mode sbo style osi set vertica 條件 pos cif

判斷RecyclerView到達底部的幾種方法

項目中的案例

mRvChat.addOnScrollListener(new RecyclerView.OnScrollListener() {
	private int minLeftItemCount=10;//剩余多少條時開始加載更多
	@Override
	public 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("【總數】" + itemCount + "【位置】" + lastPosition);
			if (lastPosition == layoutManager.getItemCount
 
() - 1) {//容錯處理，保證滑到最後一條時一定可以加載更多
				this.onLoadMore();
			} else {
				if (itemCount > minLeftItemCount) {
					if (lastPosition == itemCount - minLeftItemCount) {
						//一定要意識到，onScrolled方法並不是一直被回調的，估計最多一秒鐘幾十次
						//所以當此條件滿足時，可能並沒有回調onScrolled方法，也就不會調用onLoadMore方法
						//所以一定要想辦法彌補這隱藏的bug，最簡單的方式就是當滑到最後一條時一定可以加載更多
 
						this.onLoadMore();
					}
				} else {//（第一次進入時）如果總數特別少，直接加載更多
					this.onLoadMore();
				}
			}
		}
	}
	private void onLoadMore() {
		if (canLoadMore) {
			canLoadMore = false;
			ChatReqHelper.requestGroupHis(groupId, ((ChatModel) mGroupChats.get(mGroupChats.size() - 1)).getMsgId());
			XLog.tag("bqt3").i("【加載更多數據】");
		}
	}
});

利用 lastVisibleItemPosition 判斷

簡單判斷

public static boolean isVisBottom(RecyclerView recyclerView){  
  LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();  
  int lastVisibleItemPosition = layoutManager.findLastVisibleItemPosition(); //屏幕中最後一個可見子項的position
  int visibleItemCount = layoutManager.getChildCount(); //當前屏幕所看到的子項個數
  int totalItemCount = layoutManager.getItemCount(); //當前RecyclerView的所有子項個數
  int state = recyclerView.getScrollState(); //RecyclerView的滑動狀態
  if(visibleItemCount > 0 && lastVisibleItemPosition == totalItemCount - 1 && state == recyclerView.SCROLL_STATE_IDLE){   
     return true; 
  }else {   
     return false;  
  }
}

當屏幕中最後一個子項 lastVisibleItemPosition 等於所有子項個數 totalItemCount - 1，那麽RecyclerView就到達了底部。但是，如果 totalItemCount 等於1，並且這個item的高度比屏幕還要高時，我們可以發現這個item沒完全顯示出來就已經被判斷為拉到底部。

利用 computeVerticalScrollRange 等判斷

這種方法原理其實很簡單，而且也是View自帶的方法

public static boolean isSlideToBottom(RecyclerView recyclerView) {
	return recyclerView != null
			&& recyclerView.computeVerticalScrollExtent()//當前屏幕顯示區域的高度
			+ recyclerView.computeVerticalScrollOffset()//當前屏幕之前滑過的距離
			>= recyclerView.computeVerticalScrollRange();//整個View控件的高度
}

這種方法經過測試，暫時還沒發現有bug，而且它用的是View自帶的方法，所以個人覺得比較靠譜。

利用 canScrollVertically(direction) 判斷

這種方法更簡單，就通過簡單的調用方法，就可以得到你想要的結果。這種方法與第二種方法其實是同一種方法，我們看看 canScrollVertically 的源碼：

/**
 * 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;
	}
}

canScrollVertically(1)的值表示是否能向上滾動，true表示能滾動，false表示已經滾動到底部canScrollVertically(-1)的值表示是否能向下滾動，true表示能滾動，false表示已經滾動到頂部

利用 LinearLayoutManager 來判斷

這種方法其實是比較呆板的，就是利用LinearLayoutManager的幾個方法算出已經滑過的子項的距離、屏幕的高度、RecyclerView的總高度，最後將高度作比較。
算出一個子項的高度

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;
}

算出滑過的子項的總距離

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;
}

算出所有子項的總高度

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;
}

其他

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;
}

雖然這種方法看上去比較呆板的同時考慮不很周全，但這種方法可以對RecylerView的LinearLayoutManager有深一步的理解！

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RecyclerView 判斷滑到底/頂部的方法