void updateAdapter(PagerAdapter oldAdapter, PagerAdapter newAdapter) {
   if (oldAdapter != null) {
     oldAdapter.unregisterDataSetObserver(mPageListener);
   }
   if (newAdapter != null) {
     newAdapter.registerDataSetObserver(mPageListener);
   }
   if (mPager != null) {
     mLastKnownCurrentPage = -1;
     mLastKnownPositionOffset = -1;
     updateText(mPager.getCurrentItem(), newAdapter);
     requestLayout();
   }
 }
  void updateTextPositions(int position, float positionOffset) {
    if (position != mLastKnownCurrentPage) {
      updateText(position, mPager.getAdapter());
    } else if (positionOffset == mLastKnownPositionOffset) {
      return;
    }

    mUpdatingPositions = true;

    final int prevWidth = mPrevText.getMeasuredWidth();
    final int currWidth = mCurrText.getMeasuredWidth();
    final int nextWidth = mNextText.getMeasuredWidth();
    final int halfCurrWidth = currWidth / 2;

    final int stripWidth = getWidth();
    final int paddingLeft = getPaddingLeft();
    final int paddingRight = getPaddingRight();
    final int paddingTop = getPaddingTop();
    final int textPaddedLeft = paddingLeft + halfCurrWidth;
    final int textPaddedRight = paddingRight + halfCurrWidth;
    final int contentWidth = stripWidth - textPaddedLeft - textPaddedRight;

    float currOffset = positionOffset + 0.5f;
    if (currOffset > 1.f) {
      currOffset -= 1.f;
    }
    final int currCenter = stripWidth - textPaddedRight - (int) (contentWidth * currOffset);
    final int currLeft = currCenter - currWidth / 2;
    final int currRight = currLeft + currWidth;

    mCurrText.layout(currLeft, paddingTop, currRight, paddingTop + mCurrText.getMeasuredHeight());

    final int prevLeft = Math.min(paddingLeft, currLeft - mScaledTextSpacing - prevWidth);
    mPrevText.layout(
        prevLeft, paddingTop, prevLeft + prevWidth, paddingTop + mPrevText.getMeasuredHeight());

    final int nextLeft =
        Math.max(stripWidth - paddingRight - nextWidth, currRight + mScaledTextSpacing);
    mNextText.layout(
        nextLeft, paddingTop, nextLeft + nextWidth, paddingTop + mNextText.getMeasuredHeight());

    mLastKnownPositionOffset = positionOffset;
    mUpdatingPositions = false;
  }