title: How to do Android Motion Detection For Specific Area
body: <p>Trying to make a motion detection app based on <a href="https://github.com/jkwiecien/android-motion-detector" rel="nofollow noreferrer">this project</a>. The intention is to make the app take pictures when motion is detected by comparing two images. Up to this part, the app is working fine.</p>
  
  <p><strong>Requirement:</strong></p>
  
  <p>To specify area of detection by a custom view. So that, the pictures will be captured only if a motion is detected inside the defined area by calculating the detection area. </p>
  
  <p><strong>What I have done so far:</strong></p>
  
  <p>Created a movable custom view, like a crop view of which the dimensions (<code>Rect</code>) are saved in the preference each time when the view is moved.</p>
  
  <p><strong>What is not working:</strong>  </p>
  
  <p>The motion detection from inside the custom view is not working. I believe that the bitmaps must be cropped according to the size of the custom view to do the comparison. 
  In the detection thread I tried setting the <code>width</code> and <code>height</code> from the preference like : <code>
          private int width = Prefe.DetectionArea.width();
          private int height = Prefe.DetectionArea.height();</code> </p>
  
  <p>But it didn't work. Please help me by explaining how this could be achieved so that the motion detection will happen according to the size of the custom view. Any help is appreciated.</p>
  
  <p>Project Source Code: <a href="https://drive.google.com/drive/folders/0B7-oKqt7w49mbTR6VWZYVURmVms" rel="nofollow noreferrer">https://drive.google.com/drive/folders/0B7-oKqt7w49mbTR6VWZYVURmVms</a></p>
  
  <p><strong>MotionDetectionActivity.java</strong></p>
  
  <pre><code>public class MotionDetectionActivity extends SensorsActivity {
  
  private static final String TAG = "MotionDetectionActivity";
  private static long mReferenceTime = 0;
  private static IMotionDetection detector = null;
  public static MediaPlayer song;
  public static Vibrator mVibrator;
  
  private static SurfaceView preview = null;
  private static SurfaceHolder previewHolder = null;
  private static Camera camera = null;
  private static boolean inPreview = false;
  private static AreaDetectorView mDetector;
  private static FrameLayout layoutDetectorArea;
  static FrameLayout layoutMain;
  static View mView;
  private static volatile AtomicBoolean processing = new AtomicBoolean(false);
  
  /**
   * {@inheritDoc}
   */
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
      setContentView(R.layout.main);
  
      mVibrator = (Vibrator)this.getSystemService(VIBRATOR_SERVICE);
      layoutMain=(FrameLayout)findViewById(R.id.layoutMain);
      preview = (SurfaceView) findViewById(R.id.preview);
      previewHolder = preview.getHolder();
      previewHolder.addCallback(surfaceCallback);
      previewHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
      mView=layoutMain;
      mDetector= (AreaDetectorView) findViewById(R.id.viewDetector);
      layoutDetectorArea=(FrameLayout) findViewById(R.id.layoutDetectArea);
  
      ToggleButton toggle = (ToggleButton) findViewById(R.id.simpleToggleButton);
      toggle.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
          public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
              if (isChecked) {
                  // The toggle is enabled
  
  
              } else {
                  // The toggle is disabled
              }
          }
      });
  
  
      if (Preferences.USE_RGB) {
          detector = new RgbMotionDetection();
      } else if (Preferences.USE_LUMA) {
          detector = new LumaMotionDetection();
      } else {
          // Using State based (aggregate map)
          detector = new AggregateLumaMotionDetection();
      }
  }
  
  /**
   * {@inheritDoc}
   */
  @Override
  public void onConfigurationChanged(Configuration newConfig) {
      super.onConfigurationChanged(newConfig);
  }
  
