相机镜头和功能

注意：此页面参考了 Camera2 软件包。除非您的应用需要 Camera2 中的特定低级功能，否则我们建议您使用 CameraX。CameraX 和 Camera2 均支持 Android 5.0（API 级别 21）及更高版本。

许多现代 Android 设备在前置、后置或设备的两侧都配备了两个或更多摄像头。每个镜头都可能具有独特的功能，例如连拍、手动控制或运动跟踪。支票存款应用程序可能只使用第一个后置摄像头，而社交媒体应用程序可能默认使用前置摄像头，但允许用户在所有可用镜头之间切换。它还可以记住用户的选择。

此页面介绍如何列出摄像头镜头及其功能，以便您可以在应用程序中根据具体情况决定使用哪个镜头。以下代码片段检索所有摄像头的列表并对其进行迭代

Kotlin

try {
    val cameraIdList = cameraManager.cameraIdList // may be empty

    // iterate over available camera devices
    for (cameraId in cameraIdList) {
        val characteristics = cameraManager.getCameraCharacteristics(cameraId)
        val cameraLensFacing = characteristics.get(CameraCharacteristics.LENS_FACING)
        val cameraCapabilities = characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES)

        // check if the selected camera device supports basic features
        // ensures backward compatibility with the original Camera API
        val isBackwardCompatible = cameraCapabilities?.contains(
            CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE) ?: false
        ...
    }
} catch (e: CameraAccessException) {
    e.message?.let { Log.e(TAG, it) }
    ...
}

Java

try {
    String[] cameraIdList = cameraManager.getCameraIdList(); // may be empty

    // iterate over available camera devices
    for (String cameraId : cameraIdList) {
        CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(cameraId);
        int cameraLensFacing = characteristics.get(CameraCharacteristics.LENS_FACING);
        int[] cameraCapabilities =
            characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES);

        // check if the selected camera device supports basic features
        // ensures backward compatibility with the original Camera API
        boolean isBackwardCompatible = false;
        for (int capability : cameraCapabilities) {
            if (capability == CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE) {
                isBackwardCompatible = true;
                break;
            }
        }
        ...
    }
} catch (CameraAccessException e) {
    Log.e(TAG, e.getMessage());
    ...
}

变量 cameraLensFacing 描述了摄像头相对于设备屏幕的方向，并具有以下值之一

有关镜头朝向配置的更多信息，请参阅 CameraCharacteristics.LENS_FACING。

前面代码示例中的变量 cameraCapabilities 包含有关各种功能的信息，包括摄像头是否能够生成标准帧作为输出（与仅生成深度传感器数据等相反）。您可以查看 CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE 是否是摄像头列出的功能之一，该功能作为标志存储在 isBackwardCompatible 中。

选择合理的默认值

在您的应用中，您可能希望默认打开特定摄像头（如果可用）。例如，自拍应用可能会打开前置摄像头，而增强现实应用可能会以后置摄像头启动。以下函数返回第一个朝向给定方向的摄像头

Kotlin

fun getFirstCameraIdFacing(cameraManager: CameraManager,
                           facing: Int = CameraMetadata.LENS_FACING_BACK): String? {
    try {
        // Get list of all compatible cameras
        val cameraIds = cameraManager.cameraIdList.filter {
            val characteristics = cameraManager.getCameraCharacteristics(it)
            val capabilities = characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES)
            capabilities?.contains(
                    CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE) ?: false
        }

        // Iterate over the list of cameras and return the first one matching desired
        // lens-facing configuration
        cameraIds.forEach {
            val characteristics = cameraManager.getCameraCharacteristics(it)
            if (characteristics.get(CameraCharacteristics.LENS_FACING) == facing) {
                return it
            }
        }

        // If no camera matched desired orientation, return the first one from the list
        return cameraIds.firstOrNull()
    } catch (e: CameraAccessException) {
        e.message?.let { Log.e(TAG, it) }
    }
}

Java

public String getFirstCameraIdFacing(CameraManager cameraManager, @Nullable Integer facing) {
    if (facing == null) facing = CameraMetadata.LENS_FACING_BACK;
    String cameraId = null;

    try {
        // Get a list of all compatible cameras
        String[] cameraIdList = cameraManager.getCameraIdList();

        // Iterate over the list of cameras and return the first one matching desired
        // lens-facing configuration and backward compatibility
        for (String id : cameraIdList) {
            CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(id);
            int[] capabilities = characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES);
            for (int capability : capabilities) {
                if (capability == CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE
                        && characteristics.get(CameraCharacteristics.LENS_FACING).equals(facing)) {
                    cameraId = id;
                    break;
                }
            }
        }

        // If no camera matches the desired orientation, return the first one from the list
        cameraId = cameraIdList[0];
    } catch (CameraAccessException e) {
        Log.e(TAG, "getFirstCameraIdFacing: " + e.getMessage());
    }

    return cameraId;
}

启用摄像头切换

许多摄像头应用都允许用户在摄像头之间切换

图 1. Google 相机应用中的切换摄像头按钮

许多设备有多个朝向相同方向的摄像头。有些甚至有外部 USB 摄像头。要为用户提供一个允许他们在不同朝向的摄像头之间切换的 UI，请为每个可能的镜头朝向配置选择第一个可用的摄像头。

