@Override
public void onViewCreated(final View view, Bundle savedInstanceState) {
    view.findViewById(R.id.picture).setOnClickListener(this);
    view.findViewById(R.id.info).setOnClickListener(this);
    mTextureView = (AutoFitTextureView) view.findViewById(R.id.texture);//获取mTextureView
}

...

 @Override
    public void onResume() {
        super.onResume();
        startBackgroundThread();//为相机开启了一个后台线程，这个进程用于后台执行相关的工作
        if (mTextureView.isAvailable()) {//mTextureView已经创建，SurfaceTexture已经有效，则直接openCamera，用于屏幕熄灭等情况，这时onSurfaceTextureAvailable不会回调。
            openCamera(mTextureView.getWidth(), mTextureView.getHeight());
        } else {//SurfaceTexture处于无效状态中，则通过SurfaceTextureListener确保surface准备好。
            mTextureView.setSurfaceTextureListener(mSurfaceTextureListener);//设置mTextureView回调
        }
    }

...

private final TextureView.SurfaceTextureListener mSurfaceTextureListener
            = new TextureView.SurfaceTextureListener() {//TextureView回调

        @Override
        public void onSurfaceTextureAvailable(SurfaceTexture texture, int width, int height) {
            openCamera(width, height);//SurfaceTexture有效即可openCamera,宽高是控件宽高
        }

        @Override
        public void onSurfaceTextureSizeChanged(SurfaceTexture texture, int width, int height) {
            configureTransform(width, height);//配置transformation，主要是矩阵旋转相关
        }

        @Override
        public boolean onSurfaceTextureDestroyed(SurfaceTexture texture) {
            return true;
        }

        @Override
        public void onSurfaceTextureUpdated(SurfaceTexture texture) {
        }

    };

...

 private void setUpCameraOutputs(int width, int height) {////包括对相机设备的选择，ImageReader的初始化和参数、回调设置。设置显示的转化矩阵，即将预览的图片调整至显示图层的大小。
        Activity activity = getActivity();
        CameraManager manager = (CameraManager) activity.getSystemService(Context.CAMERA_SERVICE);
        try {
            for (String cameraId : manager.getCameraIdList()) {//获取摄像头可用列表
                CameraCharacteristics characteristics
                        = manager.getCameraCharacteristics(cameraId);////获取相机的特性

                // We don't use a front facing camera in this sample.
                Integer facing = characteristics.get(CameraCharacteristics.LENS_FACING);// 不使用前置摄像头
                if (facing != null && facing == CameraCharacteristics.LENS_FACING_FRONT) {
                    continue;
                }

                StreamConfigurationMap map = characteristics.get(
                        CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
                if (map == null) {
                    continue;
                }

                // For still image captures, we use the largest available size.
                Size largest = Collections.max(
                        Arrays.asList(map.getOutputSizes(ImageFormat.JPEG)),
                        new CompareSizesByArea());
                mImageReader = ImageReader.newInstance(largest.getWidth(), largest.getHeight(),//相机拍照图像尺寸
                        ImageFormat.JPEG, /*maxImages*/2);//设置ImageReader接收的图片格式，以及允许接收的最大图片数目
                mImageReader.setOnImageAvailableListener(
                        mOnImageAvailableListener, mBackgroundHandler);//设置图片存储的监听，但在创建会话，调用capture后才能有数据

                // Find out if we need to swap dimension to get the preview size relative to sensor
                // coordinate.
                int displayRotation = activity.getWindowManager().getDefaultDisplay().getRotation();//获取显示方向
                //noinspection ConstantConditions
                mSensorOrientation = characteristics.get(CameraCharacteristics.SENSOR_ORIENTATION);//获取sensor方向
                boolean swappedDimensions = false;
                switch (displayRotation) {
                    case Surface.ROTATION_0:
                    case Surface.ROTATION_180:
                        if (mSensorOrientation == 90 || mSensorOrientation == 270) {
                            swappedDimensions = true;
                        }
                        break;
                    case Surface.ROTATION_90:
                    case Surface.ROTATION_270:
                        if (mSensorOrientation == 0 || mSensorOrientation == 180) {
                            swappedDimensions = true;
                        }
                        break;
                    default:
                        Log.e(TAG, "Display rotation is invalid: " + displayRotation);
                }

                Point displaySize = new Point();
                activity.getWindowManager().getDefaultDisplay().getSize(displaySize);
                int rotatedPreviewWidth = width;
                int rotatedPreviewHeight = height;
                int maxPreviewWidth = displaySize.x;
                int maxPreviewHeight = displaySize.y;

                if (swappedDimensions) {//横竖屏交换尺寸
                    rotatedPreviewWidth = height;
                    rotatedPreviewHeight = width;
                    maxPreviewWidth = displaySize.y;
                    maxPreviewHeight = displaySize.x;
                }

                if (maxPreviewWidth > MAX_PREVIEW_WIDTH) {
                    maxPreviewWidth = MAX_PREVIEW_WIDTH;
                }

                if (maxPreviewHeight > MAX_PREVIEW_HEIGHT) {
                    maxPreviewHeight = MAX_PREVIEW_HEIGHT;
                }

