相机开启时调用Torch触发CameraAccessException问题求助

问题原因 #

当应用内启动相机并创建了预览会话（无论是Camera2还是旧Camera API），相机硬件资源（包括闪光灯）会被当前活跃的相机会话独占。此时再通过CameraManager.setTorchMode()操作闪光灯，就会触发CAMERA_IN_USE异常——因为Torch属于相机硬件的一部分，已被活跃会话占用，无法被CameraManager直接访问。

解决方案 #

需要根据相机的使用方式，分两种场景处理闪光灯控制：

场景1：使用Camera2 API管理相机 #

重构FlashLight类，让它支持绑定活跃的相机会话，通过CaptureRequest控制闪光灯状态，而不是直接调用CameraManager：

class FlashLight(private val context: Context) {
    private val cameraManager by lazy { context.getSystemService(Context.CAMERA_SERVICE) as CameraManager }
    private val backCameraId by lazy { cameraManager.cameraIdList[0] }
    private var cameraCaptureSession: CameraCaptureSession? = null
    private var cameraDevice: CameraDevice? = null

    // 绑定活跃的相机会话，在相机打开并创建会话后调用
    fun attachCameraSession(session: CameraCaptureSession, device: CameraDevice) {
        cameraCaptureSession = session
        cameraDevice = device
    }

    fun turnOnFlashLight() {
        // 优先通过相机会话控制闪光灯
        cameraCaptureSession?.let { session ->
            try {
                val requestBuilder = cameraDevice?.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW) ?: return
                // 关闭自动曝光，强制闪光灯常亮
                requestBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_OFF)
                requestBuilder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_TORCH)
                session.setRepeatingRequest(requestBuilder.build(), null, null)
            } catch (e: Exception) {
                L.e(e)
            }
            return
        }
        // 相机未活跃时，使用原CameraManager方式
        changeFlashStatus(true)
    }

    fun turnOffFlashLight() {
        cameraCaptureSession?.let { session ->
            try {
                val requestBuilder = cameraDevice?.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW) ?: return
                // 恢复自动曝光，关闭闪光灯
                requestBuilder.set(CaptureRequest.CONTROL_AE_MODE, CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH)
                requestBuilder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_OFF)
                session.setRepeatingRequest(requestBuilder.build(), null, null)
            } catch (e: Exception) {
                L.e(e)
            }
            return
        }
        changeFlashStatus(false)
    }

    private fun changeFlashStatus(shouldBeTurnedOn: Boolean) {
        try {
            cameraManager.setTorchMode(backCameraId, shouldBeTurnedOn)
        } catch (e: Exception) {
            L.e(e)
        }
    }

    // 相机释放时调用，清空会话引用
    fun detachCameraSession() {
        cameraCaptureSession = null
        cameraDevice = null
    }
}

使用说明

在相机初始化流程中，创建完CameraCaptureSession后，调用flashLight.attachCameraSession(session, cameraDevice)绑定会话；相机释放时调用flashLight.detachCameraSession()。

场景2：使用旧Camera API（android.hardware.Camera） #

如果应用使用的是旧版Camera API，直接通过Camera.Parameters控制闪光灯：

class FlashLight(private val context: Context) {
    private val cameraManager by lazy { context.getSystemService(Context.CAMERA_SERVICE) as CameraManager }
    private val backCameraId by lazy { cameraManager.cameraIdList[0] }
    private var camera: android.hardware.Camera? = null

    fun attachCamera(cameraInstance: android.hardware.Camera) {
        camera = cameraInstance
    }

    fun turnOnFlashLight() {
        camera?.let { cam ->
            try {
                val params = cam.parameters
                params.flashMode = android.hardware.Camera.Parameters.FLASH_MODE_TORCH
                cam.parameters = params
            } catch (e: Exception) {
                L.e(e)
            }
            return
        }
        changeFlashStatus(true)
    }

    fun turnOffFlashLight() {
        camera?.let { cam ->
            try {
                val params = cam.parameters
                params.flashMode = android.hardware.Camera.Parameters.FLASH_MODE_OFF
                cam.parameters = params
            } catch (e: Exception) {
                L.e(e)
            }
            return
        }
        changeFlashStatus(false)
    }

    private fun changeFlashStatus(shouldBeTurnedOn: Boolean) {
        try {
            cameraManager.setTorchMode(backCameraId, shouldBeTurnedOn)
        } catch (e: Exception) {
            L.e(e)
        }
    }

    fun detachCamera() {
        camera = null
    }
}

注意事项 #

1. 确保已在Manifest中添加必要权限：

   <uses-permission android:name="android.permission.CAMERA" />
   <uses-permission android:name="android.permission.FLASHLIGHT" />
   <uses-feature android:name="android.hardware.camera" />
   <uses-feature android:name="android.hardware.camera.flash" />
   

2. 动态申请CAMERA权限（Android 6.0及以上），否则无法访问相机及闪光灯资源。

内容的提问来源于stack exchange，提问作者Wafi_ck