  /**dd:
   * Song play # 1
   * Camera callback
   *
   * {@inheritDoc}
   */
  @Override
  public void onPause() {
      super.onPause();
      if(song!=null &amp;&amp; song.isPlaying())
      {
          song.stop();}
  
      camera.setPreviewCallback(null);
      if (inPreview) camera.stopPreview();
      inPreview = false;
      camera.release();
      camera = null;
  }
  
  /**
   * {@inheritDoc}
   */
  @Override
  public void onResume() {
      super.onResume();
  
      camera = Camera.open();
  }
  
  private PreviewCallback previewCallback = new PreviewCallback() {
  
      /**
       * {@inheritDoc}
       */
      @Override
      public void onPreviewFrame(byte[] data, Camera cam) {
          if (data == null) return;
          Camera.Size size = cam.getParameters().getPreviewSize();
          if (size == null) return;
  
          if (!GlobalData.isPhoneInMotion()) {
              DetectionThread thread = new DetectionThread(data, size.width, size.height);
              thread.start();
          }
      }
  };
  
  private SurfaceHolder.Callback surfaceCallback = new SurfaceHolder.Callback() {
  
      /**
       * {@inheritDoc}
       */
      @Override
      public void surfaceCreated(SurfaceHolder holder) {
          try {
  
              camera.setPreviewDisplay(previewHolder);
              camera.setPreviewCallback(previewCallback);
          } catch (Throwable t) {
              Log.e("Prek", "Exception in setPreviewDisplay()", t);
          }
      }
  
      /**
       * {@inheritDoc}
       */
      @Override
      public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
          if(camera != null) {
              Camera.Parameters parameters = camera.getParameters();
              parameters.setFocusMode(Camera.Parameters.FOCUS_MODE_CONTINUOUS_PICTURE);
              Camera.Size size = getBestPreviewSize(width, height, parameters);
              if (size != null) {
                  parameters.setPreviewSize(size.width, size.height);
                  Log.d(TAG, "Using width=" + size.width + " height=" + size.height);
              }
              camera.setParameters(parameters);
              camera.startPreview();
              inPreview = true;
          }
          //AreaDetectorView.InitDetectionArea();
      }
  
      /**
       * {@inheritDoc}
       */
      @Override
      public void surfaceDestroyed(SurfaceHolder holder) {
          // Ignore
      }
  };
  
  private static Camera.Size getBestPreviewSize(int width, int height, Camera.Parameters parameters) {
      Camera.Size result = null;
  
      for (Camera.Size size : parameters.getSupportedPreviewSizes()) {
          if (size.width &lt;= width &amp;&amp; size.height &lt;= height) {
              if (result == null) {
                  result = size;
              } else {
                  int resultArea = result.width * result.height;
                  int newArea = size.width * size.height;
  
                  if (newArea &gt; resultArea) result = size;
              }
          }
      }
  
      return result;
  }
  
  //***************Detection Class******************//
  
  private final class DetectionThread extends Thread {
  
      private byte[] data;
      private int width;
      private int height;
  
      public DetectionThread(byte[] data, int width, int height) {
          this.data = data;
          this.width = width;
          this.height = height;
      }
  
      /**
       * {@inheritDoc}
       */
      @Override
      public void run() {
          if (!processing.compareAndSet(false, true)) return;
  
          // Log.d(TAG, "BEGIN PROCESSING...");
          try {
              // Previous frame
              int[] pre = null;
              if (Preferences.SAVE_PREVIOUS) pre = detector.getPrevious();
  
              // Current frame (with changes)
              // long bConversion = System.currentTimeMillis();
              int[] img = null;
              if (Preferences.USE_RGB) {
                  img = ImageProcessing.decodeYUV420SPtoRGB(data, width, height);
              } else {
                  img = ImageProcessing.decodeYUV420SPtoLuma(data, width, height);
              }
  
