注意:本页介绍的是 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 都支持 Android 5.0(API 级别 21)及更高版本。
许多现代 Android 设备的前置、后置或后置摄像头都有两个或更多个摄像头 两个设备之间。每个镜头都可以有独特的功能,例如连拍、 手动控制或动作跟踪。用于存入支票的应用可能只能使用 第一个后置摄像头,而社交媒体应用可能会默认为 但要为用户提供一个选项,让他们可以在所有可用设备间 它还能记住用户的选择。
本页将介绍如何列出相机镜头及其功能, 可以在您的应用中决定在特定情况下应使用哪种镜头。 以下代码段会检索所有相机的列表,并迭代 :
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
描述了镜头面向的方向
相对于设备屏幕,并具有以下值之一:
CameraMetadata.LENS_FACING_FRONT
CameraMetadata.LENS_FACING_BACK
CameraMetadata.LENS_FACING_EXTERNAL
如需详细了解面向镜头的配置,请参阅
CameraCharacteristics.LENS_FACING
。
上述代码示例中的变量 cameraCapabilities
包含
其他功能的相关信息,包括摄像头是否处于
能够生成标准帧作为输出(比方说,
深度传感器数据)。您可以查看
CameraMetadata.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE
是相机列出的功能之一,在
isBackwardCompatible
。
选择合理的默认设置
在您的应用中,您可能需要默认打开特定相机 (如果有)。例如,自拍应用可能会打开设备的 而增强现实应用则可能从后置摄像头开始。 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切换摄像头的选项:
![](https://developer.android.google.cn/static/images/training/camera/camera2/camera-enumeration-1.png?authuser=9&hl=ro)
许多设备都有多个朝向同一方向的摄像头。有些人甚至还有 外接 USB 摄像头。为用户提供一个界面 请为各个摄像头选择第一个可用的摄像头 。
尽管没有用于选择下一个摄像头的通用逻辑, 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类型设备的大型
配置。如需详细了解如何考虑边缘情况,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,摄像头的数量
那个
Camera.getNumberOfCameras()
退货金额取决于 OEM 的实现情况。如果
为保持应用的向后兼容性,此方法仅公开
每个逻辑摄像头和底层物理摄像头组的摄像头。
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
。
一般来说,使用
Camera.getCameraInfo()
用于查询所有相机的 API
orientation
、
并针对每个可用的屏幕方向仅展示一个摄像头
来切换摄像头
适应所有设备类型
不要假设应用总是在具有一个或 两台摄像头而是应选择最适合该应用的摄像头。如果您 不需要特定摄像头,请选择第一个面向所需摄像头的 。如果连接了外接摄像头,您可能会认为用户 倾向于使用默认设置