Android实现网易严选标签栏滑动效果

// 根据当前选定的tab，得到indicator应该移动到的位置 
private Pair<Float, Float> getIndicatorTargetLeftRight(int position, float positionOffset) { 
  View tab = tabsContainer.getChildAt(position); 
  Pair<Float, Float> indicator = getIndicatorLeftRight(tab); 
  float targetLeft = indicator.first; 
  float targetRight = indicator.second; 
  // 如果positionOffset不为0，indicator正处于两个tab之间，需进行加权计算得到它的位置 
  if (positionOffset > 0f && position < tabCount - 1) { 
    View nextTab = tabsContainer.getChildAt(position + 1); 
    Pair<Float, Float> indicatorForNextTab = getIndicatorLeftRight(nextTab); 
    float left = indicatorForNextTab.first; 
    float right = indicatorForNextTab.second; 
    targetLeft = (positionOffset * left + (1f - positionOffset) * targetLeft); 
    targetRight = (positionOffset * right + (1f - positionOffset) * targetRight); 
  } 
  return new Pair<>(targetLeft, targetRight); 
} 
 
private Pair<Float, Float> getIndicatorLeftRight(View tab) { 
  float left = tab.getLeft(); 
  float right = tab.getRight(); 
  if (indicatorMode == IndicatorMode.WRAP && tab instanceof TextView) { 
    TextView tabTextView = (TextView) tab; 
    paint.setTextSize(tabTextView.getTextSize()); 
    float textLength = paint.measureText(tabTextView.getText().toString()); 
    float middle = (left + right) / 2f; 
    left = middle - textLength / 2f; 
    right = middle + textLength / 2f; 
  } 
  return new Pair<>(left, right); 
} 

private boolean isAnimateRunning = false; 
private static final String TARGET_LEFT = "targetLeft"; 
private static final String TARGET_RIGHT = "targetRight"; 
 
private void startIndicatorAnimate(final float targetLeft, final float targetRight) { 
  // 在indicator超出屏幕范围时，让其从屏幕边界处开始移动 
  float move = 0; 
  if (indicatorCurrentRight < getScrollX()) { 
    move = getScrollX() - indicatorCurrentRight; 
  } else if (indicatorCurrentLeft > getScrollX() + DimenUtil.getScreenWidth(getContext())) { 
    move = getScrollX() + DimenUtil.getScreenWidth(getContext()) - indicatorCurrentLeft; 
  } 
  indicatorCurrentLeft += move; 
  indicatorCurrentRight += move; 
 
  PropertyValuesHolder valuesHolderLeft = PropertyValuesHolder.ofFloat( 
      TARGET_LEFT, indicatorCurrentLeft, targetLeft); 
  PropertyValuesHolder valuesHolderRight = PropertyValuesHolder.ofFloat( 
      TARGET_RIGHT, indicatorCurrentRight, targetRight); 
  ValueAnimator animator = ValueAnimator.ofPropertyValuesHolder(valuesHolderLeft, valuesHolderRight) 
      .setDuration(SCROLL_DURATION); 
  animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { 
    @Override 
    public void onAnimationUpdate(ValueAnimator animation) { 
      if (indicatorCurrentLeft != targetLeft) { 
        indicatorCurrentLeft = (float) animation.getAnimatedValue(TARGET_LEFT); 
      } 
      if (indicatorCurrentRight != targetRight) { 
        indicatorCurrentRight = (float) animation.getAnimatedValue(TARGET_RIGHT); 
      } 
      if (indicatorCurrentLeft == targetLeft && indicatorCurrentRight == targetRight) { 
        isAnimateRunning = false; 
      } 
      invalidate(); 
    } 
  }); 
  animator.start(); 
  isAnimateRunning = true; 
}