  
              // Current frame (without changes)
              int[] org = null;
              if (Preferences.SAVE_ORIGINAL &amp;&amp; img != null) org = img.clone();
  
              if (img != null &amp;&amp; detector.detect(img, width, height)) {
  
  
                  // The delay is necessary to avoid taking a picture while in
                  // the
                  // middle of taking another. This problem can causes some
                  // phones
                  // to reboot.
                  long now = System.currentTimeMillis();
                  if (now &gt; (mReferenceTime + Preferences.PICTURE_DELAY)) {
                      mReferenceTime = now;
  
                      //mVibrator.vibrate(10);
  
                      Bitmap previous = null;
                      if (Preferences.SAVE_PREVIOUS &amp;&amp; pre != null) {
                          if (Preferences.USE_RGB) previous = ImageProcessing.rgbToBitmap(pre, width, height);
                          else previous = ImageProcessing.lumaToGreyscale(pre, width, height);
                      }
  
                      Bitmap original = null;
                      if (Preferences.SAVE_ORIGINAL &amp;&amp; org != null) {
                          if (Preferences.USE_RGB) original = ImageProcessing.rgbToBitmap(org, width, height);
                          else original = ImageProcessing.lumaToGreyscale(org, width, height);
                      }
  
                      Bitmap bitmap = null;
                      if (Preferences.SAVE_CHANGES) {
                          if (Preferences.USE_RGB) bitmap = ImageProcessing.rgbToBitmap(img, width, height);
                          else bitmap = ImageProcessing.lumaToGreyscale(img, width, height);
                      }
                      Log.i(TAG, "Saving.. previous=" + previous + " original=" + original + " bitmap=" + bitmap);
                      Looper.prepare();
                      new SavePhotoTask().execute(previous, original, bitmap);
                  } else {
                      Log.i(TAG, "Not taking picture because not enough time has passed since the creation of the Surface");
                  }
              }
          } catch (Exception e) {
              e.printStackTrace();
          } finally {
              processing.set(false);
          }
          // Log.d(TAG, "END PROCESSING...");
          processing.set(false);
      }
  };
  
  private static final class SavePhotoTask extends AsyncTask&lt;Bitmap, Integer, Integer&gt; {
  
      /**
       * {@inheritDoc}
       */
      @Override
      protected Integer doInBackground(Bitmap... data) {
          for (int i = 0; i &lt; data.length; i++) {
              Bitmap bitmap = data[i];
              String name = String.valueOf(System.currentTimeMillis());
              if (bitmap != null) save(name, bitmap);
          }
          return 1;
      }
  
      private void save(String name, Bitmap bitmap) {
          File photo = new File(Environment.getExternalStorageDirectory(), name + ".jpg");
          if (photo.exists()) photo.delete();
  
          try {
              FileOutputStream fos = new FileOutputStream(photo.getPath());
              bitmap.compress(Bitmap.CompressFormat.JPEG, 100, fos);
              fos.close();
          } catch (java.io.IOException e) {
              Log.e("PictureDemo", "Exception in photoCallback", e);
          }
      }
  }
  }
  </code></pre>
  
  <p><strong>AreaDetectorView.java</strong></p>
  
  <pre><code>public class  AreaDetectorView extends LinearLayout {
  
  public static int Width;
  public static int Height;
  
  private static Paint BoxPaint = null;
  private static Paint TextPaint = null;
  private static Paint ArrowPaint = null;
  private static Path mPath = null;
  private static Rect mRect = null;
  private static int lastX, lastY = 0;
  private static boolean mBoxTouched = false;
  private static boolean mArrowTouched = false;
  private static Context mContext;
  private static int ArrowWidth = 0;
  private static Paint BoxPaint2 = null;
  
  public AreaDetectorView(Context context) {
      super(context);
      mContext = context;
  }
  //attrs was not there
  public AreaDetectorView(Context context, AttributeSet attrs) {
      super(context,attrs);
      mContext = context;
      // TODO Auto-generated constructor stub
      if (!this.getRootView().isInEditMode()) {
          ArrowWidth =GetDisplayPixel(context, 30);
      }
  
