在Android设备中，做预览拍照的需求的时候，我们会指定

CameraSelector DEFAULT_FRONT_CAMERA前置
或者后置CameraSelector DEFAULT_BACK_CAMERA

如果你使用的是平板或者工业平板，那么就会遇到多摄像头以及外置摄像头问题，简单的指定前后置是不行的，哪怕是USB 外置也有挂载两个的情况 ，本文就是写于两个外置的特殊情况作为验证，所以我们必须能获取所有可用的摄像头，我们以最新的预览拍照控件为例（
单摄像头推荐PreviewView+CameraSelector 与挂载的位置相关 且绑定了activity lifecycle
多摄像头推荐Surfaceview+CameraId 与id相关 surfaceview方式获取id在下面

PreviewView

为例初始化的时候需要使用

CameraSelector去绑定拍照的UseCase

    @MainThread@NonNullpublic Camera bindToLifecycle(@NonNull LifecycleOwner lifecycleOwner,@NonNull CameraSelector cameraSelector,@NonNull UseCase... useCases) {if (getCameraOperatingMode() == CAMERA_OPERATING_MODE_CONCURRENT) {throw new UnsupportedOperationException("bindToLifecycle for single camera is not "+ "supported in concurrent camera mode, call unbindAll() first");}setCameraOperatingMode(CAMERA_OPERATING_MODE_SINGLE);Camera camera = bindToLifecycle(lifecycleOwner, cameraSelector, null, emptyList(),useCases);return camera;}

因为我们需要获取所有可用的摄像头类似旧版的CameraId

将下面代码放入activity获取

   val cameraProviderFuture = ProcessCameraProvider.getInstance(this)cameraProviderFuture.addListener({LogUtils.log("摄像头结果返回")val cameraProvider = cameraProviderFuture.get()var textC = ""val cameraInfos = cameraProvider.availableCameraInfosvar isSupportBack = falsevar isSupportFront = falsevar isExternal = falsevar isUnknow = falsefor (cameraInfo in cameraInfos) {when (cameraInfo.lensFacing) {CameraSelector.LENS_FACING_FRONT -> {isSupportFront = truetextC += "\n前置 lensFacing:[${cameraInfo.lensFacing},${cameraInfo.cameraSelector}]"}CameraSelector.LENS_FACING_BACK -> {isSupportBack = truetextC += "\n后置 lensFacing:[${cameraInfo.lensFacing},${cameraInfo.cameraSelector}]"}CameraSelector.LENS_FACING_EXTERNAL -> {isExternal = truetextC += "\n外置 lensFacing:[${cameraInfo.lensFacing},${cameraInfo.cameraSelector}]"}CameraSelector.LENS_FACING_UNKNOWN -> {isUnknow = truetextC += "\n未知 lensFacing:[${cameraInfo.lensFacing},${cameraInfo.cameraSelector}]"}}}LogUtils.logI("init","设备支持情况：后置:${isSupportBack},前置:${isSupportFront},外置:${isExternal},未知:${isUnknow}")binding.tvCheckResult.text = "len:$textC\n" +"设备支持情况：后置:${isSupportBack},前置:${isSupportFront},外置:${isExternal},未知:${isUnknow}"}, ContextCompat.getMainExecutor(this))

工业平板做的产品摄像头一般固定获取之后指定即可，也可以自己编辑优先级逻辑，下面是插两个摄像头的例子

可以使用上述打印的具体摄像头（推荐） 也可以自己bulid，自己build有局限性比如两个外置，你使用2去build就不行了

        val selector: CameraSelector = if (isSupportBack) {CameraSelector.DEFAULT_BACK_CAMERA} else if (isSupportFront) {CameraSelector.DEFAULT_FRONT_CAMERA} else if (isExternal) {CameraSelector.Builder().requireLensFacing(2).build()} else if (isUnknow) {CameraSelector.Builder().requireLensFacing(1).build()} else {CameraSelector.DEFAULT_BACK_CAMERA}

// 如果你使用的是surfaceview+cameraId 而且是多预览 

   val cameraManager =activity.getSystemService(AppCompatActivity.CAMERA_SERVICE) as CameraManagerval cameraIds = cameraManager.cameraIdListfor (cameraId in cameraIds) {val characteristics = cameraManager.getCameraCharacteristics(cameraId)val facing = characteristics.get(CameraCharacteristics.LENS_FACING)}

