android - 如何在recyclerview中实现粘性页脚

Question

我有 RecyclerView，我需要下一个行为:

• 如果有很多项目(超过屏幕大小) - 页脚是最后一个项目
• 如果项目很少/没有项目 - 页脚位于屏幕底部

请告知我该如何实现此行为。

Answer 1

您可以使用 RecyclerView.ItemDecoration 来实现此行为。

public class StickyFooterItemDecoration extends RecyclerView.ItemDecoration {

    /**
     * Top offset to completely hide footer from the screen and therefore avoid noticeable blink during changing position of the footer.
     */
    private static final int OFF_SCREEN_OFFSET = 5000;

    @Override
    public void getItemOffsets(Rect outRect, final View view, final RecyclerView parent, RecyclerView.State state) {
        int adapterItemCount = parent.getAdapter().getItemCount();
        if (isFooter(parent, view, adapterItemCount)) {
            //For the first time, each view doesn't contain any parameters related to its size,
            //hence we can't calculate the appropriate offset.
            //In this case, set a big top offset and notify adapter to update footer one more time.
            //Also, we shouldn't do it if footer became visible after scrolling.
            if (view.getHeight() == 0 && state.didStructureChange()) {
                hideFooterAndUpdate(outRect, view, parent);
            } else {
                outRect.set(0, calculateTopOffset(parent, view, adapterItemCount), 0, 0);
            }
        }
    }

    private void hideFooterAndUpdate(Rect outRect, final View footerView, final RecyclerView parent) {
        outRect.set(0, OFF_SCREEN_OFFSET, 0, 0);
        footerView.post(new Runnable() {
            @Override
            public void run() {
                parent.getAdapter().notifyDataSetChanged();
            }
        });
    }

    private int calculateTopOffset(RecyclerView parent, View footerView, int itemCount) {
        int topOffset = parent.getHeight() - visibleChildsHeightWithFooter(parent, footerView, itemCount);
        return topOffset < 0 ? 0 : topOffset;
    }

    private int visibleChildsHeightWithFooter(RecyclerView parent, View footerView, int itemCount) {
        int totalHeight = 0;
        //In the case of dynamic content when adding or removing are possible itemCount from the adapter is reliable,
        //but when the screen can fit fewer items than in adapter, getChildCount() from RecyclerView should be used.
        int onScreenItemCount = Math.min(parent.getChildCount(), itemCount);
        for (int i = 0; i < onScreenItemCount - 1; i++) {
            totalHeight += parent.getChildAt(i).getHeight();
        }
        return totalHeight + footerView.getHeight();
    }

    private boolean isFooter(RecyclerView parent, View view, int itemCount) {
        return parent.getChildAdapterPosition(view) == itemCount - 1;
    }
}

确保为 RecyclerView 高度设置 ma​​tch_parent。

请查看示例应用程序 https://github.com/JohnKuper/recyclerview-sticky-footer以及它是如何工作的http://sendvid.com/nbpj0806

此解决方案的一个巨大缺点是它仅在 notifyDataSetChanged() 整个应用程序(而不是内部装饰)之后才能正常工作。对于更具体的通知，它将无法正常工作并支持它们，它需要更多的逻辑。此外，您还可以从 eowise 的库 recyclerview-stickyheaders 中获得见解并改进此解决方案。