      //InitDetectionArea();
  
      InitMemberVariables();
      setWillNotDraw(false);
  }
  public static int GetDisplayPixel(Context paramContext, int paramInt)
  {
      return (int)(paramInt * paramContext.getResources().getDisplayMetrics().density + 0.5F);
  }
  
  public static void InitMemberVariables() {
      if (BoxPaint == null) {
          BoxPaint = new Paint();
          BoxPaint.setAntiAlias(true);
          BoxPaint.setStrokeWidth(2.0f);
          //BoxPaint.setStyle(Style.STROKE);
          BoxPaint.setStyle(Style.FILL_AND_STROKE);
          BoxPaint.setColor(ContextCompat.getColor(mContext, R.color.bwff_60));
      }
      if (ArrowPaint == null) {
          ArrowPaint = new Paint();
          ArrowPaint.setAntiAlias(true);
          ArrowPaint.setColor(ContextCompat.getColor(mContext,R.color.redDD));
          ArrowPaint.setStyle(Style.FILL_AND_STROKE);
      }
      if (TextPaint == null) {
          TextPaint = new Paint();
          TextPaint.setColor(ContextCompat.getColor(mContext,R.color.yellowL));
          TextPaint.setTextSize(16);
          //txtPaint.setTypeface(lcd);
          TextPaint.setStyle(Style.FILL_AND_STROKE);
      }
      if (mPath == null) {
          mPath = new Path();
      } else {
          mPath.reset();
      }
      if (mRect == null) {
          mRect = new Rect();
      }
  
      if (BoxPaint2 == null) {
          BoxPaint2 = new Paint();
          BoxPaint2.setAntiAlias(true);
          BoxPaint2.setStrokeWidth(2.0f);
          //BoxPaint.setStyle(Style.STROKE);
          BoxPaint2.setStyle(Style.STROKE);
          BoxPaint2.setColor(ContextCompat.getColor(mContext,R.color.bwff_9e));
      }
  
  }
  
  public static void InitDetectionArea() {
      try {
          int w = Prefe.DetectionArea.width();
          int h = Prefe.DetectionArea.height();
          int x = Prefe.DetectionArea.left;
          int y = Prefe.DetectionArea.top;
  
          // ver 2.6.0
          if (Prefe.DetectionArea.left == 1
                  &amp;&amp; Prefe.DetectionArea.top == 1
                  &amp;&amp; Prefe.DetectionArea.right == 1
                  &amp;&amp; Prefe.DetectionArea.bottom == 1) {
  
              w = Prefe.DisplayWidth / 4;
              h = Prefe.DisplayHeight / 3;
  
              // ver 2.5.9
              w = Width / 4;
              h = Height / 3;
  
              Prefe.DetectorWidth = w;    //UtilGeneralHelper.GetDisplayPixel(this, 100);
              Prefe.DetectorHeight = h;   //UtilGeneralHelper.GetDisplayPixel(this, 100);
  
              x = (Prefe.DisplayWidth / 2) - (w / 2);
              y = (Prefe.DisplayHeight / 2) - (h / 2);
  
              // ver 2.5.9
              x = (Width / 2) - (w / 2);
              y = (Height / 2) - (h / 2);
  
          }
  
          //Prefe.DetectionArea = new Rect(x, x, x + Prefe.DetectorWidth, x + Prefe.DetectorHeight);
          Prefe.DetectionArea = new Rect(x, y, x + w, y + h);
  
          Prefe.gDetectionBitmapInt = new int[Prefe.DetectionArea.width() * Prefe.DetectionArea.height()];
          Prefe.gDetectionBitmapIntPrev = new int[Prefe.DetectionArea.width() * Prefe.DetectionArea.height()];
  
      } catch (Exception e) {
          e.printStackTrace();
      }
  }
  
  public static void SetDetectionArea(int x, int y, int w, int h) {
      try {
          Prefe.DetectionArea = new Rect(x, y, w, h);
  
