@Override void updateTextPositions(int position, float positionOffset, boolean force) {
    final Rect r = mTempRect;
    int bottom = getHeight();
    int left = mCurrText.getLeft() - mTabPadding;
    int right = mCurrText.getRight() + mTabPadding;
    int top = bottom - mIndicatorHeight;

    r.set(left, top, right, bottom);

    super.updateTextPositions(position, positionOffset, force);
    mTabAlpha = (int) (Math.abs(positionOffset - 0.5f) * 2 * 0xFF);

    left = mCurrText.getLeft() - mTabPadding;
    right = mCurrText.getRight() + mTabPadding;
    r.union(left, top, right, bottom);

    invalidate(r);
  }
Return whether or not this tab strip will draw a full-width underline.
This defaults to true if no background is set.

@return true if this tab strip will draw a full-width underline in the
current tab indicator color.
sample/src/main/java/android/support/v4/view/PagerTabStripV22.java