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目录
项目中的案例【预加载】
项目中的另一个案例
利用 lastVisibleItemPosition 判断【不靠谱】
利用 computeVerticalScrollRange 等判断【不靠谱】
利用 canScrollVertically(direction) 判断【比较靠谱】
利用 LinearLayoutManager 来判断【垃圾】

mRvChat.addOnScrollListener(new RecyclerView.OnScrollListener() {private int minLeftItemCount=10;//剩余多少条时开始加载更多@Overridepublic void onScrolled(RecyclerView recyclerView, int dx, int dy) {if (recyclerView.getLayoutManager() instanceof LinearLayoutManager) {LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();int itemCount = layoutManager.getItemCount();int lastPosition = layoutManager.findLastCompletelyVisibleItemPosition();XLog.tag("bqt3").i("【总数】" + itemCount + "【位置】" + lastPosition);if (lastPosition == layoutManager.getItemCount() - 1) {//容错处理，保证滑到最后一条时一定可以加载更多this.onLoadMore();} else {if (itemCount > minLeftItemCount) {if (lastPosition == itemCount - minLeftItemCount) {//一定要意识到，onScrolled方法并不是一直被回调的，估计最多一秒钟几十次//所以当此条件满足时，可能并没有回调onScrolled方法，也就不会调用onLoadMore方法//所以一定要想办法弥补这隐藏的bug，最简单的方式就是当滑到最后一条时一定可以加载更多this.onLoadMore();}} else {//（第一次进入时）如果总数特别少，直接加载更多this.onLoadMore();}}}}private void onLoadMore() {if (canLoadMore) {canLoadMore = false;ChatReqHelper.requestGroupHis(groupId, ((ChatModel) mGroupChats.get(mGroupChats.size() - 1)).getMsgId());XLog.tag("bqt3").i("【加载更多数据】");}}
});

rv.addOnScrollListener(new RecyclerView.OnScrollListener() {@Overridepublic void onScrolled(RecyclerView recyclerView, int dx, int dy) {super.onScrolled(recyclerView, dx, dy);StaggeredGridLayoutManager layoutManager = (StaggeredGridLayoutManager) rv.getLayoutManager();int[] positions = layoutManager.findLastVisibleItemPositions(null);if (positions != null && positions.length > 0) {for (int position : positions) {if (position >= mDatas.size() - layoutManager.getSpanCount() || !rv.canScrollVertically(1)) {//滑到底部了if (canLoadMore) {XLog.tag("bqt_red").i("加载更多 "+position+" "+rv.canScrollVertically(1));canLoadMore = false;doRequest();}break;}}}}
});

public static boolean isVisBottom(RecyclerView recyclerView){  LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();  int lastVisibleItemPosition = layoutManager.findLastVisibleItemPosition(); //屏幕中最后一个可见子项的positionint visibleItemCount = layoutManager.getChildCount(); //当前屏幕所看到的子项个数int totalItemCount = layoutManager.getItemCount(); //当前RecyclerView的所有子项个数int state = recyclerView.getScrollState(); //RecyclerView的滑动状态if(visibleItemCount > 0 && lastVisibleItemPosition == totalItemCount - 1 && state == recyclerView.SCROLL_STATE_IDLE){   return true; }else {   return false;  }
}

public static boolean isSlideToBottom(RecyclerView recyclerView) {return recyclerView != null&& recyclerView.computeVerticalScrollExtent()//当前屏幕显示区域的高度+ recyclerView.computeVerticalScrollOffset()//当前屏幕之前滑过的距离>= recyclerView.computeVerticalScrollRange();//整个View控件的高度
}

/*** Check if this view can be scrolled vertically in a certain direction.** @param direction Negative to check scrolling up, positive to check scrolling down.* @return true if this view can be scrolled in the specified direction, false otherwise.*/
public boolean canScrollVertically(int direction) {final int offset = computeVerticalScrollOffset();final int range = computeVerticalScrollRange() - computeVerticalScrollExtent();if (range == 0) return false;if (direction < 0) {return offset > 0;} else {return offset < range - 1;}
}

public static int getItemHeight(RecyclerView recyclerView) {int itemHeight = 0;View child = null;LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();int firstPos = layoutManager.findFirstCompletelyVisibleItemPosition();int lastPos = layoutManager.findLastCompletelyVisibleItemPosition();child = layoutManager.findViewByPosition(lastPos);if (child != null) {RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();itemHeight = child.getHeight() + params.topMargin + params.bottomMargin;}return itemHeight;
}

public static int getLinearTotalHeight(RecyclerView recyclerView) {int totalHeight = 0;LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();View child = layoutManager.findViewByPosition(layoutManager.findFirstVisibleItemPosition());int headerCildHeight = getHeaderHeight(recyclerView);if (child != null) {int itemHeight = getItemHeight(recyclerView);int childCount = layoutManager.getItemCount();totalHeight = headerCildHeight + (childCount - 1) * itemHeight;}return totalHeight;
}

public static boolean isLinearBottom(RecyclerView recyclerView) {boolean isBottom = true;int scrollY = getLinearScrollY(recyclerView);int totalHeight = getLinearTotalHeight(recyclerView);int height = recyclerView.getHeight();// Log.e("height","scrollY " + scrollY + " totalHeight " + totalHeight + " recyclerHeight " + height);  if (scrollY + height < totalHeight) {isBottom = false;}return isBottom;
}

public static int getHeaderHeight(RecyclerView recyclerView) {int headerCildHeight = 0;LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();int firstHeaderPos = layoutManager.findFirstCompletelyVisibleItemPosition();View headerCild = layoutManager.findViewByPosition(firstHeaderPos);if (headerCild != null) {RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) headerCild.getLayoutParams();headerCildHeight = headerCild.getHeight() + params.topMargin + params.bottomMargin;}return headerCildHeight;
}

public static int getLinearScrollY(RecyclerView recyclerView) {int scrollY = 0;LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();int headerCildHeight = getHeaderHeight(recyclerView);int firstPos = layoutManager.findFirstVisibleItemPosition();View child = layoutManager.findViewByPosition(firstPos);int itemHeight = getItemHeight(recyclerView);if (child != null) {int firstItemBottom = layoutManager.getDecoratedBottom(child);scrollY = headerCildHeight + itemHeight * firstPos - firstItemBottom;if (scrollY < 0) {scrollY = 0;}}return scrollY;
}