Android实现Camera2预览和拍照效果

简介

网上对于 Camera2 的介绍有很多，在 Github 上也有很多关于 Camera2 的封装库，但是对于那些库，封装性太强，有时候我们仅仅是需要个简简单单的拍照功能而已，因此，自定义一个 Camera 使之变得轻量级那是非常重要的了。(本文并非重复造轮子, 而是在于学习 Camera2API 的基本功能, 笔记之。)

学习要点:

使用 Android Camera2 API 的基本功能。
迭代连接到设备的所有相机的特征。
显示相机预览和拍摄照片。

Camera2 API 为连接到 Android 设备的各个相机设备提供了一个界面。 它替代了已弃用的 Camera 类。

• 使用 getCameraIdList 获取所有可用摄像机的列表。 然后，您可以使用 getCameraCharacteristics，并找到适合您需要的最佳相机（前 / 后面，分辨率等）。
• 创建一个 CameraDevice.StateCallback 的实例并打开相机。 当相机打开时，准备开始相机预览。
• 使用 TextureView 显示相机预览。 创建一个 CameraCaptureSession 并设置一个重复的 CaptureRequest。
• 静像拍摄需要几个步骤。 首先，需要通过更新相机预览的 CaptureRequest 来锁定相机的焦点。
• 然后，以类似的方式，需要运行一个预捕获序列。之后，它准备拍摄一张照片。 创建一个新的 CaptureRequest 并调用 [capture] 。

完成后，别忘了解锁焦点。

实现效果

环境

SDK>21

Camera2 类图

代码实现

CameraPreview.java

/**
 * Created by shenhua on 2017-10-20-0020.
 * Email shenhuanet@126.com
 */
public class CameraPreview extends TextureView {

  private static final String TAG = "CameraPreview";
  private static final SparseIntArray ORIENTATIONS = new SparseIntArray();//从屏幕旋转转换为JPEG方向
  private static final int MAX_PREVIEW_WIDTH = 1920;//Camera2 API 保证的最大预览宽高
  private static final int MAX_PREVIEW_HEIGHT = 1080;
  private static final int STATE_PREVIEW = 0;//显示相机预览
  private static final int STATE_WAITING_LOCK = 1;//焦点锁定中
  private static final int STATE_WAITING_PRE_CAPTURE = 2;//拍照中
  private static final int STATE_WAITING_NON_PRE_CAPTURE = 3;//其它状态
  private static final int STATE_PICTURE_TAKEN = 4;//拍照完毕
  private int mState = STATE_PREVIEW;
  private int mRatioWidth = 0, mRatioHeight = 0;
  private int mSensorOrientation;
  private boolean mFlashSupported;

  private Semaphore mCameraOpenCloseLock = new Semaphore(1);//使用信号量 Semaphore 进行多线程任务调度
  private Activity activity;
  private File mFile;
  private HandlerThread mBackgroundThread;
  private Handler mBackgroundHandler;
  private Size mPreviewSize;
  private String mCameraId;
  private CameraDevice mCameraDevice;
  private CaptureRequest.Builder mPreviewRequestBuilder;
  private CaptureRequest mPreviewRequest;
  private CameraCaptureSession mCaptureSession;
  private ImageReader mImageReader;

  static {
    ORIENTATIONS.append(Surface.ROTATION_0, 90);
    ORIENTATIONS.append(Surface.ROTATION_90, 0);
    ORIENTATIONS.append(Surface.ROTATION_180, 270);
    ORIENTATIONS.append(Surface.ROTATION_270, 180);
  }

  public CameraPreview(Context context) {
    this(context, null);
  }

  public CameraPreview(Context context, AttributeSet attrs) {
    this(context, attrs, 0);
  }

  public CameraPreview(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    mFile = new File(getContext().getExternalFilesDir(null), "pic.jpg");
  }

