如何知道RecyclerView / LinearLayoutManager是滚动到顶部还是底部？

时间：2015-01-08 13:53:07

标签： android android-recyclerview

目前我正在使用以下代码检查是否应启用SwipeRefreshLayout。

private void laySwipeToggle() {
    if (mRecyclerView.getChildCount() == 0 || mRecyclerView.getChildAt(0).getTop() == 0) {
        mLaySwipe.setEnabled(true);
    } else {
        mLaySwipe.setEnabled(false);
    }
}

但这是问题所在。当它滚动到另一个项目时，视图的边界mRecyclerView.getChildAt(0).getTop()也会返回0.

The problem

有RecyclerView.isScrolledToBottom()或RecyclerView.isScrolledToTop()吗？

编辑：(mRecyclerView.getChildAt(0).getTop() == 0 && linearLayoutManager.findFirstVisibleItemPosition() == 0)类似于RecyclerView.isScrolledToTop()，但是RecyclerView.isScrolledToBottom()怎么办？

11 个答案:

答案 0 :(得分：97)

解决方案在布局管理器中。

LinearLayoutManager layoutManager = new LinearLayoutManager(this);

// Add this to your Recycler view
recyclerView.setLayoutManager(layoutManager);

// To check if at the top of recycler view
if(layoutManager.firstCompletelyVisibleItemPosition()==0){
    // Its at top
}

// To check if at the bottom of recycler view
if(layoutManager.lastCompletelyVisibleItemPosition()==data.size()-1){
    // Its at bottom
}

修改

如果您的项目尺寸大于屏幕，请使用以下内容检测顶部事件。

RecyclerView recyclerView = (RecyclerView) view;
LinearLayoutManager linearLayoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();

int pos = linearLayoutManager.findFirstVisibleItemPosition();

if(linearLayoutManager.findViewByPosition(pos).getTop()==0 && pos==0){
    return true;
}

PS：实际上，如果您将RecyclerView直接放在SwipeRefreshview内，则不需要这样做

答案 1 :(得分：53)

如果你只是想知道是否可以滚动

，你可以试试recyclerView.canScrollVertically(int direction)

答案 2 :(得分：32)

检查RecyclerView是否滚动到底部。使用以下代码。

/**
     * Check whether the last item in RecyclerView is being displayed or not
     *
     * @param recyclerView which you would like to check
     * @return true if last position was Visible and false Otherwise
     */
    private boolean isLastItemDisplaying(RecyclerView recyclerView) {
        if (recyclerView.getAdapter().getItemCount() != 0) {
            int lastVisibleItemPosition = ((LinearLayoutManager) recyclerView.getLayoutManager()).findLastCompletelyVisibleItemPosition();
            if (lastVisibleItemPosition != RecyclerView.NO_POSITION && lastVisibleItemPosition == recyclerView.getAdapter().getItemCount() - 1)
                return true;
        }
        return false;
    }

一些其他信息

如果您想在ScrollToBottom RecyclerView Edittext tapped时实施 edittext.setOnTouchListener(new View.OnTouchListener() { @Override public boolean onTouch(View v, MotionEvent event) { if (event.getAction() == MotionEvent.ACTION_UP) if (isLastItemDisplaying(recyclerView)) { // The scrolling can happen instantly before keyboard even opens up so to handle that we add 1 second delay to scrolling recyclerView.postDelayed(new Runnable() { @Override public void run() { recyclerView.smoothScrollToPosition(recyclerView.getAdapter().getItemCount() - 1); } }, 1000); } return false; } }); ，那么我建议您添加 1秒延迟，如下所示：< / p> 

        public static ICollection<System.Data.Entity.Core.Objects.DataClasses.EntityObject> DtToEntity(DataTable DataTable,System.Data.Entity.Core.Objects.DataClasses.EntityObject EntityObject)
    {
        ICollection<System.Data.Entity.Core.Objects.DataClasses.EntityObject> _list = null;
        System.Data.Entity.Core.Objects.DataClasses.EntityObject _tempClass;
        foreach (DataRow dataRow in DataTable.Rows)
        {
            foreach(DataColumn dataColumn in DataTable.Columns)
            {
                foreach (var attribute in EntityObject.GetType().GetProperties())
                {
                    if (attribute.Name == dataColumn.ColumnName && attribute.GetType().Equals(dataColumn.GetType()))
                    {
                        return _list;
                    }
                }
            }


        }

答案 3 :(得分：20)

@Saren Arterius，使用 RecycleView 的 addOnScrollListener ，您可以找到如下所示的Vertical RecycleView的滚动顶部或底部，

RecyclerView rv = (RecyclerView)findViewById(R.id.rv);

rv.addOnScrollListener(new RecyclerView.OnScrollListener() {

            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
            }

            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {

                if (dy < 0) {
                    // Recycle view scrolling up...