明确了cameraId 其他通过预览的示例代码 我也传一下吧，由于每个摄像头是独立 有多少个预览就new多少个出来 

class CameraUtils {val TAG = "CameraUtils"private var mCameraDevice: CameraDevice? = nullprivate var mCaptureSession: CameraCaptureSession? = nullprivate var mPreviewBuilder: CaptureRequest.Builder? = nullfun bindSurfaceView(activity: Activity,surfaceView: SurfaceView,len: Int,cId: String?): String {val cameraManager =activity.getSystemService(AppCompatActivity.CAMERA_SERVICE) as CameraManagersurfaceView.holder.setFixedSize(9999, 9999)LogUtils.logI(TAG, "bindSurfaceView")val cameraId = cId ?: getCameraId(cameraManager, len)try {LogUtils.log("len:$len cameraId:$cameraId")if (TextUtils.isEmpty(cameraId)) {LogUtils.logE(TAG, "cameraId  null")return "cameraId  null"}if (ActivityCompat.checkSelfPermission(activity,Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {LogUtils.logE(TAG, "没有权限")return "没有权限"}cameraManager.openCamera(cameraId!!, object : CameraDevice.StateCallback() {override fun onOpened(camera: CameraDevice) {LogUtils.logE(TAG, "onOpened cameraId:$cameraId")mCameraDevice = cameracreateCaptureSession(camera, surfaceView)}override fun onDisconnected(camera: CameraDevice) {LogUtils.logE(TAG, "onDisconnected cameraId:$cameraId")}override fun onError(camera: CameraDevice, error: Int) {LogUtils.logE(TAG, "onError:$error cameraId:$cameraId")}}, null)} catch (e: CameraAccessException) {e.printStackTrace()LogUtils.logE(TAG, "onError:$e")return "onError:$e"}return "cameraId:$cameraId"}/*** 创建CaptureSession*/private fun createCaptureSession(camera: CameraDevice, surfaceView: SurfaceView) {try {surfaceView.run {val surfaceHolder: SurfaceHolder = getHolder()surfaceHolder.setFixedSize(getWidth(), getHeight())val surfaces: MutableList<Surface> = ArrayList()surfaces.add(surfaceHolder.surface)mPreviewBuilder = camera.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW)mPreviewBuilder?.addTarget(surfaceHolder.surface)camera.createCaptureSession(surfaces,object : CameraCaptureSession.StateCallback() {override fun onConfigured(session: CameraCaptureSession) {mCaptureSession = sessionupdatePreview()}override fun onConfigureFailed(session: CameraCaptureSession) {// 配置会话失败}},null)}} catch (e: CameraAccessException) {e.printStackTrace()}}private fun updatePreview() {if (mCameraDevice == null) {LogUtils.logE(TAG, "mCameraDevice null")return}if (mCaptureSession == null) {LogUtils.logE(TAG, "mCaptureSession null")return}if (mPreviewBuilder == null) {LogUtils.logE(TAG, "mPreviewBuilder null")return}LogUtils.logI(TAG, "updatePreview.")try {mCaptureSession?.setRepeatingRequest(mPreviewBuilder!!.build(), null, null)} catch (e: Exception) {e.printStackTrace()LogUtils.logE(TAG, "updatePreview: $e")}}@Throws(CameraAccessException::class)private fun getCameraId(cameraManager: CameraManager, len: Int): String? {val cameraIds = cameraManager.cameraIdListfor (cameraId in cameraIds) {val characteristics = cameraManager.getCameraCharacteristics(cameraId)val facing = characteristics.get(CameraCharacteristics.LENS_FACING)//            CameraCharacteristics.LENS_FACING_BACK CameraCharacteristics.LENS_FACING_FRONTif (facing != null && facing == len) {return cameraId}}return null}}

比如用RecyclerView 多个item预览  可以这样初始化

    fun getOneUtils(index: Int): CameraUtils {var cache = mCameraUnitsMap[index]if (cache == null) {cache = CameraUtils()mCameraUnitsMap[index] = cache}return cache}

使用

   val text = getOneUtils(position).bindSurfaceView(this@CameraInfoActivity,holder.getView(R.id.surfaceView),len, cameraId)

如果是uniapp同学需要买相关插件的可以留言联系