      } catch (Exception e) {
          e.printStackTrace();
      }
  }
  
  private void DrawAreaBox(Canvas canvas) {
      try {
      } catch (Exception e) {
          e.printStackTrace();
      }
  }
  
  @Override
  protected void dispatchDraw(Canvas canvas) {
      try {
          if (this.getRootView().isInEditMode()) {
              super.dispatchDraw(canvas);
              return;
          }
  
          //canvas.save(Canvas.MATRIX_SAVE_FLAG);
          //Prefe.DetectionAreaOrient = UtilGeneralHelper.GetDetectRectByOrientation();
  
          canvas.drawColor(0);
          mPath.reset();
  
          canvas.drawRect(Prefe.DetectionArea, BoxPaint);
  
          mPath.moveTo(Prefe.DetectionArea.right - ArrowWidth, Prefe.DetectionArea.bottom);
          mPath.lineTo(Prefe.DetectionArea.right, Prefe.DetectionArea.bottom - ArrowWidth);
          mPath.lineTo(Prefe.DetectionArea.right, Prefe.DetectionArea.bottom);
          mPath.lineTo(Prefe.DetectionArea.right - ArrowWidth, Prefe.DetectionArea.bottom);
          mPath.close();
          canvas.drawPath(mPath, ArrowPaint);
  
          mPath.reset();
          //canvas.drawRect(Prefe.DetectionAreaOrient, BoxPaint2);
          //canvas.drawRect(Prefe.DetectionAreaOrientPort, BoxPaint2);
  
          TextPaint.setTextSize(16);
          //TextPaint.setLetterSpacing(2);
  
          TextPaint.setColor(ContextCompat.getColor(mContext,R.color.bwff));
  
          TextPaint.getTextBounds(getResources().getString(R.string.str_detectarea), 0, 1, mRect);
          canvas.drawText(getResources().getString(R.string.str_detectarea),
                  Prefe.DetectionArea.left + 4,
                  Prefe.DetectionArea.top + 4 + mRect.height(),
                  TextPaint);
          int recH = mRect.height();
  
          TextPaint.setStrokeWidth(1.2f);
          TextPaint.setTextSize(18);
          TextPaint.setColor(ContextCompat.getColor(mContext,R.color.redD_9e));
          TextPaint.getTextBounds(getResources().getString(R.string.str_dragandmove), 0, 1, mRect);
          canvas.drawText(getResources().getString(R.string.str_dragandmove),
                  Prefe.DetectionArea.left + 4,
                  Prefe.DetectionArea.top + 20 + mRect.height()*2,
                  TextPaint);
  
          TextPaint.getTextBounds(getResources().getString(R.string.str_scalearea), 0, 1, mRect);
          canvas.drawText(getResources().getString(R.string.str_scalearea),
                  Prefe.DetectionArea.left + 4,
                  Prefe.DetectionArea.top + 36 + mRect.height()*3,
                  TextPaint);
  
          super.dispatchDraw(canvas);
          //canvas.restore();
      } catch (Exception e) {
          e.printStackTrace();
      }
  }
  
  @Override
  protected void onDraw(Canvas canvas) {
      try {
          super.onDraw(canvas);
          invalidate();
      } catch (Exception e) {
          e.printStackTrace();
      } finally {
  
      }
  }
  
  @Override
  public boolean onTouchEvent(MotionEvent event) {
      boolean retValue = true;
      int X = (int)event.getX();
      int Y = (int)event.getY();
  
  
  
      //AppMain.txtLoc.setText(String.valueOf(X) + ", " + String.valueOf(Y));
  
      switch (event.getAction()) {
          case MotionEvent.ACTION_DOWN:
              mBoxTouched = TouchedInBoxArea(X, Y);
  
              //AppMain.txtLoc.setText("BoxTouched: " + String.valueOf(mBoxTouched));
  
              if (!mBoxTouched) break;
  
              lastX = X;
              lastY = Y;
  
              BoxPaint.setStyle(Style.FILL_AND_STROKE);
              BoxPaint.setColor(ContextCompat.getColor(mContext,R.color.redD_9e));
  
              mArrowTouched = TouchedInArrow(X, Y);
              //AppMain.txtLoc.setText("ArrowTouched: " + String.valueOf(mBoxTouched));
  
              if (mArrowTouched) {
                  ArrowPaint.setColor(ContextCompat.getColor(mContext,R.color.bwff_9e));
              }
  
              break;
  
          case MotionEvent.ACTION_MOVE:
              if (!mBoxTouched) break;
  
              int moveX = X - lastX;
              int moveY = Y - lastY;
  
              //AppMain.txtLoc.setText("Move X, Y: " + String.valueOf(moveX) + "," + String.valueOf(moveY));
              if (!mArrowTouched) {
                  if (Prefe.DetectionArea.left + moveX &lt; 0) {
                      break;
                  }
  //              if (Prefe.DetectionArea.right + moveX &gt; Prefe.gDisplay.getWidth()) {
  //                  break;
  //              }
                  // ver 2.5.9
                  if (Prefe.DetectionArea.right + moveX &gt; Width) {
                      break;
                  }
                  if (Prefe.DetectionArea.top + moveY &lt; 0) {
                      break;
                  }
  //              if (Prefe.DetectionArea.bottom + moveY &gt; Prefe.gDisplay.getHeight()) {
  //                  break;
  //              }
                  // ver 2.5.9
                  if (Prefe.DetectionArea.bottom + moveY &gt; Height) {
                      break;
                  }
              }
  
              if (mArrowTouched) {
                  if ((Prefe.DetectionArea.width() + moveX) &lt; ArrowWidth * 2){
                      break;
                  }
                  if ((Prefe.DetectionArea.height() + moveY) &lt; ArrowWidth * 2) {
                      break;
                  }
                  Prefe.DetectionArea.right += moveX;
                  Prefe.DetectionArea.bottom += moveY;
                  //Log.i("DBG", "W,H: " + String.valueOf(Prefe.DetectionArea.width()) + "," + String.valueOf(Prefe.DetectionArea.height()));
              } else {
                  Prefe.DetectionArea.left += moveX;
                  Prefe.DetectionArea.right += moveX;
                  Prefe.DetectionArea.top += moveY;
                  Prefe.DetectionArea.bottom += moveY;
              }
  
              lastX = X;
              lastY = Y;
  
              //AppMain.txtLoc.setText(String.valueOf(Prefe.DetectionArea.left) + ", " + String.valueOf(Prefe.DetectionArea.top));
              break;
  
          case MotionEvent.ACTION_UP:
              mBoxTouched = false;
              mArrowTouched = false;
              //BoxPaint.setStyle(Style.STROKE);
              BoxPaint.setStyle(Style.FILL_AND_STROKE);
              BoxPaint.setColor(ContextCompat.getColor(mContext,R.color.bwff_60));
              ArrowPaint.setColor(ContextCompat.getColor(mContext,R.color.redDD));
  
              //AppMain.txtLoc.setText(String.valueOf(Prefe.DetectionArea.left) + ", " + String.valueOf(Prefe.DetectionArea.top));
  
              if (Prefe.DetectionArea.left &lt; 0) {
                  Prefe.DetectionArea.left = 0;
              }
  //          if (Prefe.DetectionArea.right &gt; Prefe.gDisplay.getWidth()) {
  //              Prefe.DetectionArea.right = Prefe.gDisplay.getWidth();
  //          }
              // ver 2.5.9
              if (Prefe.DetectionArea.right &gt; Width) {
                  Prefe.DetectionArea.right = Width;
              }
              if (Prefe.DetectionArea.top &lt; 0) {
                  Prefe.DetectionArea.top = 0;
              }
  //          if (Prefe.DetectionArea.bottom &gt; Prefe.gDisplay.getHeight()) {
  //              Prefe.DetectionArea.bottom = Prefe.gDisplay.getHeight();
  //          }
              if (Prefe.DetectionArea.bottom &gt; Height) {
                  Prefe.DetectionArea.bottom = Height;
              }
  
              Prefe.gDetectionBitmapInt = new int[Prefe.DetectionArea.width() * Prefe.DetectionArea.height()];
              Prefe.gDetectionBitmapIntPrev = new int[Prefe.DetectionArea.width() * Prefe.DetectionArea.height()];
              //Prefe.gDetectionBitmapInt = null;
              //Prefe.gDetectionBitmapIntPrev = null;
  
              String area = String.valueOf(Prefe.DetectionArea.left)
                      + "," + String.valueOf(Prefe.DetectionArea.top)
                      + "," + String.valueOf(Prefe.DetectionArea.right)
                      + "," + String.valueOf(Prefe.DetectionArea.bottom);
  
             // UtilGeneralHelper.SavePreferenceSetting(Prefe.gContext, Prefe.PREF_DETECTION_AREA_KEY, area);
              //Saving the value
              SharedPrefsUtils.setStringPreference(mContext.getApplicationContext(), Prefe.PREF_DETECTION_AREA_KEY, area);
              Log.v("TAG", SharedPrefsUtils.getStringPreference(mContext.getApplicationContext(),Prefe.PREF_DETECTION_AREA_KEY));
  
  
              break;
      }
  
      invalidate();
      return retValue;
  }
  
  private boolean TouchedInBoxArea(int x, int y) {
      boolean retValue = false;
      try {
  
          if (x &gt; Prefe.DetectionArea.left &amp;&amp; x &lt; Prefe.DetectionArea.right) {
              if (y &gt; Prefe.DetectionArea.top &amp;&amp; y &lt; Prefe.DetectionArea.bottom) {
                  retValue = true;
              }
          }
      } catch (Exception e) {
          e.printStackTrace();
      }
      return retValue;
  }
  
  private boolean TouchedInArrow(int x, int y) {
      boolean retValue = false;
      try {
  
          if (x &gt; Prefe.DetectionArea.right - ArrowWidth &amp;&amp; x &lt; Prefe.DetectionArea.right) {
              if (y &gt; Prefe.DetectionArea.bottom - ArrowWidth &amp;&amp; y &lt; Prefe.DetectionArea.bottom) {
                  retValue = true;
              }
          }
      } catch (Exception e) {
          e.printStackTrace();
      }
      return retValue;
  }
  
  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
      super.onMeasure(widthMeasureSpec, heightMeasureSpec);
      int width = MeasureSpec.getSize(widthMeasureSpec);
      int height = MeasureSpec.getSize(heightMeasureSpec);
      setMeasuredDimension(width, height);
      Width = width;
      Height = height;
      InitDetectionArea();
  }
  
  @Override
  protected void onFinishInflate() {
      super.onFinishInflate();
  }
  
  @Override
  protected void onLayout(boolean changed, int l, int t, int r, int b) {
      // TODO Auto-generated method stub
      for (int i = 0; i &lt; this.getChildCount()-1; i++){
          (this.getChildAt(i)).layout(l, t, r, b);
      }
  
      if (changed) {
          // check width height
          if (r != Width || b != Height) {
              // size does not match
          }
      }
  }
  }
  </code></pre>
  
  <p><strong>Prefe.java</strong></p>
  
  <pre><code>public class Prefe extends Application{
  ...
  public static final String PREF_DETECTION_AREA_KEY = "pref_detection_area_key";
  }
  static{
  ...
  DetectionArea = new Rect(1, 1, 1, 1);
  }
  }
  </code></pre>