悬浮吸顶效果，赋予Android RecyclerView新高度！

2023-09-05 14:17:29

前言

在我们的日常开发中，经常会遇到需要在RecyclerView中实现列表分组的情况。而为了让分组更加清晰直观，我们可以通过实现头部悬浮吸顶的效果来突出分组。本篇文章，我就来与大家分享如何在Android RecyclerView中实现头部悬浮吸顶效果，希望对大家有所帮助。

悬浮吸顶效果的实现

1. 首先，我们需要创建一个自定义的LayoutManager。

public class StickyHeaderLayoutManager extends LinearLayoutManager {

    private static final String TAG = "StickyHeaderLayoutManager";

    public StickyHeaderLayoutManager(Context context) {
        super(context);
    }

    public StickyHeaderLayoutManager(Context context, int orientation, boolean reverseLayout) {
        super(context, orientation, reverseLayout);
    }

    @Override
    public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
        super.onLayoutChildren(recycler, state);

        // 获取第一个可见的Item
        View firstVisibleItem = findFirstVisibleItemAndScrollOffset(null);
        if (firstVisibleItem == null) {
            return;
        }

        // 获取第一个可见的Item的Position
        int firstVisibleItemPosition = findFirstVisibleItemPosition();

        // 获取第一个可见的Item的GroupPosition
        int firstVisibleItemGroupPosition = getGroupPositionForItemPosition(firstVisibleItemPosition);

        // 获取悬浮的头部的View
        View stickyHeaderView = recycler.getViewForPosition(firstVisibleItemGroupPosition);

        // 将悬浮的头部的View添加到RecyclerView中
        addStickyHeaderView(stickyHeaderView);

        // 设置悬浮的头部的View的LayoutParams
        LayoutParams layoutParams = (LayoutParams) stickyHeaderView.getLayoutParams();
        layoutParams.topMargin = getTopDecorationHeight(firstVisibleItemPosition);
        stickyHeaderView.setLayoutParams(layoutParams);
    }

    // 添加悬浮的头部的View到RecyclerView中
    private void addStickyHeaderView(View stickyHeaderView) {
        if (stickyHeaderView.getParent() != recyclerView) {
            recyclerView.addView(stickyHeaderView);
        }
    }

    // 获取悬浮的头部的View的LayoutParams
    private LayoutParams getLayoutParamsForStickyHeaderView(View stickyHeaderView) {
        return new LayoutParams(stickyHeaderView.getWidth(), stickyHeaderView.getHeight());
    }

    // 获取第一个可见的Item的GroupPosition
    private int getGroupPositionForItemPosition(int itemPosition) {
        for (int i = itemPosition; i >= 0; i--) {
            if (isGroupHeaderPosition(i)) {
                return i;
            }
        }
        return -1;
    }

    // 判断是否是GroupHeaderPosition
    private boolean isGroupHeaderPosition(int position) {
        return position == 0 || getItemViewType(position) != getItemViewType(position - 1);
    }
}

2. 接下来，我们需要创建一个自定义的RecyclerView.Adapter。

public class StickyHeaderAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    private List<Item> items;

    public StickyHeaderAdapter(List<Item> items) {
        this.items = items;
    }

    @Override
    public int getItemViewType(int position) {
        if (isGroupHeaderPosition(position)) {
            return TYPE_HEADER;
        } else {
            return TYPE_ITEM;
        }
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if (viewType == TYPE_HEADER) {
            return new HeaderViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item_header, parent, false));
        } else {
            return new ItemViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item, parent, false));
        }
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if (holder instanceof HeaderViewHolder) {
            HeaderViewHolder headerViewHolder = (HeaderViewHolder) holder;
            headerViewHolder.textView.setText(items.get(position).getHeader());
        } else if (holder instanceof ItemViewHolder) {
            ItemViewHolder itemViewHolder = (ItemViewHolder) holder;
            itemViewHolder.textView.setText(items.get(position).getItem());
        }
    }

    @Override
    public int getItemCount() {
        return items.size();
    }

    // 判断是否是GroupHeaderPosition
    private boolean isGroupHeaderPosition(int position) {
        return position == 0 || getItemViewType(position) != getItemViewType(position - 1);
    }

    public class HeaderViewHolder extends RecyclerView.ViewHolder {

        public TextView textView;

        public HeaderViewHolder(View itemView) {
            super(itemView);
            textView = (TextView) itemView.findViewById(R.id.textView);
        }
    }

    public class ItemViewHolder extends RecyclerView.ViewHolder {

        public TextView textView;

        public ItemViewHolder(View itemView) {
            super(itemView);
            textView = (TextView) itemView.findViewById(R.id.textView);
        }
    }
}

3. 最后，我们在Activity中使用自定义的LayoutManager和Adapter即可。

public class MainActivity extends AppCompatActivity {

    private RecyclerView recyclerView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

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

        List<Item> items = new ArrayList<>();
        for (int i = 0; i < 100; i++) {
            if (i % 10 == 0) {
                items.add(new Item("Group " + i));
            } else {
                items.add(new Item("Item " + i));
            }
        }

        StickyHeaderLayoutManager layoutManager = new StickyHeaderLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);

        StickyHeaderAdapter adapter = new StickyHeaderAdapter(items);
        recyclerView.setAdapter(adapter);
    }

    public class Item {

        private String header;
        private String item;

        public Item(String header) {
            this.header = header;
        }

        public Item(String item) {
            this.item = item;
        }

        public String getHeader() {
            return header;
        }

        public String getItem() {
            return item;
        }
    }
}