使用Camera2，让相机功能更灵活

Camera2介绍

Camera2 API是Android系统中用于访问相机功能的一套API。它提供了更强大和灵活的相机控制能力，相比之前的Camera API，Camera2 API支持更多的功能和更高的性能。

使用Camera2 API，开发者可以实现更多的相机功能，如手动对焦、手动曝光、原生RAW图像捕获等。同时，Camera2 API也提供了更好的性能和更低的延迟，使得相机应用在性能要求较高的场景下能够更好地发挥作用。

在Android系统中，相机功能的实现离不开Camera2 API的支持，因此对于需要使用相机功能的应用开发者来说，熟悉并掌握Camera2 API是非常重要的。

Camera2主要包括以下几个重要组件：

CameraManager：相机管理器，用于检测和连接可用的相机设备。
CameraDevice：相机设备，代表一个物理相机设备，可以打开、配置和关闭相机设备。
CameraCaptureSession：相机捕获会话，用于发送捕获请求和接收捕获结果，可以预览、拍照、录像等。
CameraCharacteristics：相机特性，提供了相机设备的静态信息，如支持的参数、分辨率、对焦模式等。

使用Camera2，开发者可以更灵活地控制相机的功能和参数，实现更丰富的相机应用程序。

Camera2使用

检查相机权限：确保在AndroidManifest.xml文件中添加了相机权限

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

设置相机预览

创建一个TextureView用于显示相机预览画面。
使用CameraManager获取相机设备的ID，并打开相机。
创建CameraCaptureSession用于预览。

拍照

创建一个按钮用于触发拍照操作。
当用户点击按钮时，使用CameraCaptureSession进行拍照操作。
保存拍摄的照片到指定的文件路径。

处理相机权限和生命周期

在onResume方法中检查相机权限，并打开相机。
在onPause方法中关闭相机，释放相关资源。

示例代码：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextureView
        android:id="@+id/textureView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1"/>

    <Button
        android:onClick="takePicture"
        android:id="@+id/btnCapture" 
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:text="拍照"/>
</LinearLayout>

public class CameraActivity extends AppCompatActivity {

    private static final int REQUEST_CAMERA_PERMISSION = 200;
    private static final int REQUEST_WRITE_EXTERNAL_STORAGE_PERMISSION = 201;

    private CameraManager cameraManager;
    private String cameraId;
    private CameraDevice cameraDevice;
    private CameraCaptureSession cameraCaptureSession;
    private CaptureRequest.Builder captureRequestBuilder;
    private ImageReader imageReader;

    private TextureView textureView;

    private final TextureView.SurfaceTextureListener surfaceTextureListener = new TextureView.SurfaceTextureListener() {
        @Override
        public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {
            openCamera();
        }

        @Override
        public void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) {
        }

        @Override
        public boolean onSurfaceTextureDestroyed(SurfaceTexture surface) {
            return false;
        }

        @Override
        public void onSurfaceTextureUpdated(SurfaceTexture surface) {
        }
    };

    private final CameraDevice.StateCallback stateCallback = new CameraDevice.StateCallback() {
        @Override
        public void onOpened(@NonNull CameraDevice camera) {
            cameraDevice = camera;
            createCameraPreview();
        }

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

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

    private final CameraCaptureSession.StateCallback captureSessionStateCallback = new CameraCaptureSession.StateCallback() {
        @Override
        public void onConfigured(@NonNull CameraCaptureSession session) {
            cameraCaptureSession = session;
            try {
                captureRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
                cameraCaptureSession.setRepeatingRequest(captureRequestBuilder.build(), null, null);
            } catch (CameraAccessException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onConfigureFailed(@NonNull CameraCaptureSession session) {
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_camera);

        textureView = findViewById(R.id.textureView);
        
        textureView.setSurfaceTextureListener(surfaceTextureListener);
    }

    @Override
    protected void onResume() {
        super.onResume();
        if (textureView.isAvailable()) {
            openCamera();
        } else {
            textureView.setSurfaceTextureListener(surfaceTextureListener);
        }
    }