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    int width = MeasureSpec.getSize(widthMeasureSpec);
    int height = MeasureSpec.getSize(heightMeasureSpec);
    if (0 == mRatioWidth || 0 == mRatioHeight) {
      setMeasuredDimension(width, height);
    } else {
      if (width < height * mRatioWidth / mRatioHeight) {
        setMeasuredDimension(width, width * mRatioHeight / mRatioWidth);
      } else {
        setMeasuredDimension(height * mRatioWidth / mRatioHeight, height);
      }
    }
  }

  public void onResume(Activity activity) {
    this.activity = activity;
    startBackgroundThread();
    //当Activity或Fragment OnResume()时,可以冲洗打开一个相机并开始预览,否则,这个Surface已经准备就绪
    if (this.isAvailable()) {
      openCamera(this.getWidth(), this.getHeight());
    } else {
      this.setSurfaceTextureListener(mSurfaceTextureListener);
    }
  }

  public void onPause() {
    closeCamera();
    stopBackgroundThread();
  }

  public void setOutPutDir(File file) {
    this.mFile = file;
  }

  public void setAspectRatio(int width, int height) {
    if (width < 0 || height < 0) {
      throw new IllegalArgumentException("Size can't be negative");
    }
    mRatioWidth = width;
    mRatioHeight = height;
    requestLayout();
  }

  public void setAutoFlash(CaptureRequest.Builder requestBuilder) {
    if (mFlashSupported) {
      requestBuilder.set(CaptureRequest.CONTROL_AE_MODE,
          CaptureRequest.CONTROL_AE_MODE_ON_AUTO_FLASH);
    }
  }

  public void takePicture() {
    lockFocus();
  }

  private void startBackgroundThread() {
    mBackgroundThread = new HandlerThread("CameraBackground");
    mBackgroundThread.start();
    mBackgroundHandler = new Handler(mBackgroundThread.getLooper());
  }

  private void stopBackgroundThread() {
    mBackgroundThread.quitSafely();
    try {
      mBackgroundThread.join();
      mBackgroundThread = null;
      mBackgroundHandler = null;
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }

  /**
   * 处理生命周期内的回调事件
   */
  private final TextureView.SurfaceTextureListener mSurfaceTextureListener = new TextureView.SurfaceTextureListener() {

    @Override
    public void onSurfaceTextureAvailable(SurfaceTexture texture, int width, int height) {
      openCamera(width, height);
    }

    @Override
    public void onSurfaceTextureSizeChanged(SurfaceTexture texture, int width, int height) {
      configureTransform(width, height);
    }

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

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

  /**
   * 相机状态改变回调
   */
  private final CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() {

    @Override
    public void onOpened(@NonNull CameraDevice cameraDevice) {
      mCameraOpenCloseLock.release();
      Log.d(TAG, "相机已打开");
      mCameraDevice = cameraDevice;
      createCameraPreviewSession();
    }

    @Override
    public void onDisconnected(@NonNull CameraDevice cameraDevice) {
      mCameraOpenCloseLock.release();
      cameraDevice.close();
      mCameraDevice = null;
    }

    @Override
    public void onError(@NonNull CameraDevice cameraDevice, int error) {
      mCameraOpenCloseLock.release();
      cameraDevice.close();
      mCameraDevice = null;
      if (null != activity) {
        activity.finish();
      }
    }
  };

