android.hardware.camera2使用指南

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API 21中将原来的camera API弃用转而推荐使用新增的camera2 API，这是一个大的动作，因为新API换了架构，让开发者用起来更难了。
先来看看camera2包架构示意图：
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这里引用了管道的概念将安卓设备和摄像头之间联通起来，系统向摄像头发送Capture请求，而摄像头会返回CameraMetadata。这一切建立在一个叫作CameraCaptureSession的会话中。

下面是camera2包中的主要类：
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其中CameraManager是那个站在高处统管所有摄像投设备（CameraDevice）的管理者，而每个CameraDevice自己会负责建立CameraCaptureSession以及建立CaptureRequest。CameraCharacteristics是CameraDevice的属性描述类，非要做个对比的话，那么它与原来的CameraInfo有相似性。
类图中有着三个重要的callback，虽然这增加了阅读代码的难度，但是你必须要习惯，因为这是新包的风格。其中CameraCaptureSession.CaptureCallback将处理预览和拍照图片的工作，需要重点对待。

这些类是如何相互配合的？下面是简单的流程图。
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我是用SurfaceView作为显示对象（当然还可以TextureView去显示，详见参考中的项目）
核心代码如下：

        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按钮：

    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();        }    }

测试用genemotion模拟器，直接调用笔记本的摄像头。
配置图如下：
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demo界面如下图：
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