    @Override
    protected void onPause() {
        closeCamera();
        super.onPause();
    }

    private void openCamera() {
        cameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
        try {
            cameraId = cameraManager.getCameraIdList()[0];
            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.CAMERA}, REQUEST_CAMERA_PERMISSION);
                return;
            }
            cameraManager.openCamera(cameraId, stateCallback, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    private void createCameraPreview() {
        SurfaceTexture texture = textureView.getSurfaceTexture();
        texture.setDefaultBufferSize(textureView.getWidth(), textureView.getHeight());
        Surface surface = new Surface(texture);
        try {
            captureRequestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
            captureRequestBuilder.addTarget(surface);
            cameraDevice.createCaptureSession(Collections.singletonList(surface), captureSessionStateCallback, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    private void closeCamera() {
        if (cameraCaptureSession != null) {
            cameraCaptureSession.close();
            cameraCaptureSession = null;
        }
        if (cameraDevice != null) {
            cameraDevice.close();
            cameraDevice = null;
        }
    }

    public void takePicture() {
        if (cameraDevice == null) {
            return;
        }
        CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
        try {
            CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraDevice.getId());
            Size[] jpegSizes = null;
            if (characteristics != null) {
                jpegSizes = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP).getOutputSizes(ImageFormat.JPEG);
            }
            int width = 640;
            int height = 480;
            if (jpegSizes != null && jpegSizes.length > 0) {
                width = jpegSizes[0].getWidth();
                height = jpegSizes[0].getHeight();
            }
            ImageReader reader = ImageReader.newInstance(width, height, ImageFormat.JPEG, 1);
            List<Surface> outputSurfaces = new ArrayList<>(2);
            outputSurfaces.add(reader.getSurface());
            outputSurfaces.add(new Surface(textureView.getSurfaceTexture()));

            CaptureRequest.Builder captureBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
            captureBuilder.addTarget(reader.getSurface());
            captureBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);

            int rotation = getWindowManager().getDefaultDisplay().getRotation();
            captureBuilder.set(CaptureRequest.JPEG_ORIENTATION, ORIENTATIONS.get(rotation));

            File file = new File(getExternalFilesDir(null), "pic.jpg");
            ImageReader.OnImageAvailableListener readerListener = new ImageReader.OnImageAvailableListener() {
                @Override
                public void onImageAvailable(ImageReader reader) {
                    Image image = null;
                    try {
                        image = reader.acquireLatestImage();
                        ByteBuffer buffer = image.getPlanes()[0].getBuffer();
                        byte[] bytes = new byte[buffer.capacity()];
                        buffer.get(bytes);
                        save(bytes);
                    } catch (FileNotFoundException e) {
                        e.printStackTrace();
                    } catch (IOException e) {
                        e.printStackTrace();
                    } finally {
                        if (image != null) {
                            image.close();
                        }
                    }
                }

                private void save(byte[] bytes) throws IOException {
                    OutputStream output = null;
                    try {
                        output = new FileOutputStream(file);
                        output.write(bytes);
                    } finally {
                        if (output != null) {
                            output.close();
                        }
                    }
                }
            };

            reader.setOnImageAvailableListener(readerListener, null);

            final CameraCaptureSession.CaptureCallback captureListener = new CameraCaptureSession.CaptureCallback() {
                @Override
                public void onCaptureCompleted(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
                    super.onCaptureCompleted(session, request, result);
                    Toast.makeText(CameraActivity.this, "Saved:" + file, Toast.LENGTH_SHORT).show();
                    createCameraPreview();
                }
            };

            cameraDevice.createCaptureSession(outputSurfaces, new CameraCaptureSession.StateCallback() {
                @Override
                public void onConfigured(@NonNull CameraCaptureSession session) {
                    try {
                        session.capture(captureBuilder.build(), captureListener, null);
                    } catch (CameraAccessException e) {
                        e.printStackTrace();
                    }
                }

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