                // Danger, W.R.! Attempting to use too large a preview size could  exceed the camera
                // bus' bandwidth limitation, resulting in gorgeous previews but the storage of
                // garbage capture data.
                mPreviewSize = chooseOptimalSize(map.getOutputSizes(SurfaceTexture.class),
                        rotatedPreviewWidth, rotatedPreviewHeight, maxPreviewWidth,
                        maxPreviewHeight, largest);//获取最优的预览分辨率

                // We fit the aspect ratio of TextureView to the size of preview we picked.
                int orientation = getResources().getConfiguration().orientation;
                if (orientation == Configuration.ORIENTATION_LANDSCAPE) {
                    mTextureView.setAspectRatio(
                            mPreviewSize.getWidth(), mPreviewSize.getHeight());
                    //设置TextureView预览分辨率。
                } else {
                    mTextureView.setAspectRatio(
                            mPreviewSize.getHeight(), mPreviewSize.getWidth());
                }

                // Check if the flash is supported.
                //设置闪光灯
                Boolean available = characteristics.get(CameraCharacteristics.FLASH_INFO_AVAILABLE);
                mFlashSupported = available == null ? false : available;

                mCameraId = cameraId;//获取当前ID
                return;
            }
        } catch (CameraAccessException e) {
            e.printStackTrace();
        } catch (NullPointerException e) {
            // Currently an NPE is thrown when the Camera2API is used but not supported on the
            // device this code runs.
            ErrorDialog.newInstance(getString(R.string.camera_error))
                    .show(getChildFragmentManager(), FRAGMENT_DIALOG);
        }
    }

...

 private final ImageReader.OnImageAvailableListener mOnImageAvailableListener
            = new ImageReader.OnImageAvailableListener() {

        @Override
        public void onImageAvailable(ImageReader reader) {//图片有效回调
            mBackgroundHandler.post(new ImageSaver(reader.acquireNextImage(), mFile));//通知ImageSaver线程保存图片，//reader.acquireNextImage()获取图片image
        }

    };

...

 private void configureTransform(int viewWidth, int viewHeight) {//配置transformation，主要是矩阵旋转相关
        Activity activity = getActivity();
        if (null == mTextureView || null == mPreviewSize || null == activity) {
            return;
        }
        int rotation = activity.getWindowManager().getDefaultDisplay().getRotation();
        Matrix matrix = new Matrix();
        RectF viewRect = new RectF(0, 0, viewWidth, viewHeight);
        RectF bufferRect = new RectF(0, 0, mPreviewSize.getHeight(), mPreviewSize.getWidth());
        float centerX = viewRect.centerX();
        float centerY = viewRect.centerY();
        if (Surface.ROTATION_90 == rotation || Surface.ROTATION_270 == rotation) {
            bufferRect.offset(centerX - bufferRect.centerX(), centerY - bufferRect.centerY());
            matrix.setRectToRect(viewRect, bufferRect, Matrix.ScaleToFit.FILL);
            float scale = Math.max(
                    (float) viewHeight / mPreviewSize.getHeight(),
                    (float) viewWidth / mPreviewSize.getWidth());
            matrix.postScale(scale, scale, centerX, centerY);
            matrix.postRotate(90 * (rotation - 2), centerX, centerY);
        } else if (Surface.ROTATION_180 == rotation) {
            matrix.postRotate(180, centerX, centerY);
        }
        mTextureView.setTransform(matrix);//设置mTextureView的transformation
    }

...

 private void createCameraPreviewSession() {
        try {
            SurfaceTexture texture = mTextureView.getSurfaceTexture();//通过mTextureView获取SurfaceTexture。
            assert texture != null;

            // We configure the size of default buffer to be the size of camera preview we want.
            texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());//设置SurfaceTexture大小,预览尺寸

            // This is the output Surface we need to start preview.
            Surface surface = new Surface(texture);//通过SurfaceTexture创建Surface来预览。

            // We set up a CaptureRequest.Builder with the output Surface.
            mPreviewRequestBuilder
                    = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);//创建TEMPLATE_PREVIEW预览CaptureRequest.Builder
            mPreviewRequestBuilder.addTarget(surface);//CaptureRequest.Builder中添加Surface，即mTextureView获取创建的Surface

            // Here, we create a CameraCaptureSession for camera preview.
            mCameraDevice.createCaptureSession(Arrays.asList(surface, mImageReader.getSurface()),
                    new CameraCaptureSession.StateCallback() {//创建会话

                        @Override
                        public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {//创建会话成功
                            // The camera is already closed
                            if (null == mCameraDevice) {
                                return;
                            }

                            // When the session is ready, we start displaying the preview.
                            mCaptureSession = cameraCaptureSession;//从onConfigured参数获取mCaptureSession
                            try {
                                // Auto focus should be continuous for camera preview.
                                mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE,
                                        CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);//设置AF自动对焦模式
                                // Flash is automatically enabled when necessary.
                                setAutoFlash(mPreviewRequestBuilder);

