相机镜头和功能

注意:本页介绍的是 Camera2 软件包。除非您的应用需要 Camera2 的特定低层级功能,否则我们建议您使用 CameraX。CameraX 和 Camera2 都支持 Android 5.0(API 级别 21)及更高版本。

许多现代 Android 设备的正面、背面或两侧都有两个或更多摄像头。每个镜头都可以具有独特的功能,例如连拍、手动控制或动作跟踪。用于存入支票的应用可能仅使用第一个后置摄像头,而社交媒体应用可能默认使用前置摄像头,但用户可以选择在所有可用镜头之间切换。系统还会记住用户的选择。

本页介绍了如何列出相机镜头及其功能,以便您在应用中决定在给定情况下使用哪种镜头。以下代码段会检索所有相机的列表,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 描述相机相对于设备屏幕朝向的方向,并具有以下值之一:

如需详细了解镜头朝向配置,请参阅 CameraCharacteristics.LENS_FACING

上述代码示例中的变量 cameraCapabilities 包含有关其他功能的信息,包括相机能否生成标准帧作为输出(例如,与只有深度传感器数据相反)。您可以查找 CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE 是否为相机列出的功能之一,该功能以标志的形式存储在 isBackwardCompatible 中。

选择合理的默认设置

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从后置摄像头启动。以下函数会返回面向指定方向的第一个镜头:

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;
}

允许切换摄像头

许多相机应用为用户提供了切换摄像头的选项:

图 1. Google 相机应用中的切换摄像头按钮

许多设备有多个朝同一方向的摄像头。有些甚至配有外接 USB 摄像头。如需为用户提供一个界面,使其能够在不同的朝向摄像头之间切换,请针对每种可能的镜头朝向配置选择第一个可用的摄像头。

虽然没有用于选择下一个摄像头的通用逻辑,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。如需详细了解如何考虑极端情况,请参阅 CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_LOGICAL_MULTI_CAMERA

打造兼容的应用

对于仍在使用已废弃的 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 查看所有相机。

如需详细了解有关摄像头方向的背景信息,请参阅 Camera.CameraInfo.orientation

一般情况下,请使用 Camera.getCameraInfo() API 查询所有摄像头 orientation,并针对每种可用方向仅将一个摄像头公开给在摄像头之间切换的用户。

适合所有设备类型

不要假设应用始终在配有一个或两个摄像头的手持设备上运行。而是选择最适合应用的摄像头。如果您不需要特定的摄像头,请选择第一个朝向所需方向的摄像头。如果连接了外接摄像头,您可能会认为用户首选它作为默认摄像头。