  /**
   * 处理与照片捕获相关的事件
   */
  private CameraCaptureSession.CaptureCallback mCaptureCallback = new CameraCaptureSession.CaptureCallback() {

    private void process(CaptureResult result) {
      switch (mState) {
        case STATE_PREVIEW: {
          break;
        }
        case STATE_WAITING_LOCK: {
          Integer afState = result.get(CaptureResult.CONTROL_AF_STATE);
          if (afState == null) {
            captureStillPicture();
          } else if (CaptureResult.CONTROL_AF_STATE_FOCUSED_LOCKED == afState ||
              CaptureResult.CONTROL_AF_STATE_NOT_FOCUSED_LOCKED == afState) {
            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_PRE_CAPTURE: {
          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_PRE_CAPTURE;
          }
          break;
        }
        case STATE_WAITING_NON_PRE_CAPTURE: {
          Integer aeState = result.get(CaptureResult.CONTROL_AE_STATE);
          if (aeState == null || aeState != CaptureResult.CONTROL_AE_STATE_PRECAPTURE) {
            mState = STATE_PICTURE_TAKEN;
            captureStillPicture();
          }
          break;
        }
      }
    }

    @Override
    public void onCaptureProgressed(@NonNull CameraCaptureSession session,
                    @NonNull CaptureRequest request,
                    @NonNull CaptureResult partialResult) {
      process(partialResult);
    }

    @Override
    public void onCaptureCompleted(@NonNull CameraCaptureSession session,
                    @NonNull CaptureRequest request,
                    @NonNull TotalCaptureResult result) {
      process(result);
    }

  };

  /**
   * 在确定相机预览大小后应调用此方法
   *
   * @param viewWidth 宽
   * @param viewHeight 高
   */
  private void configureTransform(int viewWidth, int viewHeight) {
    if (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);
    }
    this.setTransform(matrix);
  }

  /**
   * 根据mCameraId打开相机
   */
  private void openCamera(int width, int height) {
    setUpCameraOutputs(width, height);
    configureTransform(width, height);
    CameraManager manager = (CameraManager) getContext().getSystemService(Context.CAMERA_SERVICE);
    try {
      if (!mCameraOpenCloseLock.tryAcquire(2500, TimeUnit.MILLISECONDS)) {
        throw new RuntimeException("Time out waiting to lock camera opening.");
      }
      if (ActivityCompat.checkSelfPermission(activity, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
        // TODO: Consider calling
        //  ActivityCompat#requestPermissions
        // here to request the missing permissions, and then overriding
        //  public void onRequestPermissionsResult(int requestCode, String[] permissions,
        //                     int[] grantResults)
        // to handle the case where the user grants the permission. See the documentation
        // for ActivityCompat#requestPermissions for more details.
        return;
      }
      manager.openCamera(mCameraId, mStateCallback, mBackgroundHandler);
    } catch (CameraAccessException e) {
      e.printStackTrace();
    } catch (InterruptedException e) {
      throw new RuntimeException("Interrupted while trying to lock camera opening.", e);
    }
  }

  /**
   * 关闭相机
   */
  private void closeCamera() {
    try {
      mCameraOpenCloseLock.acquire();
      if (null != mCaptureSession) {
        mCaptureSession.close();
        mCaptureSession = null;
      }
      if (null != mCameraDevice) {
        mCameraDevice.close();
        mCameraDevice = null;
      }
      if (null != mImageReader) {
        mImageReader.close();
        mImageReader = null;
      }
    } catch (InterruptedException e) {
      throw new RuntimeException("Interrupted while trying to lock camera closing.", e);
    } finally {
      mCameraOpenCloseLock.release();
    }
  }

  /**
   * 设置相机相关的属性或变量
   *
   * @param width 相机预览的可用尺寸的宽度
   * @param height 相机预览的可用尺寸的高度
   */
  @SuppressWarnings("SuspiciousNameCombination")
  private void setUpCameraOutputs(int width, int height) {
    CameraManager manager = (CameraManager) getContext().getSystemService(Context.CAMERA_SERVICE);
    try {
      for (String cameraId : manager.getCameraIdList()) {
        CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
        // 在这个例子中不使用前置摄像头
        Integer facing = characteristics.get(CameraCharacteristics.LENS_FACING);
        if (facing != null && facing == CameraCharacteristics.LENS_FACING_FRONT) {
          continue;
        }
        StreamConfigurationMap map = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
        if (map == null) {
          continue;
        }

