Android上拉加载更多

在Android中实现下拉刷新和上拉加载更多可以使用第三方库，比如SwipeRefreshLayout和RecyclerView，下面是一个简单的示例：

1.在布局文件中添加RecyclerView和SwipeRefreshLayout：

<androidx.swiperefreshlayout.widget.SwipeRefreshLayout
    android:id="@+id/swipeRefreshLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</androidx.swiperefreshlayout.widget.SwipeRefreshLayout>

2.在Activity或Fragment中设置RecyclerView的LayoutManager和Adapter，并为SwipeRefreshLayout设置刷新监听器。示例代码如下：

private RecyclerView recyclerView;
private SwipeRefreshLayout swipeRefreshLayout;
private MyAdapter adapter;
private List<String> dataList = new ArrayList<>();
private int page = 1;

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

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

    // 设置布局管理器
    recyclerView.setLayoutManager(new LinearLayoutManager(this));
    // 设置adapter
    adapter = new MyAdapter(dataList);
    recyclerView.setAdapter(adapter);

    // 设置刷新监听器
    swipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
        @Override
        public void onRefresh() {
            // 下拉刷新操作
            refresh();
        }
    });

    // 设置滑动监听器，实现上拉加载更多
    recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
        @Override
        public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
            LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();
            int lastVisibleItemPosition = layoutManager.findLastVisibleItemPosition();
            int totalItemCount = layoutManager.getItemCount();
            if (lastVisibleItemPosition == totalItemCount - 1 && dy > 0) {
                // 上拉加载更多
                loadMore();
            }
        }
    });

    // 第一次进入页面时自动刷新
    swipeRefreshLayout.post(new Runnable() {
        @Override
        public void run() {
            swipeRefreshLayout.setRefreshing(true);
            refresh();
        }
    });
}

// 下拉刷新
private void refresh() {
    page = 1;
    dataList.clear();
    getDataList();
}

// 上拉加载更多
private void loadMore() {
    page++;
    getDataList();
}

// 模拟获取数据
private void getDataList() {
    new Handler().postDelayed(new Runnable() {
        @Override
        public void run() {
            for (int i = 0; i < 20; i++) {
                dataList.add("item " + (dataList.size() + 1));
            }
            adapter.notifyDataSetChanged();
            swipeRefreshLayout.setRefreshing(false);
        }
    }, 2000);
}

在上述代码中，refresh()方法用于下拉刷新，loadMore()方法用于上拉加载更多，getDataList()方法用于获取数据。在getDataList()方法中，我们使用Handler模拟了一个异步任务，通过adapter.notifyDataSetChanged()方法来更新RecyclerView的显示。