：多个前置摄像头之间的切换

Question

我正在尝试编写我的第一个Android摄像头应用程序，但它总是选择变焦相机而不是主摄像头。(我在华为P30 Pro上进行了测试)

代码基于官方的camerax示例应用程序(https://github.com/android/camera-samples/tree/master/CameraXBasic)。

有关守则：

/** Declare and bind preview, capture and analysis use cases */
private fun bindCameraUseCases() {

    // Get screen metrics used to setup camera for full screen resolution
    val metrics = DisplayMetrics().also { viewFinder.display.getRealMetrics(it) }
    Log.d(TAG, "Screen metrics: ${metrics.widthPixels} x ${metrics.heightPixels}")

    val screenAspectRatio = aspectRatio(metrics.widthPixels, metrics.heightPixels)
    Log.d(TAG, "Preview aspect ratio: $screenAspectRatio")

    val rotation = viewFinder.display.rotation

    // Bind the CameraProvider to the LifeCycleOwner

    val cameraSelector = CameraSelector.Builder().requireLensFacing(lensFacing).build()

    val cameraProviderFuture = ProcessCameraProvider.getInstance(requireContext())
    cameraProviderFuture.addListener(Runnable {

        // CameraProvider
        val cameraProvider: ProcessCameraProvider = cameraProviderFuture.get()

        // Preview
        preview = Preview.Builder()
            // We request aspect ratio but no resolution
            .setTargetAspectRatio(screenAspectRatio)
            // Set initial target rotation
            .setTargetRotation(rotation)
            .build()

        // ImageCapture
        imageCapture = ImageCapture.Builder()
            .setCaptureMode(ImageCapture.CAPTURE_MODE_MINIMIZE_LATENCY)
            // We request aspect ratio but no resolution to match preview config, but letting
            // CameraX optimize for whatever specific resolution best fits our use cases
            .setTargetAspectRatio(screenAspectRatio)
            // Set initial target rotation, we will have to call this again if rotation changes
            // during the lifecycle of this use case
            .setTargetRotation(rotation)
            .build()

        // Must unbind the use-cases before rebinding them
        cameraProvider.unbindAll()

        try {
            // A variable number of use-cases can be passed here -
            // camera provides access to CameraControl & CameraInfo
            camera = cameraProvider.bindToLifecycle(
                    this, cameraSelector, preview, imageCapture /**, imageAnalyzer*/)

            // Attach the viewfinder's surface provider to preview use case
            preview?.setSurfaceProvider(viewFinder.createSurfaceProvider(camera?.cameraInfo))
        } catch(exc: Exception) {
            Log.e(TAG, "Use case binding failed", exc)
        }

    }, ContextCompat.getMainExecutor(requireContext()))
}

Answer 1

使用当前的CameraX API，我不认为您可以选择使用哪个特定的相机，您只能选择镜头面对(CameraSelector.Builder().requireLensFacing(int)，它可以是正面或背面。当您绑定用例时，CameraX会选择满足用例需求的第一个摄像机。例如，当将预览用例绑定到已启用和禁用的扩展时，可能会使用两个不同的背靠背摄像机。

CameraSelector API似乎仍然有发展的空间，所以在未来，您可能对选择哪个摄像机有更多的控制。如果您现在需要这种控制，您可能需要使用Camera2。

Answer 2

你可以通过设置cameraSelector来改变相机。例如，要用index=2设置相机，请使用以下代码。

List<CameraInfo> availableCameraInfos = cameraProvider.getAvailableCameraInfos();
Log.i(TAG, "[startCamera] available cameras:"+availableCameraInfos);
    
// Select back camera as a default
//CameraSelector cameraSelector = CameraSelector.DEFAULT_BACK_CAMERA;
CameraSelector cameraSelector = availableCameraInfos.get(2).getCameraSelector();

Answer 3

我也有类似的问题，但后面的摄像头。我检查了一些设备，发现在所有测试的设备上，我可以选择相机id并获得正确的照相机：

• 相机ID "0“->法线/默认后向相机
• 照相机ID "1”->普通/默认前向摄像机

因此，我创建了一个自定义的CameraFilter，在其中筛选相机id "0"：

class CameraIdFilter(private val cameraId: String) : CameraFilter {

override fun filterCameras(cameras: Set<CameraInternal>): Set<CameraInternal> {
    val resultCameras: MutableSet<CameraInternal> = LinkedHashSet()
    for (camera in cameras) {
        val cameraId = camera.cameraInfoInternal.cameraId
        if (cameraId == this.cameraId) {
            resultCameras.add(camera)
        }
    }
    return resultCameras
}

}

并将过滤器附加到相机选择器：

        val cameraSelectorBuilder = CameraSelector.Builder()
            .requireLensFacing(lensFacing)
            .appendFilter(CameraIdFilter("0"))

我不建议在生产应用程序中使用这个，因为我确信有些设备不遵循这种约定/模式。但是，您可以在内部应用程序中使用它，在该应用程序中，您可以知道用户使用的设备。