如果RecycleView的高度不在屏幕上，则项目装饰显示在最后一行下方

Question

如果我将RecycleView与垂直GridLayoutManager或StaggeredGridLayoutManager一起使用，当RecycleView的高度未在屏幕上时，装饰将显示在最后一行下方（这不是我想要的）

我认为getItemOffset()方法可能有问题吗？ 这是装饰代码：

 @Override
public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
    drawHorizontal(c, parent);
    drawVertical(c, parent);
}

private void drawHorizontal(Canvas c, RecyclerView parent) {
    int childCount = parent.getChildCount();
    for (int i = 0; i < childCount; i++) {
        final View child = parent.getChildAt(i);
        final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                .getLayoutParams();
        final int left = child.getLeft() - params.leftMargin;
        final int right = child.getRight() + params.rightMargin + dividerSize;
        final int top = child.getBottom() + params.bottomMargin;
        final int bottom = top + dividerSize;
        divider.setBounds(left, top, right, bottom);
        divider.draw(c);
    }
}

private void drawVertical(Canvas c, RecyclerView parent) {
    final int childCount = parent.getChildCount();
    for (int i = 0; i < childCount; i++) {
        final View child = parent.getChildAt(i);
        final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                .getLayoutParams();
        final int top = child.getTop() - params.topMargin;
        final int bottom = child.getBottom() + params.bottomMargin;
        final int left = child.getRight() + params.rightMargin;
        final int right = left + dividerSize;
        divider.setBounds(left, top, right, bottom);
        divider.draw(c);
    }
}

@Override
public void getItemOffsets(Rect outRect,
                           View view,
                           RecyclerView parent,
                           RecyclerView.State state) {
    int spanCount = getSpanCount(parent);
    int childCount = parent.getAdapter().getItemCount();
    int itemPosition = parent.getChildAdapterPosition(view);
    if (isLastRaw(parent, itemPosition, spanCount, childCount) &&
            isLastColum(parent, itemPosition, spanCount, childCount)) {
        outRect.set(0, 0, 0, 0);
    } else if (isLastRaw(parent, itemPosition, spanCount, childCount)) {
        outRect.set(0, 0, dividerSize, 0);
    } else if (isLastColum(parent, itemPosition, spanCount, childCount)) {
        outRect.set(0, 0, 0, dividerSize);
    } else {
        outRect.set(0, 0, dividerSize, dividerSize);
    }
}

private int getSpanCount(RecyclerView parent) {
    int spanCount = -1;
    RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
    if (layoutManager instanceof GridLayoutManager) {
        spanCount = ((GridLayoutManager) layoutManager).getSpanCount();
    } else if (layoutManager instanceof StaggeredGridLayoutManager) {
        spanCount = ((StaggeredGridLayoutManager) layoutManager).getSpanCount();
    }
    return spanCount;
}

private boolean isLastColum(RecyclerView parent, int position, int spanCount, int childCount) {
    RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
    if (layoutManager instanceof GridLayoutManager) {
        if ((position + 1) % spanCount == 0) {
            return true;
        }
    } else if (layoutManager instanceof StaggeredGridLayoutManager) {
        int orientation = ((StaggeredGridLayoutManager) layoutManager).getOrientation();
        if (orientation == StaggeredGridLayoutManager.VERTICAL) {
            if ((position + 1) % spanCount == 0) {
                return true;
            }
        } else {
            int columCount = childCount / spanCount;
            if (childCount % columCount == 0) {
                if (position + 1 > childCount - spanCount) {
                    return true;
                }
            } else {
                if (position + 1 > childCount - childCount % columCount) {
                    return true;
                }
            }
        }
    }
    return false;
}

private boolean isLastRaw(RecyclerView parent, int position, int spanCount, int childCount) {
    RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
    if (layoutManager instanceof GridLayoutManager) {
        int rawCount = childCount % spanCount == 0 ?
                childCount / spanCount :
                childCount / spanCount + 1;
        int lastRawFirstPosition = rawCount * spanCount - spanCount + 1;
        if (position + 1 >= lastRawFirstPosition) {
            return true;
        }
    } else if (layoutManager instanceof StaggeredGridLayoutManager) {
        int orientation = ((StaggeredGridLayoutManager) layoutManager).getOrientation();
        if (orientation == StaggeredGridLayoutManager.VERTICAL) {
            int rawCount = childCount % spanCount == 0 ?
                    childCount / spanCount :
                    childCount / spanCount + 1;
            int lastRawFirstPosition = rawCount * spanCount - spanCount + 1;
            if (position + 1 >= lastRawFirstPosition) {
                return true;
            }
        } else {
            if ((position + 1) % spanCount == 0) {
                return true;
            }
        }
    }
    return false;
}

当RecycleView的高度超过屏幕时，RecycleView的底部：

当RecycleView的高度未超过屏幕时，RecycleView的底部：