android.hardware.camera2 使用指南

API 21中將原來的 camera API 棄用轉而推薦使用新增的 camera2 API，這是一個大的動做，由於新 API 換了架構，讓開發者用起來更難了。

先來看看 camera2包架構示意圖：

這裏引用了管道的概念將安卓設備和攝像頭之間聯通起來，系統向攝像頭髮送 Capture 請求，而攝像頭會返回 CameraMetadata。這一切創建在一個叫做 CameraCaptureSession 的會話中。

下面是 camera2包中的主要類：

其中 CameraManager 是那個站在高處統管全部攝像投設備（CameraDevice）的管理者，而每一個 CameraDevice 本身會負責創建 CameraCaptureSession 以及創建 CaptureRequest。

CameraCharacteristics 是 CameraDevice 的屬性描述類，非要作個對比的話，那麼它與原來的 CameraInfo 有類似性。

類圖中有着三個重要的 callback，雖然這增長了閱讀代碼的難度，可是你必需要習慣，由於這是新包的風格。其中 CameraCaptureSession.CaptureCallback 將處理預覽和拍照圖片的工做，須要重點對待。

這些類是如何相互配合的？下面是簡單的流程圖。

我是用 SurfaceView 做爲顯示對象（固然還能夠 TextureView 去顯示，詳見參考中的項目）

核心代碼以下：

mCameraManager = (CameraManager) this.getSystemService(Context.CAMERA_SERVICE);
        mSurfaceView = (SurfaceView)findViewById(R.id.surfaceview);
        mSurfaceHolder = mSurfaceView.getHolder();
        mSurfaceHolder.addCallback(new SurfaceHolder.Callback() {
            @Override
            public void surfaceCreated(SurfaceHolder holder) {
                initCameraAndPreview();
            }
        });

private void initCameraAndPreview() {
            Log.d("linc","init camera and preview");
            HandlerThread handlerThread = new HandlerThread("Camera2");
            handlerThread.start();
            mHandler = new Handler(handlerThread.getLooper());
            try {
                mCameraId = ""+CameraCharacteristics.LENS_FACING_FRONT;
                mImageReader = ImageReader.newInstance(mSurfaceView.getWidth(), mSurfaceView.getHeight(),
                        ImageFormat.JPEG,/*maxImages*/7);
                mImageReader.setOnImageAvailableListener(mOnImageAvailableListener, mHandler);

                mCameraManager.openCamera(mCameraId, DeviceStateCallback, mHandler);
            } catch (CameraAccessException e) {
                Log.e("linc", "open camera failed." + e.getMessage());
            }
        }

private CameraDevice.StateCallback DeviceStateCallback = new CameraDevice.StateCallback() {

            @Override
            public void onOpened(CameraDevice camera) {
                Log.d("linc","DeviceStateCallback:camera was opend.");
                mCameraOpenCloseLock.release();
                mCameraDevice = camera;
                try {
                    createCameraCaptureSession();
                } catch (CameraAccessException e) {
                    e.printStackTrace();
                }
            }
        };

private void createCameraCaptureSession() throws CameraAccessException {
            Log.d("linc","createCameraCaptureSession");

            mPreviewBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
            mPreviewBuilder.addTarget(mSurfaceHolder.getSurface());
            mState = STATE_PREVIEW;
            mCameraDevice.createCaptureSession(
                    Arrays.asList(mSurfaceHolder.getSurface(), mImageReader.getSurface()),
                    mSessionPreviewStateCallback, mHandler);
        }

private CameraCaptureSession.StateCallback mSessionPreviewStateCallback = new
                CameraCaptureSession.StateCallback() {

            @Override
            public void onConfigured(CameraCaptureSession session) {
                Log.d("linc","mSessionPreviewStateCallback onConfigured");
                mSession = session;
                try {
                    mPreviewBuilder.set(CaptureRequest.CONTROL_AF_MODE,
                          CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
                    mPreviewBuilder.set(CaptureRequest.CONTROL_AE_MODE,
                           CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH);
                    session.setRepeatingRequest(mPreviewBuilder.build(), mSessionCaptureCallback, mHandler);
                } catch (CameraAccessException e) {
                    e.printStackTrace();
                    Log.e("linc","set preview builder failed."+e.getMessage());
                }
            }
        };

private CameraCaptureSession.CaptureCallback mSessionCaptureCallback =
                new CameraCaptureSession.CaptureCallback() {

            @Override
            public void onCaptureCompleted(CameraCaptureSession session, CaptureRequest request,
                                           TotalCaptureResult result) {
    //            Log.d("linc","mSessionCaptureCallback, onCaptureCompleted");
                mSession = session;
                checkState(result);
            }

            @Override
            public void onCaptureProgressed(CameraCaptureSession session, CaptureRequest request,
                                            CaptureResult partialResult) {
                Log.d("linc","mSessionCaptureCallback,  onCaptureProgressed");
                mSession = session;
                checkState(partialResult);
            }

            private void checkState(CaptureResult result) {
                switch (mState) {
                    case STATE_PREVIEW:
                        // NOTHING
                        break;
                    case STATE_WAITING_CAPTURE:
                        int afState = result.get(CaptureResult.CONTROL_AF_STATE);

                        if (CaptureResult.CONTROL_AF_STATE_FOCUSED_LOCKED == afState ||
                             CaptureResult.CONTROL_AF_STATE_NOT_FOCUSED_LOCKED == afState
                                ||  CaptureResult.CONTROL_AF_STATE_PASSIVE_FOCUSED == afState
                                || CaptureResult.CONTROL_AF_STATE_PASSIVE_UNFOCUSED == afState) {
                            //do something like save picture
                        }
                        break;
                }
            }

        };

按下 capture 按鈕：

public void onCapture(View view) {
        try {
            Log.i("linc", "take picture");
            mState = STATE_WAITING_CAPTURE;
            mSession.setRepeatingRequest(mPreviewBuilder.build(), mSessionCaptureCallback, mHandler);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

測試用 genemotion 模擬器，直接調用筆記本的攝像頭。

配置圖以下：

demo 界面以下圖：

源碼：