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。)

来源：http://blog.csdn.net/klxh2009/article/details/78326424