如何在Android中以编程方式(无布局)获得camera2预览帧？

在Android中以编程方式获取Camera2预览帧，可以通过以下步骤实现：

首先，需要在AndroidManifest.xml文件中添加相机权限：

<uses-permission android:name="android.permission.CAMERA" />

创建一个CameraManager对象，用于管理相机设备：

CameraManager cameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);

获取可用的相机设备列表，并选择一个相机设备：

String cameraId = null;
try {
    String[] cameraIds = cameraManager.getCameraIdList();
    cameraId = cameraIds[0]; // 选择第一个相机设备
} catch (CameraAccessException e) {
    e.printStackTrace();
}

打开相机设备，并设置相机状态回调：

CameraDevice cameraDevice = null;
try {
    cameraManager.openCamera(cameraId, new CameraDevice.StateCallback() {
        @Override
        public void onOpened(@NonNull CameraDevice camera) {
            cameraDevice = camera;
            // 相机打开成功后进行后续操作
        }

        @Override
        public void onDisconnected(@NonNull CameraDevice camera) {
            cameraDevice.close();
            cameraDevice = null;
        }

        @Override
        public void onError(@NonNull CameraDevice camera, int error) {
            cameraDevice.close();
            cameraDevice = null;
        }
    }, null);
} catch (CameraAccessException e) {
    e.printStackTrace();
}

创建一个CameraCaptureSession对象，用于预览相机图像：

List<Surface> surfaces = new ArrayList<>();
SurfaceTexture surfaceTexture = new SurfaceTexture(0); // 创建一个SurfaceTexture对象
Surface previewSurface = new Surface(surfaceTexture);
surfaces.add(previewSurface);

cameraDevice.createCaptureSession(surfaces, new CameraCaptureSession.StateCallback() {
    @Override
    public void onConfigured(@NonNull CameraCaptureSession session) {
        // 配置成功后进行后续操作
        CaptureRequest.Builder captureRequestBuilder;
        try {
            captureRequestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
            captureRequestBuilder.addTarget(previewSurface);

            session.setRepeatingRequest(captureRequestBuilder.build(), null, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onConfigureFailed(@NonNull CameraCaptureSession session) {
        // 配置失败处理
    }
}, null);

在预览回调中获取相机预览帧：

cameraDevice.createCaptureSession(surfaces, new CameraCaptureSession.StateCallback() {
    @Override
    public void onConfigured(@NonNull CameraCaptureSession session) {
        // 配置成功后进行后续操作
        CaptureRequest.Builder captureRequestBuilder;
        try {
            captureRequestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
            captureRequestBuilder.addTarget(previewSurface);

            session.setRepeatingRequest(captureRequestBuilder.build(), new CameraCaptureSession.CaptureCallback() {
                @Override
                public void onCaptureCompleted(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
                    // 在这里处理预览帧数据
                    Image image = result.get(CaptureResult.STATISTICS_PREVIEW);
                    ByteBuffer buffer = image.getPlanes()[0].getBuffer();
                    byte[] data = new byte[buffer.remaining()];
                    buffer.get(data);
                    // 对预览帧数据进行处理
                }
            }, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onConfigureFailed(@NonNull CameraCaptureSession session) {
        // 配置失败处理
    }
}, null);

通过以上步骤，你可以在Android中以编程方式获取Camera2预览帧。请注意，以上代码仅为示例，实际使用时需要进行适当的错误处理和资源释放。