要解决这个分页问题,​​请参阅我在post中的回答,其中我已逐步解释了如何从较小的块中加载Cloud Firestore数据库中的数据,并在按钮单击时将其显示在ListView中.

解：

要从Firestore数据库获取数据并在RecyclerView中以较小的块显示,请按照以下步骤操作.

我们来看上面使用过产品的例子.您可以使用产品,城市或任何您想要的东西.原则是一样的.假设您想在用户滚动时加载更多产品,我将使用RecyclerView.OnScrollListener.

让我们首先定义RecyclerView并设置布局管理器：

RecyclerView recyclerView = findViewById(R.id.recycler_view);
recyclerView.setLayoutManager(new LinearLayoutManager(this));

假设我们有一个如下所示的数据库结构：

Firestore-root
   |
   --- products (collection)
         |
         --- productId (document)
                |
                --- productName: "Product Name"

一个看起来像这样的模型类：

public class ProductModel {
    private String productName;
 
    public ProductModel() {}
 
    public ProductModel(String productName) {this.productName = productName;}
 
    public String getProductName() {return productName;}
}

这个适配器类应该是这样的：

private class ProductAdapter extends RecyclerView.Adapter<ProductViewHolder> {
    private List<ProductModel> list;
 
    ProductAdapter(List<ProductModel> list) {
        this.list = list;
    }
 
    @NonNull
    @Override
    public ProductViewHolder onCreateViewHolder(@NonNull ViewGroup parent,int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_product,parent,false);
        return new ProductViewHolder(view);
    }
 
    @Override
    public void onBindViewHolder(@NonNull ProductViewHolder productViewHolder,int position) {
        String productName = list.get(position).getProductName();
        productViewHolder.setProductName(productName);
    }
 
    @Override
    public int getItemCount() {
        return list.size();
    }
}

item_product布局仅包含一个视图,即TextView.

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/text_view"
    android:textSize="25sp"/>

这就是持有者类应该是这样的：

private class ProductViewHolder extends RecyclerView.ViewHolder {
    private View view;
 
    ProductViewHolder(View itemView) {
        super(itemView);
        view = itemView;
    }
 
    void setProductName(String productName) {
        TextView textView = view.findViewById(R.id.text_view);
        textView.setText(productName);
    }
}

现在,让我们将限制定义为全局变量并将其设置为15.

private int limit = 15;

现在让我们使用这个限制来定义查询：

FirebaseFirestore rootRef = FirebaseFirestore.getInstance();
CollectionReference productsRef = rootRef.collection("products");
Query firstQuery = productsRef.orderBy("productName",Query.Direction.ASCENDING).limit(limit);

以下是在您的案例中也具有魔力的代码：

query.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
    @Override
    public void onComplete(@NonNull Task<QuerySnapshot> task) {
        if (task.isSuccessful()) {
            List<ProductModel> list = new ArrayList<>();
            for (DocumentSnapshot document : task.getResult()) {
                ProductModel productModel = document.toObject(ProductModel.class);
                list.add(productModel);
            }
            ProductAdapter productAdapter = new ProductAdapter(list);
            recyclerView.setAdapter(productAdapter);
            lastVisible = task.getResult().getDocuments().get(task.getResult().size() - 1);
 
            RecyclerView.OnScrollListener onScrollListener = new RecyclerView.OnScrollListener() {
                @Override
                public void onScrollStateChanged(RecyclerView recyclerView,int newState) {
                    super.onScrollStateChanged(recyclerView,newState);
                    if (newState == AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL) {
                        isScrolling = true;
                    }
                }
 
                @Override
                public void onScrolled(RecyclerView recyclerView,int dx,int dy) {
                    super.onScrolled(recyclerView,dx,dy);
 
                    LinearLayoutManager linearLayoutManager = ((LinearLayoutManager) recyclerView.getLayoutManager());
                    int firstVisibleItemPosition = linearLayoutManager.findFirstVisibleItemPosition();
                    int visibleItemCount = linearLayoutManager.getChildCount();
                    int totalItemCount = linearLayoutManager.getItemCount();
 
                    if (isScrolling && (firstVisibleItemPosition + visibleItemCount == totalItemCount) && !isLastItemReached) {
                        isScrolling = false;
                        Query nextQuery = productsRef.orderBy("productName",Query.Direction.ASCENDING).startAfter(lastVisible).limit(limit);
                        nextQuery.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                            @Override
                            public void onComplete(@NonNull Task<QuerySnapshot> t) {
                                if (t.isSuccessful()) {
                                    for (DocumentSnapshot d : t.getResult()) {
                                        ProductModel productModel = d.toObject(ProductModel.class);
                                        list.add(productModel);
                                    }
                                    productAdapter.notifyDataSetChanged();
                                    lastVisible = t.getResult().getDocuments().get(t.getResult().size() - 1);
 
                                    if (t.getResult().size() < limit) {
                                        isLastItemReached = true;
                                    }
                                }
                            }
                        });
                    }
                }
            };
            recyclerView.addOnScrollListener(onScrollListener);
        }
    }
});

其中lastVisible是DocumentSnapshot对象,它表示查询中的最后一个visibile项.在这种情况下,每15个一个,它被声明为gloabl变量：

private DocumentSnapshot lastVisible;

isScrolling和isLastItemReached也是全局变量,声明为：

private boolean isScrolling = false;
private boolean isLastItemReached = false;