Android中RecyclerView实现分页滚动的方法详解

 //当前滑动距离
 private int offsetY = 0;
 private int offsetX = 0;
 //按下屏幕点
 private int startY = 0;
 private int startX = 0;
@Override
  public boolean onTouch(View v, MotionEvent event) {
   //手指按下的时候记录开始滚动的坐标
   if (event.getAction() == MotionEvent.ACTION_DOWN) {
    //手指按下的开始坐标
    startY = offsetY;
    startX = offsetX;
   }
   return false;
  }
 }

@Override
 public void scrollTo(int x, int y) {
  Log.w(TAG, "RecyclerView does not support scrolling to an absolute position. "
    + "Use scrollToPosition instead");
 }

/**
 * This class defines the behavior of fling if the developer wishes to handle it.
 * <p>
 * Subclasses of {@link OnFlingListener} can be used to implement custom fling behavior.
 *
 * @see #setOnFlingListener(OnFlingListener)
 */
 public static abstract class OnFlingListener {
  /**
  * Override this to handle a fling given the velocities in both x and y directions.
  * Note that this method will only be called if the associated {@link LayoutManager}
  * supports scrolling and the fling is not handled by nested scrolls first.
  *
  * @param velocityX the fling velocity on the X axis
  * @param velocityY the fling velocity on the Y axis
  *
  * @return true if the fling washandled, false otherwise.
  */
  public abstract boolean onFling(int velocityX, int velocityY);
 }

 //当前滑动距离
 private int offsetY = 0;
 private int offsetX = 0;
 //按下屏幕点
 private int startY = 0;
 private int startX = 0;
 //最后一个可见 view 位置
 private int lastItemPosition = -1;
 //第一个可见view的位置
 private int firstItemPosition = -2;
 //总 itemView 数量
 private int totalNum;
@Override
  public boolean onFling(int velocityX, int velocityY) {
   if (mOrientation == ORIENTATION.NULL) {
    return false;
   }
   //获取开始滚动时所在页面的index
   int page = getStartPageIndex();
   //记录滚动开始和结束的位置
   int endPoint = 0;
   int startPoint = 0;
   //如果是垂直方向
   if (mOrientation == ORIENTATION.VERTICAL) {
    //开始滚动位置，当前开始执行 scrollBy 位置
    startPoint = offsetY;
    if (velocityY < 0) {
     page--;
    } else if (velocityY > 0) {
     page++;
    } else if (pageNum != -1) {
     if (lastItemPosition + 1 == totalNum) {
      mRecyclerView.scrollToPosition(0);
     }
     page = pageNum - 1;
    }
    //更具不同的速度判断需要滚动的方向
    //一次滚动一个 mRecyclerView 高度
    endPoint = page * mRecyclerView.getHeight();
   } else {
    startPoint = offsetX;
    if (velocityX < 0) {
     page--;
    } else if (velocityX > 0) {
     page++;
    } else if (pageNum != -1) {
     if (lastItemPosition + 1 == totalNum) {
      mRecyclerView.scrollToPosition(0);
     }
     page = pageNum - 1;
    }
    endPoint = page * mRecyclerView.getWidth();
   }
   //使用动画处理滚动
   if (mAnimator == null) {
    mAnimator = ValueAnimator.ofInt(startPoint, endPoint);
    mAnimator.setDuration(300);
    mAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
     @Override
     public void onAnimationUpdate(ValueAnimator animation) {
      int nowPoint = (int) animation.getAnimatedValue();
      if (mOrientation == ORIENTATION.VERTICAL) {
       int dy = nowPoint - offsetY;
       if (dy == 0) return;
       //这里通过RecyclerView的scrollBy方法实现滚动。
       mRecyclerView.scrollBy(0, dy);
      } else {
       int dx = nowPoint - offsetX;
       mRecyclerView.scrollBy(dx, 0);
      }
     }
    });
    mAnimator.addListener(new AnimatorListenerAdapter() {
     //动画结束
     @Override
     public void onAnimationEnd(Animator animation) {
      //回调监听
      if (null != mOnPageChangeListener) {
       mOnPageChangeListener.onPageChange(getPageIndex());
      }
      //滚动完成，进行判断是否滚到头了或者滚到尾部了
      RecyclerView.LayoutManager layoutManager = mRecyclerView.getLayoutManager();
      //判断是当前layoutManager是否为LinearLayoutManager
      // 只有LinearLayoutManager才有查找第一个和最后一个可见view位置的方法
      if (layoutManager instanceof LinearLayoutManager) {
       LinearLayoutManager linearManager = (LinearLayoutManager) layoutManager;
       //获取最后一个可见view的位置
       lastItemPosition = linearManager.findLastVisibleItemPosition();
       //获取第一个可见view的位置
       firstItemPosition = linearManager.findFirstVisibleItemPosition();
      }
      totalNum = mRecyclerView.getAdapter().getItemCount();
      if (totalNum == lastItemPosition + 1) {
       updateLayoutManger();
      }
      if (firstItemPosition == 0) {
       updateLayoutManger();
      }
     }
    });
   } else {
    mAnimator.cancel();
    mAnimator.setIntValues(startPoint, endPoint);
   }
   mAnimator.start();
   return true;
  }
 }

public abstract static class OnScrollListener {
  /**
  * Callback method to be invoked when RecyclerView's scroll state changes.
  *
  * @param recyclerView The RecyclerView whose scroll state has changed.
  * @param newState  The updated scroll state. One of {@link #SCROLL_STATE_IDLE},
  *      {@link #SCROLL_STATE_DRAGGING} or {@link #SCROLL_STATE_SETTLING}.
  */
  public void onScrollStateChanged(RecyclerView recyclerView, int newState){}
  /**
  * Callback method to be invoked when the RecyclerView has been scrolled. This will be
  * called after the scroll has completed.
  * <p>
  * This callback will also be called if visible item range changes after a layout
  * calculation. In that case, dx and dy will be 0.
  * 滚动完成调用
  * @param recyclerView The RecyclerView which scrolled.
  * @param dx The amount of horizontal scroll.
  * @param dy The amount of vertical scroll.
  */
  public void onScrolled(RecyclerView recyclerView, int dx, int dy){}
 }

@Override
  public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
   //如果滑动停止
   if (newState == RecyclerView.SCROLL_STATE_IDLE && mOrientation != ORIENTATION.NULL) {
    boolean move;
    int vX = 0, vY = 0;
    if (mOrientation == ORIENTATION.VERTICAL) {
     int absY = Math.abs(offsetY - startY);
     //如果滑动的距离超过屏幕的一半表示需要滑动到下一页
     move = absY > recyclerView.getHeight() / 2;
     vY = 0;
     if (move) {
      vY = offsetY - startY < 0 ? -1000 : 1000;
     }
    } else {
     int absX = Math.abs(offsetX - startX);
     move = absX > recyclerView.getWidth() / 2;
     if (move) {
      vX = offsetX - startX < 0 ? -1000 : 1000;
     }
    }
    //调用滑动
    mOnFlingListener.onFling(vX, vY);
   }
  }
 @Override
  public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
   //滚动结束记录滚动的偏移量
   //记录当前滚动到的位置
   offsetY += dy;
   offsetX += dx;
  }
 }

if (mAnimator == null) {
    mAnimator = ValueAnimator.ofInt(startPoint, endPoint);
    mAnimator.setDuration(300);
    mAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
     @Override
     public void onAnimationUpdate(ValueAnimator animation) {
      int nowPoint = (int) animation.getAnimatedValue();
      if (mOrientation == ORIENTATION.VERTICAL) {
       int dy = nowPoint - offsetY;
       if (dy == 0) return;
       //这里通过RecyclerView的scrollBy方法实现滚动。
       mRecyclerView.scrollBy(0, dy);
      } else {
       int dx = nowPoint - offsetX;
       mRecyclerView.scrollBy(dx, 0);
      }
     }
    });

public void setPageNum(int page) {
 this.pageNum = page;
 mOnFlingListener.onFling(0, 0);
}