虽然没有通用的选择下一个摄像头的逻辑，但以下代码适用于大多数用例

Kotlin

fun filterCompatibleCameras(cameraIds: Array<String>,
                            cameraManager: CameraManager): List<String> {
    return cameraIds.filter {
        val characteristics = cameraManager.getCameraCharacteristics(it)
        characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES)?.contains(
                CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE) ?: false
    }
}

fun filterCameraIdsFacing(cameraIds: List<String>, cameraManager: CameraManager,
                          facing: Int): List<String> {
    return cameraIds.filter {
        val characteristics = cameraManager.getCameraCharacteristics(it)
        characteristics.get(CameraCharacteristics.LENS_FACING) == facing
    }
}

fun getNextCameraId(cameraManager: CameraManager, currCameraId: String? = null): String? {
    // Get all front, back and external cameras in 3 separate lists
    val cameraIds = filterCompatibleCameras(cameraManager.cameraIdList, cameraManager)
    val backCameras = filterCameraIdsFacing(
            cameraIds, cameraManager, CameraMetadata.LENS_FACING_BACK)
    val frontCameras = filterCameraIdsFacing(
            cameraIds, cameraManager, CameraMetadata.LENS_FACING_FRONT)
    val externalCameras = filterCameraIdsFacing(
            cameraIds, cameraManager, CameraMetadata.LENS_FACING_EXTERNAL)

    // The recommended order of iteration is: all external, first back, first front
    val allCameras = (externalCameras + listOf(
            backCameras.firstOrNull(), frontCameras.firstOrNull())).filterNotNull()

    // Get the index of the currently selected camera in the list
    val cameraIndex = allCameras.indexOf(currCameraId)

    // The selected camera may not be in the list, for example it could be an
    // external camera that has been removed by the user
    return if (cameraIndex == -1) {
        // Return the first camera from the list
        allCameras.getOrNull(0)
    } else {
        // Return the next camera from the list, wrap around if necessary
        allCameras.getOrNull((cameraIndex + 1) % allCameras.size)
    }
}

Java

public List<String> filterCompatibleCameras(CameraManager cameraManager, String[] cameraIds) {
    final List<String> compatibleCameras = new ArrayList<>();

    try {
        for (String id : cameraIds) {
            CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(id);
            int[] capabilities = characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES);
            for (int capability : capabilities) {
                if (capability == CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE) {
                    compatibleCameras.add(id);
                }
            }
        }
    } catch (CameraAccessException e) {
        Log.e(TAG, "filterCompatibleCameras: " + e.getMessage());
    }

    return compatibleCameras;
}

public List<String> filterCameraIdsFacing(CameraManager cameraManager, List<String> cameraIds, int lensFacing) {
    final List<String> compatibleCameras = new ArrayList<>();

    try {
        for (String id : cameraIds) {
            CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(id);
            if (characteristics.get(CameraCharacteristics.LENS_FACING) == lensFacing) {
                compatibleCameras.add(id);
            }
        }
    } catch (CameraAccessException e) {
        Log.e(TAG, "filterCameraIdsFacing: " + e.getMessage());
    }

    return compatibleCameras;
}

public String getNextCameraId(CameraManager cameraManager, @Nullable String currentCameraId) {
    String nextCameraId = null;

    try {
        // Get all front, back, and external cameras in 3 separate lists
        List<String> compatibleCameraIds = filterCompatibleCameras(cameraManager, cameraManager.getCameraIdList());
        List<String> backCameras = filterCameraIdsFacing(cameraManager, compatibleCameraIds, CameraMetadata.LENS_FACING_BACK);
        List<String> frontCameras = filterCameraIdsFacing(cameraManager, compatibleCameraIds, CameraMetadata.LENS_FACING_FRONT);
        List<String>externalCameras = filterCameraIdsFacing(cameraManager, compatibleCameraIds, CameraMetadata.LENS_FACING_EXTERNAL);

        // The recommended order of iteration is: all external, first back, first front
        List<String> allCameras = new ArrayList<>(externalCameras);
        if (!backCameras.isEmpty()) allCameras.add(backCameras.get(0));
        if (!frontCameras.isEmpty()) allCameras.add(frontCameras.get(0));

        // Get the index of the currently selected camera in the list
        int cameraIndex = allCameras.indexOf(currentCameraId);

        // The selected camera may not be in the list, for example it could be an
        // external camera that has been removed by the user
        if (cameraIndex == -1) {
            // Return the first camera from the list
            nextCameraId = !allCameras.isEmpty() ? allCameras.get(0) : null;
        else {
            if (!allCameras.isEmpty()) {
                // Return the next camera from the list, wrap around if necessary
                nextCameraId = allCameras.get((cameraIndex + 1) % allCameras.size());
            }
        }
    } catch (CameraAccessException e) {
        Log.e(TAG, "getNextCameraId: " + e.getMessage());
    }

    return nextCameraId;
}

此代码适用于具有许多不同配置的大量设备。有关处理极端情况的更多信息，请参阅 CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_LOGICAL_MULTI_CAMERA。

创建兼容的应用

对于仍在使用已弃用的 Camera API 的应用，Camera.getNumberOfCameras() 返回的摄像头数量取决于 OEM 实现。如果系统中存在逻辑多摄像头，为了保持应用向后兼容性，此方法将仅为每个逻辑摄像头和底层物理摄像头组公开一个摄像头。使用 Camera2 API 查看所有摄像头。

有关摄像头方向的更多背景信息，请参阅 Camera.CameraInfo.orientation。

通常，使用 Camera.getCameraInfo() API 查询所有摄像头的 orientation，并仅为在摄像头之间切换的用户公开每个可用方向的一个摄像头。

适应所有设备类型

不要假设您的应用始终在具有一个或两个摄像头的便携式设备上运行。相反，为应用选择最合适的摄像头。如果您不需要特定摄像头，请选择第一个朝向所需方向的摄像头。如果连接了外部摄像头，您可能会假设用户更喜欢将其作为默认摄像头。