                                // Finally, we start displaying the camera preview.
                                mPreviewRequest = mPreviewRequestBuilder.build();//转换为CaptureRequest
                                mCaptureSession.setRepeatingRequest(mPreviewRequest,
                                        mCaptureCallback, mBackgroundHandler);//设置预览,setRepeatingRequest不断的重复mPreviewRequest请求捕捉画面，常用于预览或者连拍场景。
                            } catch (CameraAccessException e) {
                                e.printStackTrace();
                            }
                        }

                        @Override
                        public void onConfigureFailed(//创建会话失败
                                                      @NonNull CameraCaptureSession cameraCaptureSession) {
                            showToast("Failed");
                        }
                    }, null
            );
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

...

 private CameraCaptureSession.CaptureCallback mCaptureCallback
            = new CameraCaptureSession.CaptureCallback() {//预览回调

        private void process(CaptureResult result) {
            switch (mState) {
                case STATE_PREVIEW: {//预览状态，则什么都不做
                    // We have nothing to do when the camera preview is working normally.
                    break;
                }
                case STATE_WAITING_LOCK: {//等待焦点被锁时，由设置拍照流时设置的STATE_WAITING_LOCK
                    Integer afState = result.get(CaptureResult.CONTROL_AF_STATE);
                    if (afState == null) {
                        captureStillPicture();//进行拍照
                    } else if (CaptureResult.CONTROL_AF_STATE_FOCUSED_LOCKED == afState ||
                            CaptureResult.CONTROL_AF_STATE_NOT_FOCUSED_LOCKED == afState) {
                        // CONTROL_AE_STATE can be null on some devices
                        Integer aeState = result.get(CaptureResult.CONTROL_AE_STATE);
                        if (aeState == null ||
                                aeState == CaptureResult.CONTROL_AE_STATE_CONVERGED) {
                            mState = STATE_PICTURE_TAKEN;
                            captureStillPicture();
                        } else {
                            runPrecaptureSequence();
                        }
                    }
                    break;
                }
                case STATE_WAITING_PRECAPTURE: {
                    // CONTROL_AE_STATE can be null on some devices
                    Integer aeState = result.get(CaptureResult.CONTROL_AE_STATE);
                    if (aeState == null ||
                            aeState == CaptureResult.CONTROL_AE_STATE_PRECAPTURE ||
                            aeState == CaptureRequest.CONTROL_AE_STATE_FLASH_REQUIRED) {
                        mState = STATE_WAITING_NON_PRECAPTURE;
                    }
                    break;
                }
                case STATE_WAITING_NON_PRECAPTURE: {
                    // CONTROL_AE_STATE can be null on some devices
                    Integer aeState = result.get(CaptureResult.CONTROL_AE_STATE);
                    if (aeState == null || aeState != CaptureResult.CONTROL_AE_STATE_PRECAPTURE) {
                        mState = STATE_PICTURE_TAKEN;
                        captureStillPicture();
                    }
                    break;
                }
            }
        }

...

 private void captureStillPicture() {//进行拍照
        try {
            final Activity activity = getActivity();
            if (null == activity || null == mCameraDevice) {
                return;
            }
            // This is the CaptureRequest.Builder that we use to take a picture.
            final CaptureRequest.Builder captureBuilder =
                    mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);//设置TEMPLATE_STILL_CAPTURE拍照CaptureRequest.Builder
            captureBuilder.addTarget(mImageReader.getSurface());//添加拍照mImageReader为Surface

            // Use the same AE and AF modes as the preview.//设置AF和AE
            captureBuilder.set(CaptureRequest.CONTROL_AF_MODE,
                    CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
            setAutoFlash(captureBuilder);

            // Orientation 设置成像方向
            int rotation = activity.getWindowManager().getDefaultDisplay().getRotation();
            captureBuilder.set(CaptureRequest.JPEG_ORIENTATION, getOrientation(rotation));//设置图片方向

            CameraCaptureSession.CaptureCallback CaptureCallback
                    = new CameraCaptureSession.CaptureCallback() {//拍照流程执行完成回调

                @Override
                public void onCaptureCompleted(@NonNull CameraCaptureSession session,
                                               @NonNull CaptureRequest request,
                                               @NonNull TotalCaptureResult result) {
                    showToast("Saved: " + mFile);//提示拍照图片已经保存
                    Log.d(TAG, mFile.toString());
                    unlockFocus();//释放焦点锁，重新开启预览。
                }
            };

            mCaptureSession.stopRepeating();//停止预览,停止任何一个正常进行的重复请求。
            mCaptureSession.abortCaptures();//中断Capture,尽可能快的取消当前队列中或正在处理中的所有捕捉请求。
            mCaptureSession.capture(captureBuilder.build(), CaptureCallback, null);//重新Capture进行拍照，这时mImageReader的回调会执行并保存图片
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }