code: public CalendarDay getDayFromLocation(float x, float y) {
          int dayStart = mPadding;
          if (x < dayStart || x > mWidth - mPadding) {
              return null;
          }
          // Selection is (x - start) / (pixels/day) == (x -s) * day / pixels
          int row = (int) (y - MONTH_HEADER_SIZE) / mRowHeight;
          int column = (int) ((x - dayStart) * mNumDays / (mWidth - dayStart - mPadding));
  
          int day = column - findDayOffset() + 1;
          day += row * mNumDays;
          if (day < 1 || day > mNumCells) {
              return null;
          }
          return new CalendarDay(mYear, mMonth, day);
      }
docs: Calculates the day that the given x position is in, accounting for week
  number. Returns a Time referencing that day or null if
  
  @param x The x position of the touch event
  @return A time object for the tapped day or null if the position wasn't
  in a day