        Size largest = Collections.max(Arrays.asList(map.getOutputSizes(ImageFormat.JPEG)),
            new CompareSizesByArea());
        mImageReader = ImageReader.newInstance(largest.getWidth(), largest.getHeight(),
            ImageFormat.JPEG, /*maxImages*/2);
        mImageReader.setOnImageAvailableListener(
            mOnImageAvailableListener, mBackgroundHandler);

        int displayRotation = activity.getWindowManager().getDefaultDisplay().getRotation();
        // noinspection ConstantConditions
        mSensorOrientation = characteristics.get(CameraCharacteristics.SENSOR_ORIENTATION);
        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) {
          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;
        }

        mPreviewSize = chooseOptimalSize(map.getOutputSizes(SurfaceTexture.class),
            rotatedPreviewWidth, rotatedPreviewHeight, maxPreviewWidth,
            maxPreviewHeight, largest);

        int orientation = getResources().getConfiguration().orientation;
        if (orientation == Configuration.ORIENTATION_LANDSCAPE) {
          setAspectRatio(mPreviewSize.getWidth(), mPreviewSize.getHeight());
        } else {
          setAspectRatio(mPreviewSize.getHeight(), mPreviewSize.getWidth());
        }
        Boolean available = characteristics.get(CameraCharacteristics.FLASH_INFO_AVAILABLE);
        mFlashSupported = available == null ? false : available;

        mCameraId = cameraId;
        return;
      }
    } catch (CameraAccessException e) {
      e.printStackTrace();
    } catch (NullPointerException e) {
      Log.e(TAG, "设备不支持Camera2");
    }
  }

  /**
   * 获取一个合适的相机预览尺寸
   *
   * @param choices      支持的预览尺寸列表
   * @param textureViewWidth 相对宽度
   * @param textureViewHeight 相对高度
   * @param maxWidth     可以选择的最大宽度
   * @param maxHeight     可以选择的最大高度
   * @param aspectRatio    宽高比
   * @return 最佳预览尺寸
   */
  private static Size chooseOptimalSize(Size[] choices, int textureViewWidth, int textureViewHeight,
                     int maxWidth, int maxHeight, Size aspectRatio) {
    List<Size> bigEnough = new ArrayList<>();
    List<Size> notBigEnough = new ArrayList<>();
    int w = aspectRatio.getWidth();
    int h = aspectRatio.getHeight();
    for (Size option : choices) {
      if (option.getWidth() <= maxWidth && option.getHeight() <= maxHeight &&
          option.getHeight() == option.getWidth() * h / w) {
        if (option.getWidth() >= textureViewWidth &&
            option.getHeight() >= textureViewHeight) {
          bigEnough.add(option);
        } else {
          notBigEnough.add(option);
        }
      }
    }
    if (bigEnough.size() > 0) {
      return Collections.min(bigEnough, new CompareSizesByArea());
    } else if (notBigEnough.size() > 0) {
      return Collections.max(notBigEnough, new CompareSizesByArea());
    } else {
      Log.e(TAG, "Couldn't find any suitable preview size");
      return choices[0];
    }
  }

  /**
   * 为相机预览创建新的CameraCaptureSession
   */
  private void createCameraPreviewSession() {
    try {
      SurfaceTexture texture = this.getSurfaceTexture();
      assert texture != null;
      // 将默认缓冲区的大小配置为想要的相机预览的大小
      texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
      Surface surface = new Surface(texture);
      mPreviewRequestBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
      mPreviewRequestBuilder.addTarget(surface);
      // 我们创建一个 CameraCaptureSession 来进行相机预览
      mCameraDevice.createCaptureSession(Arrays.asList(surface, mImageReader.getSurface()),
          new CameraCaptureSession.StateCallback() {

