code: @Override
      @NonNull
      public Rect evaluate(float fraction, @NonNull Rect startValue, @NonNull Rect endValue) {
          int left = startValue.left + (int) ((endValue.left - startValue.left) * fraction);
          int top = startValue.top + (int) ((endValue.top - startValue.top) * fraction);
          int right = startValue.right + (int) ((endValue.right - startValue.right) * fraction);
          int bottom = startValue.bottom + (int) ((endValue.bottom - startValue.bottom) * fraction);
          if (mRect == null) {
              return new Rect(left, top, right, bottom);
          } else {
              mRect.set(left, top, right, bottom);
              return mRect;
          }
      }
docs: This function returns the result of linearly interpolating the start and
  end Rect values, with <code>fraction</code> representing the proportion
  between the start and end values. The calculation is a simple parametric
  calculation on each of the separate components in the Rect objects
  (left, top, right, and bottom).
  
  <p>If {@link #RectEvaluator(android.graphics.Rect)} was used to construct
  this RectEvaluator, the object returned will be the <code>reuseRect</code>
  passed into the constructor.</p>
  
  @param fraction   The fraction from the starting to the ending values
  @param startValue The start Rect
  @param endValue   The end Rect
  @return A linear interpolation between the start and end values, given the
  <code>fraction</code> parameter.