                } else if (dy > 0) {
                    // Recycle view scrolling down...
                }
            }
        });

答案 4 :(得分：5)

只需保留对layoutManager的引用，并在您的回收站视图上设置onScrollListener 

mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);

        visibleItemCount = mRecyclerView.getChildCount();
        totalItemCount = mLayoutManager.getItemCount();
        firstVisibleItemIndex = mLayoutManager.findFirstVisibleItemPosition();

        //synchronizew loading state when item count changes
        if (loading) {
            if (totalItemCount > previousTotal) {
                loading = false;
                previousTotal = totalItemCount;
            }
        }
        if (!loading)
            if ((totalItemCount - visibleItemCount) <= firstVisibleItemIndex) {
                // Loading NOT in progress and end of list has been reached
                // also triggered if not enough items to fill the screen
                // if you start loading
                loading = true;
            } else if (firstVisibleItemIndex == 0){
                // top of list reached
                // if you start loading
                loading = true;
            }
        }
    }
});

答案 5 :(得分：5)

使用 recyclerView.canScrollVertically（int方向）检查滚动的顶部还是底部。

方向= 1（向下滚动）（底部）

方向= -1（向上滚动）（顶部）

如果方法返回false，则表示您到达顶部还是底部取决于方向。

答案 6 :(得分：3)

您可以使用以下

检测top 
 recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {

        @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
          }

        @Override
        public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
            super.onScrollStateChanged(recyclerView, newState);
            if(IsRecyclerViewAtTop())
            {
                //your recycler view reached Top do some thing
             }
        }
    });

  private boolean IsRecyclerViewAtTop()   {
        if(recyclerView.getChildCount() == 0)
            return true;
        return recyclerView.getChildAt(0).getTop() == 0;
    }

一旦到达顶部时释放手指，这将检测到顶部， 如果您希望尽快检测到再次访问者if(IsRecyclerViewAtTop())方法

内的最高检查onScrolled

答案 7 :(得分：2)

我写了一个RecyclerViewHelper来了解Recyclerview是在顶部还是在底部。

public class RecyclerViewHelper {
public static boolean isAtTop(RecyclerView recyclerView) {
    if (android.os.Build.VERSION.SDK_INT < Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
        return isAtTopBeforeIceCream(recyclerView);
    } else {
        return !ViewCompat.canScrollVertically(recyclerView, -1);
    }
}

private static boolean isAtTopBeforeIceCream(RecyclerView recyclerView) {
    RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
    if (layoutManager instanceof LinearLayoutManager) {
        LinearLayoutManager linearLayoutManager = (LinearLayoutManager) layoutManager;
        int pos = linearLayoutManager.findFirstVisibleItemPosition();
        if (linearLayoutManager.findViewByPosition(pos).getTop() == recyclerView.getPaddingTop() && pos == 0)
            return true;
    }
    return false;
}


public static boolean isAtBottom(RecyclerView recyclerView) {
    if (android.os.Build.VERSION.SDK_INT < Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
        return isAtBottomBeforeIceCream(recyclerView);
    } else {
        return !ViewCompat.canScrollVertically(recyclerView, 1);
    }
}

private static boolean isAtBottomBeforeIceCream(RecyclerView recyclerView) {
    RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
    int count = recyclerView.getAdapter().getItemCount();
    if (layoutManager instanceof LinearLayoutManager) {
        LinearLayoutManager linearLayoutManager = (LinearLayoutManager) layoutManager;
        int pos = linearLayoutManager.findLastVisibleItemPosition();
        int lastChildBottom = linearLayoutManager.findViewByPosition(pos).getBottom();
        if (lastChildBottom == recyclerView.getHeight() - recyclerView.getPaddingBottom() && pos == count - 1)
            return true;
    }
    return false;
}

}

答案 8 :(得分：2)

你可以这样做，它为我工作

      mRecycleView.addOnScrollListener(new RecyclerView.OnScrollListener() {
        @Override
        public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
            super.onScrollStateChanged(recyclerView, newState);
            }
        }

            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
                int topRowVerticalPosition = (recyclerView == null || recyclerView.getChildCount() == 0) ?
                        0 : recyclerView.getChildAt(0).getTop();
                LinearLayoutManager linearLayoutManager1 = (LinearLayoutManager) recyclerView.getLayoutManager();
                int firstVisibleItem = linearLayoutManager1.findFirstVisibleItemPosition();
                swipeRefreshLayout.setEnabled(firstVisibleItem == 0 && topRowVerticalPosition >= 0);
            }
        });

答案 9 :(得分：1)

您可以尝试使用OnTouchListener：

recyclerView.addOnItemTouchListener(new RecyclerView.OnItemTouchListener() {
    @Override
    public boolean onInterceptTouchEvent(RecyclerView rv, MotionEvent e) {
        if (e.getAction() == MotionEvent.ACTION_UP
            || e.getAction() == MotionEvent.ACTION_MOVE){
        if (mLinearLayoutManager.findFirstCompletelyVisibleItemPosition() > 0)
        {
        // beginning of the recycler 
        }

        if (mLinearLayoutManager.findLastCompletelyVisibleItemPosition()+1 < recyclerView.getAdapter().getItemCount())
        {
        // end of the recycler 
        }         
     }             
return false;
}

答案 10 :(得分：0)

要确定RecyclerView是否滚动到底部，您可以重复使用滚动条所用的方法。

这是计算，为方便起见，写成Kotlin扩展函数： 

fun RecyclerView.isScrolledToBottom(): Boolean {
    val contentHeight = height - (paddingTop + paddingBottom)
    return computeVerticalScrollRange() == computeVerticalScrollOffset() + contentHeight
}
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