如何在camera 2 api片段中捕获并预览显示到图像视图？

要在Camera 2 API片段中捕获并预览显示到图像视图，你需要遵循以下步骤：

基础概念

Camera 2 API是Android提供的一个用于控制相机硬件的接口，它提供了比Camera API更强大的功能和更细粒度的控制。

类型

预览：实时显示相机捕获的图像。
拍照：捕获单张静态图像。
录像：录制视频。

应用场景

实时监控：如安防摄像头应用。
专业摄影：如相机应用中的手动模式。
增强现实：实时图像处理和叠加。

实现步骤

设置权限：确保应用有相机和存储权限。
创建CameraManager：用于管理相机设备。
打开相机：选择一个相机设备并打开它。
配置预览会话：设置预览的分辨率和其他参数。
显示预览：将捕获的图像显示到ImageView中。

示例代码

以下是一个简化的示例代码，展示了如何在Camera 2 API中设置预览并显示到ImageView：

public class CameraPreviewFragment extends Fragment {
    private CameraDevice cameraDevice;
    private CameraCaptureSession captureSession;
    private ImageReader imageReader;
    private SurfaceTexture surfaceTexture;
    private ImageView imageView;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_camera_preview, container, false);
        imageView = view.findViewById(R.id.imageView);
        return view;
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        SurfaceView surfaceView = view.findViewById(R.id.surfaceView);
        surfaceTexture = new SurfaceTexture(10);
        surfaceView.getHolder().addCallback(new SurfaceHolder.Callback() {
            @Override
            public void surfaceCreated(SurfaceHolder holder) {
                openCamera();
            }

            @Override
            public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {}

            @Override
            public void surfaceDestroyed(SurfaceHolder holder) {}
        });
    }

    private void openCamera() {
        CameraManager manager = (CameraManager) getActivity().getSystemService(Context.CAMERA_SERVICE);
        try {
            String cameraId = manager.getCameraIdList()[0];
            CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
            StreamConfigurationMap map = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
            Size[] outputSizes = map.getOutputSizes(SurfaceTexture.class);
            Size chosenSize = outputSizes[0]; // Choose the smallest size for preview

            manager.openCamera(cameraId, new CameraDevice.StateCallback() {
                @Override
                public void onOpened(@NonNull CameraDevice camera) {
                    cameraDevice = camera;
                    createCameraPreviewSession();
                }

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

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

    private void createCameraPreviewSession() {
        try {
            Surface surface = new Surface(surfaceTexture);
            captureRequestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
            captureRequestBuilder.addTarget(surface);

            cameraDevice.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback() {
                @Override
                public void onConfigured(@NonNull CameraCaptureSession session) {
                    if (cameraDevice == null) return;
                    captureSession = session;
                    updatePreview();
                }

                @Override
                public void onConfigureFailed(@NonNull CameraCaptureSession session) {}
            }, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    private void updatePreview() {
        if (cameraDevice == null) return;
        captureRequestBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
        try {
            captureSession.setRepeatingRequest(captureRequestBuilder.build(), null, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    // Handle image capture and display to imageView
    private ImageReader.OnImageAvailableListener imageAvailableListener = new ImageReader.OnImageAvailableListener() {
        @Override
        public void onImageAvailable(ImageReader reader) {
            Image image = null;
            try {
                image = reader.acquireLatestImage();
                if (image != null) {
                    ByteBuffer buffer = image.getPlanes()[0].getBuffer();
                    byte[] bytes = new byte[buffer.remaining()];
                    buffer.get(bytes);
                    Bitmap bitmap = BitmapFactory.decodeByteArray(bytes, 0, bytes.length);
                    imageView.setImageBitmap(bitmap);
                }
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                if (image != null) {
                    image.close();
                }
            }
        }
    };

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        if (cameraDevice != null) {
            cameraDevice.close();
        }
        if (captureSession != null) {
            captureSession.close();
        }
        if (imageReader != null) {
            imageReader.close();
        }
    }
}