上一篇博文简单介绍了使用Camera2 API拍摄照片，并使用SurfaceView作为预览界面。实际上，相对于SurfaceView, TextureView更适合用于视频和拍摄照片。SurfaceView也有它的使用场合，这将在另外一篇中阐述。本文将使用TextureView作为预览界面，再次向大家展示Camera2 API的简单应用。

1，定义TextureView作为预览界面

在布局文件中加入TextureView控件，然后实现其监听事件

textureView = (TextureView) findViewById(R.id.textureView);
然后我们可以在OnResume()方法中设置监听SurefaceTexture的事件

textureView.setSurfaceTextureListener(textureListener);

当SurefaceTexture准备好后会回调SurfaceTextureListener 的onSurfaceTextureAvailable()方法

private TextureView.SurfaceTextureListener mTextureListener = new TextureView.SurfaceTextureListener() {
        @Override
        public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {
            //当SurefaceTexture可用的时候，设置相机参数并打开相机
            setupCamera(width, 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) {

        }
    };

2，设置相机参数

private void setupCamera(int width, int height) {
        //获取摄像头的管理者CameraManager
        CameraManager manager = (CameraManager) getContext().getSystemService(Context.CAMERA_SERVICE);
        try {
            //遍历所有摄像头
            for (String cameraId : manager.getCameraIdList()) {
                CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
                Integer facing = characteristics.get(CameraCharacteristics.LENS_FACING);
                //此处默认打开后置摄像头
                if (facing != null && facing == CameraCharacteristics.LENS_FACING_FRONT)
                    continue;
                //获取StreamConfigurationMap，它是管理摄像头支持的所有输出格式和尺寸
                StreamConfigurationMap map = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
                assert map != null;
                //根据TextureView的尺寸设置预览尺寸
                mPreviewSize = getOptimalSize(map.getOutputSizes(SurfaceTexture.class), width, height);
                //获取相机支持的最大拍照尺寸
                mCaptureSize = Collections.max(Arrays.asList(map.getOutputSizes(ImageFormat.JPEG)), new Comparator<Size>() {
                    @Override
                    public int compare(Size lhs, Size rhs) {
                        return Long.signum(lhs.getWidth() * lhs.getHeight() - rhs.getHeight() * rhs.getWidth());
                    }
                });
                //此ImageReader用于拍照所需
                setupImageReader();
                mCameraId = cameraId;
                break;
            }
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

//选择sizeMap中大于并且最接近width和height的size
    private Size getOptimalSize(Size[] sizeMap, int width, int height) {
        List<Size> sizeList = new ArrayList<>();
        for (Size option : sizeMap) {
            if (width > height) {
                if (option.getWidth() > width && option.getHeight() > height) {
                    sizeList.add(option);
                }
            } else {
                if (option.getWidth() > height && option.getHeight() > width) {
                    sizeList.add(option);
                }
            }
        }
        if (sizeList.size() > 0) {
            return Collections.min(sizeList, new Comparator<Size>() {
                @Override
                public int compare(Size lhs, Size rhs) {
                    return Long.signum(lhs.getWidth() * lhs.getHeight() - rhs.getWidth() * rhs.getHeight());
                }
            });
        }
        return sizeMap[0];
    }

private void setupImageReader() {
        //2代表ImageReader中最多可以获取两帧图像流
        mImageReader = ImageReader.newInstance(mCaptureSize.getWidth(), mCaptureSize.getHeight(),
                ImageFormat.JPEG, 1);
        mImageReader.setOnImageAvailableListener(new ImageReader.OnImageAvailableListener() {
            @Override
            public void onImageAvailable(ImageReader reader) {
                final Image image = reader.acquireNextImage();
                mCameraHandler.post(new imageSaver(image));
                getActivity().runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        ByteBuffer buffer = image.getPlanes()[0].getBuffer();
                        byte[] bytes = new byte[buffer.remaining()];
                        buffer.get(bytes);//由缓冲区存入字节数组
                        final Bitmap bitmap = BitmapFactory.decodeByteArray(bytes, 0, bytes.length);
                        if (bitmap != null) {
                            ivShow.setImageBitmap(bitmap);
                        }
                    }
                });
            }
        }, mCameraHandler);
    }

public static class imageSaver implements Runnable {

        private Image mImage;

        public imageSaver(Image image) {
            mImage = image;
        }

        @Override
        public void run() {
            ByteBuffer buffer = mImage.getPlanes()[0].getBuffer();
            byte[] data = new byte[buffer.capacity()];
            buffer.get(data);
            String path = Environment.getExternalStorageDirectory() + "/DCIM/361camera/";
            File mImageFile = new File(path);
            if (!mImageFile.exists()) {
                boolean ret = mImageFile.mkdirs();
                assert (ret);
            }
            String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
            String fileName = path + "IMG_" + timeStamp + ".jpg";
            FileOutputStream fos = null;
            try {
                fos = new FileOutputStream(fileName);
                fos.write(data, 0, data.length);
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                if (fos != null) {
                    try {
                        fos.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                mImage.close();
            }
        }
    }

3，开启相机

private void openCamera() {
        mCameraManager = (CameraManager) getContext().getSystemService(Context.CAMERA_SERVICE);
        try {
            if (ActivityCompat.checkSelfPermission(getContext(), Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                //申请WRITE_EXTERNAL_STORAGE权限
                requestPermissions(new String[]{Manifest.permission.CAMERA},
                        REQUEST_CAMERA_CODE);
                //return;
            } else {
                mCameraManager.openCamera(mCameraId, mStateCallback, mCameraHandler);
            }
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

private CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() {
        @Override
        public void onOpened(CameraDevice camera) {
            mCameraDevice = camera;
            startPreview();
        }

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

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

4，开启相机预览

private void startPreview() {
        SurfaceTexture mSurfaceTexture = mTextureView.getSurfaceTexture();
        mSurfaceTexture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
        Surface previewSurface = new Surface(mSurfaceTexture);
        try {
            mCaptureRequestBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
            mCaptureRequestBuilder.addTarget(previewSurface);
            mCameraDevice.createCaptureSession(Arrays.asList(previewSurface, mImageReader.getSurface()), new CameraCaptureSession.StateCallback() {
                @Override
                public void onConfigured(CameraCaptureSession session) {
                    try {
                        mCaptureRequest = mCaptureRequestBuilder.build();
                        mCameraCaptureSession = session;
                        mCameraCaptureSession.setRepeatingRequest(mCaptureRequest, null, mCameraHandler);
                    } catch (CameraAccessException e) {
                        e.printStackTrace();
                    }
                }

                @Override
                public void onConfigureFailed(CameraCaptureSession session) {

                }
            }, mCameraHandler);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

5，实现PreviewCallback

首先创建一个ImageReader，并监听它的事件（见上面的代码setupImageReader()）。然后开启预览之前，设置ImageReader为输出Surface（见上面setupCamera()的代码）。

6，拍照

public void takePicture() {
        lockFocus();
    }

    private void lockFocus() {
        try {
            mCaptureRequestBuilder.set(CaptureRequest.CONTROL_AF_TRIGGER, CameraMetadata.CONTROL_AF_TRIGGER_START);
            mCameraCaptureSession.capture(mCaptureRequestBuilder.build(), mCaptureCallback, mCameraHandler);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }