个数据结构中的值是受这个回调函数控制的，那么这个回调是何时调用的呢

private final ArrayMap<String, Integer> mDeviceStatus = new ArrayMap<String, Integer>();


private void onStatusChangedLocked(int status, String id) {
    //...
    Integer oldStatus;
    if (status == ICameraServiceListener.STATUS_NOT_PRESENT) {
        oldStatus = mDeviceStatus.remove(id);
    } else {
        oldStatus = mDeviceStatus.put(id, status);
    }
    //...


    final int callbackCount = mCallbackMap.size();
    for (int i = 0; i < callbackCount; i++) {
        Executor executor = mCallbackMap.valueAt(i);
        final AvailabilityCallback callback = mCallbackMap.keyAt(i);

        postSingleUpdate(callback, executor, id, status);
    }
} // onStatusChangedLocked

connectCameraServiceLocked 

路径  frameworks/base/core/java/android/hardware/camera2/CameraManager.java

        这个函数是上文中调用过的主要的用途就是获取链接到cameraService，并将自己作为监听注册给cameraService，在调用注册函数后会获取到cameraStatuses的一个数组，这个里面存放了关于摄像头设备的全部信息，遍历这个数组把他们放进mDeviceStatus中。当然这个类里面同样重写了onStatusChanged函数并且这里面同样调用了onStatusChangedLocked，这样当cameraService想要通知当前的摄像设备的状态时可以通过这个回调获取了

private void connectCameraServiceLocked() {
    //...
    IBinder cameraServiceBinder = ServiceManager.getService(CAMERA_SERVICE_BINDER_NAME);
    //...
    ICameraService cameraService = ICameraService.Stub.asInterface(cameraServiceBinder);

    try {
        CameraMetadataNative.setupGlobalVendorTagDescriptor();
    } catch (ServiceSpecificException e) {
        handleRecoverableSetupErrors(e);
    }

    try {
        CameraStatus[] cameraStatuses = cameraService.addListener(this);
        for (CameraStatus c : cameraStatuses) {
            onStatusChangedLocked(c.status, c.cameraId);
        }
        mCameraService = cameraService;
    } catch(ServiceSpecificException e) {
        // Unexpected failure
        throw new IllegalStateException("Failed to register a camera service listener", e);
    } catch (RemoteException e) {
        // Camera service is now down, leave mCameraService as null
    }
}
//####################################################################

@Override
public void onStatusChanged(int status, String cameraId) throws RemoteException {
    synchronized(mLock) {
        onStatusChangedLocked(status, cameraId);
    }
}

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