            @Override
            public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
              if (null == mCameraDevice) {
                return;
              }
              // 会话准备好后，我们开始显示预览
              mCaptureSession = cameraCaptureSession;
              try {
                mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE,
                    CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
                setAutoFlash(mPreviewRequestBuilder);
                mPreviewRequest = mPreviewRequestBuilder.build();
                mCaptureSession.setRepeatingRequest(mPreviewRequest, mCaptureCallback, mBackgroundHandler);
              } catch (CameraAccessException e) {
                e.printStackTrace();
              }
            }

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

  /**
   * 从指定的屏幕旋转中检索照片方向
   *
   * @param rotation 屏幕方向
   * @return 照片方向（0,90,270,360）
   */
  private int getOrientation(int rotation) {
    return (ORIENTATIONS.get(rotation) + mSensorOrientation + 270) % 360;
  }

  /**
   * 锁定焦点
   */
  private void lockFocus() {
    try {
      // 如何通知相机锁定焦点
      mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_TRIGGER, CameraMetadata.CONTROL_AF_TRIGGER_START);
      // 通知mCaptureCallback等待锁定
      mState = STATE_WAITING_LOCK;
      mCaptureSession.capture(mPreviewRequestBuilder.build(), mCaptureCallback, mBackgroundHandler);
    } catch (CameraAccessException e) {
      e.printStackTrace();
    }
  }

  /**
   * 解锁焦点
   */
  private void unlockFocus() {
    try {
      mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_TRIGGER,
          CameraMetadata.CONTROL_AF_TRIGGER_CANCEL);
      setAutoFlash(mPreviewRequestBuilder);
      mCaptureSession.capture(mPreviewRequestBuilder.build(), mCaptureCallback,
          mBackgroundHandler);
      mState = STATE_PREVIEW;
      mCaptureSession.setRepeatingRequest(mPreviewRequest, mCaptureCallback,
          mBackgroundHandler);
    } catch (CameraAccessException e) {
      e.printStackTrace();
    }
  }

  /**
   * 拍摄静态图片
   */
  private void captureStillPicture() {
    try {
      if (null == activity || null == mCameraDevice) {
        return;
      }
      final CaptureRequest.Builder captureBuilder =
          mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
      captureBuilder.addTarget(mImageReader.getSurface());
      captureBuilder.set(CaptureRequest.CONTROL_AF_MODE,
          CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
      setAutoFlash(captureBuilder);
      // 方向
      int rotation = activity.getWindowManager().getDefaultDisplay().getRotation();
      captureBuilder.set(CaptureRequest.JPEG_ORIENTATION, getOrientation(rotation));
      CameraCaptureSession.CaptureCallback captureCallback
          = new CameraCaptureSession.CaptureCallback() {

        @Override
        public void onCaptureCompleted(@NonNull CameraCaptureSession session,
                        @NonNull CaptureRequest request,
                        @NonNull TotalCaptureResult result) {
          Toast.makeText(getContext(), "Saved: " + mFile, Toast.LENGTH_SHORT).show();
          Log.d(TAG, mFile.toString());
          unlockFocus();
        }
      };
      mCaptureSession.stopRepeating();
      mCaptureSession.abortCaptures();
      mCaptureSession.capture(captureBuilder.build(), captureCallback, null);
    } catch (CameraAccessException e) {
      e.printStackTrace();
    }
  }

  /**
   * 运行preCapture序列来捕获静止图像
   */
  private void runPreCaptureSequence() {
    try {
      // 设置拍照参数请求
      mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER,
          CaptureRequest.CONTROL_AE_PRECAPTURE_TRIGGER_START);
      mState = STATE_WAITING_PRE_CAPTURE;
      mCaptureSession.capture(mPreviewRequestBuilder.build(), mCaptureCallback, mBackgroundHandler);
    } catch (CameraAccessException e) {
      e.printStackTrace();
    }
  }

  /**
   * 比较两者大小
   */
  private static class CompareSizesByArea implements Comparator<Size> {

