精细化曝光策略

public class CardExposureHelper extends RecyclerView.OnScrollListener { //缓存卡片的双向队列  private Deque<BaseHomeCard> deque;  //队列顶部Card的position  private int preFirstExposure;  //队列底部Card的position  private int preLastExposure;  /**   * 处理垂直方向卡片曝光   * @param manager   * @param isUp 是否向上滑动   */  private void onVerticalExposure(LinearLayoutManager manager,boolean isUp) {    int firstVisiblePosition = manager.findFirstVisibleItemPosition();    int lastVisiblePosition = manager.findLastVisibleItemPosition();    //根据曝光比例判断第一个可见卡片是否需要曝光    firstVisiblePosition = isVerticalExposure(firstVisiblePosition)?firstVisiblePosition:firstVisiblePosition+1;    //根据曝光比例判断最后一个可见卡片是否需要曝光    lastVisiblePosition = isVerticalExposure(lastVisiblePosition)?lastVisiblePosition:lastVisiblePosition-1;    //第一次曝光，曝光所有符合曝光比例的Card    if (preFirstExposure==0&&preLastExposure==0){      offerVerticalVisibleQueue(firstVisiblePosition,lastVisiblePosition,true);    }else if (isUp){      //向上滑动，把顶部不可见Card从顶部出队，底部进入可曝光的卡片入队      popVerticalVisibleQueue(preFirstExposure,firstVisiblePosition-1,true);      offerVerticalVisibleQueue(preLastExposure+1,lastVisiblePosition,false);    }else {      //对应向下滑动的策略      popVerticalVisibleQueue(lastVisiblePosition+1,preLastExposure,false);      offerVerticalVisibleQueue(firstVisiblePosition,preFirstExposure-1,true);    }    //更新队列的顶部position和底部position    preFirstExposure = firstVisiblePosition;    preLastExposure = lastVisiblePosition;  }    /**   * 入队操作   * @param start   * @param end   * @param isFirst 是否从顶部入队   */  private void offerVerticalVisibleQueue(int start,int end,boolean isFirst){    if (start>=0 && end<recyclerView.getAdapter().getItemCount() && start<=end){      if (isFirst){        for (int i=end;i>=start;i--){          onVerticalItemSlideInto(i,true);        }      }else {        for (int i=start;i<=end;i++){          onVerticalItemSlideInto(i,false);        }      }    }  }   /**   * 出队操作   * @param start   * @param end   * @param isFirst 是否从顶部出队   */  private void popVerticalVisibleQueue(int start,int end,boolean isFirst){    if (start>=0 && end<recyclerView.getAdapter().getItemCount() && start<=end){      if (isFirst){        for (int i=start;i<=end;i++){          onVerticalItemSlideOut(i,isFirst);        }      }else {        for (int i=end;i>=start;i--){          onVerticalItemSlideOut(i,isFirst);        }      }    }  }   /**   * 处理滑入（入队）可曝光的卡片   * @param position   * @param isFirst 是否从顶部滑入（入队）   */  private void onVerticalItemSlideInto(int position,boolean isFirst){    BaseHomeCard card = getBaseHomeCard(position);    if (isFirst){      deque.offerFirst(card);    }else {      deque.offerLast(card);    }    //回调卡片开始曝光事件    callItemExposure(card,position);  }    /**   * 处理滑出（出队）停止曝光的卡片   * @param position   * @param isFirst 是否从顶部滑出（出队）   */  private void onVerticalItemSlideOut(int position,boolean isFirst){    BaseHomeCard card;    if (isFirst){      card = deque.removeFirst();    }else {      card = deque.removeLast();    }    //回调卡片结束曝光事件    callItemEndExposure(card,position,isFirst);  }