    @Override
    public int compare(Size lhs, Size rhs) {
      return Long.signum((long) lhs.getWidth() * lhs.getHeight() -
          (long) rhs.getWidth() * rhs.getHeight());
    }
  }

  /**
   * ImageReader的回调对象
   */
  private final ImageReader.OnImageAvailableListener mOnImageAvailableListener
      = new ImageReader.OnImageAvailableListener() {

    @Override
    public void onImageAvailable(ImageReader reader) {
      mBackgroundHandler.post(new ImageSaver(reader.acquireNextImage(), mFile));
    }
  };

  /**
   * 将捕获到的图像保存到指定的文件中
   */
  private static class ImageSaver implements Runnable {

    private final Image mImage;
    private final File mFile;

    ImageSaver(Image image, File file) {
      mImage = image;
      mFile = file;
    }

    @Override
    public void run() {
      ByteBuffer buffer = mImage.getPlanes()[0].getBuffer();
      byte[] bytes = new byte[buffer.remaining()];
      buffer.get(bytes);
      FileOutputStream output = null;
      try {
        output = new FileOutputStream(mFile);
        output.write(bytes);
      } catch (IOException e) {
        e.printStackTrace();
      } finally {
        mImage.close();
        if (null != output) {
          try {
            output.close();
          } catch (IOException e) {
            e.printStackTrace();
          }
        }
      }
    }
  }

}

MainActivity.java

public class MainActivity extends AppCompatActivity {

  CameraPreview cameraView;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    cameraView = (CameraPreview) findViewById(R.id.cameraView);
  }

  @Override
  protected void onResume() {
    super.onResume();
    cameraView.onResume(this);
  }

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

  public void takePic(View view) {
    cameraView.takePicture();
  }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  xmlns:tools="http://schemas.android.com/tools"
  android:id="@+id/constraintLayout"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:background="@android:color/black"
  tools:context="com.shenhua.ocr.activity.Main2Activity">

  <com.shenhua.ocr.widget.CameraPreview
    android:id="@+id/cameraView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

  <Button
    android:layout_width="70dp"
    android:layout_height="70dp"
    android:layout_gravity="center"
    android:background="@drawable/ic_capture_200px"
    android:onClick="takePic"
    android:text="TAKE"
    app:layout_constraintBottom_toBottomOf="@id/constraintLayout"
    app:layout_constraintEnd_toEndOf="@id/constraintLayout"
    app:layout_constraintStart_toStartOf="@id/constraintLayout"
    app:layout_constraintTop_toTopOf="@id/cameraView"
    app:layout_constraintVertical_bias="0.97" />

</android.support.constraint.ConstraintLayout>

资源文件 ic_capture_200px.xml

<vector android:height="24dp" android:viewportHeight="1024.0"
  android:viewportWidth="1024.0" android:width="24dp" xmlns:android="http://schemas.android.com/apk/res/android">
  <path android:fillColor="#03A9F4" android:pathData="M512,512m-393.8,0a393.8,393.8 0,1 0,787.7 0,393.8 393.8,0 1,0 -787.7,0Z"/>
  <path android:fillColor="#03A9F4" android:pathData="M512,1024C229.2,1024 0,794.8 0,512S229.2,0 512,0s512,229.2 512,512 -229.2,512 -512,512zM512,984.6c261,0 472.6,-211.6 472.6,-472.6S773,39.4 512,39.4 39.4,251 39.4,512s211.6,472.6 472.6,472.6z"/>
</vector>

其它

Manifest 权限:

<uses-permission android:name="android.permission.CAMERA" />
<uses-feature android:name="android.hardware.camera" />
<uses-feature android:name="android.hardware.camera.autofocus" />

Android6.0 运行时权限未贴出。(注意：为了方便读者手机端阅读，本文代码部分的成员变量使用了行尾注释，在正常编程习惯中，请使用 /* / 注释。)

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