如何使用Android对Firestore进行分页？ [英] How to paginate Firestore with Android?
问题描述
我阅读了Firestore文档以及关于Firestore分页的互联网（stackoverflow）上的所有文章，但没有运气。我试图在docs中实现确切的代码，但没有任何反应。我有一个基本的数据库项目（超过1250或更多），我想逐步得到它们。通过滚动来加载15个项目（到数据库中的最后一项）。
I read Firestore documentation and all articles on internet(stackoverflow) about Firestore pagination but no luck. I tried to implement the exact code in docs, but nothing happens. I have a basic database with items(over 1250 or more) and I want to get them progressively. By scrolling to load 15 items (to the last item in the database).
如果使用文档代码：
// Construct query for first 25 cities, ordered by population
Query first = db.collection("cities")
.orderBy("population")
.limit(25);
first.get()
.addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
@Override
public void onSuccess(QuerySnapshot documentSnapshots) {
// ...
// Get the last visible document
DocumentSnapshot lastVisible = documentSnapshots.getDocuments()
.get(documentSnapshots.size() -1);
// Construct a new query starting at this document,
// get the next 25 cities.
Query next = db.collection("cities")
.orderBy("population")
.startAfter(lastVisible)
.limit(25);
// Use the query for pagination
// ...
}
});
怎么办？文档没有太多细节。
How to do? Documentation has not too many details.
PS：用户滚动时我需要使用回收站视图（不是列表视图）。谢谢
PS: I need with recycler view (not list view) when user scrolls. Thanks
推荐答案
正如官方文档，解决此问题的关键是使用 startAfter（）方法。因此，您可以通过将查询游标与 limit（）方法相结合来对查询进行分页。您将能够将批处理中的最后一个文档用作下一批的游标的开头。
As it is mentioned in the official documentation, the key for solving this problem is to use the startAfter() method. So you can paginate queries by combining query cursors with the limit() method. You'll be able to use the last document in a batch as the start of a cursor for the next batch.
要解决此分页问题，请参阅我的答案这 发布 ，我已逐步解释了如何以较小的块从Cloud Firestore数据库加载数据并将其显示在 ListView 点击按钮。
To solve this pagination problem, please see my answer from this post, in which I have explained step by step, how you can load data from a Cloud Firestore database in smaller chunks and display it in a ListView on button click.
解决方案：
从您那里获取数据Firestore数据库并以 RecyclerView 中的较小块显示，请按照以下步骤操作。
To get the data from your Firestore database and display it in smaller chunks in a RecyclerView, please follow the steps below.
让我们采取以上措施我使用过产品的例子。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 。
Let's take the above example in which I have used products. You can use products, cities or whatever you want. The principles are the same. Assuming that you want to load more products when user scrolls, I'll use RecyclerView.OnScrollListener.
让我们来定义首先是 RecyclerView 并设置布局管理器：
Let's define first the RecyclerView and set the layout manager:
RecyclerView recyclerView = findViewById(R.id.recycler_view);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
我们假设我们的数据库结构如下所示：
Let's assume we have a database structure that look like this:
Firestore-root
|
--- products (collection)
|
--- productId (document)
|
--- productName: "Product Name"
并且模型类看起来像这样：
And a model class that looks like this:
public class ProductModel {
private String productName;
public ProductModel() {}
public ProductModel(String productName) {this.productName = productName;}
public String getProductName() {return productName;}
}
这是适配器类的样子：
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 布局只包含一个视图， TextView 。
The item_product layout contains only one view, a TextView.
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/text_view"
android:textSize="25sp"/>
这就是持有人类的外观：
And this is the how the holder class should look like:
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，我们将限制定义为全局变量，设置为 15 。
Now, let's define a limit as a global variable and set it to 15.
private int limit = 15;
现在让我们使用这个限制来定义查询：
Let's define now the query using this limit:
FirebaseFirestore rootRef = FirebaseFirestore.getInstance();
CollectionReference productsRef = rootRef.collection("products");
Query firstQuery = productsRef.orderBy("productName", Query.Direction.ASCENDING).limit(limit);
以下代码也适用于您的情况：
Here is the code that also does the magic in your case:
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，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：
In which lastVisible is a DocumentSnapshot object which represents the last visibile item from the query. In this case, every 15'th one and it is declared as gloabl variable:
private DocumentSnapshot lastVisible;
isScrolling 和 isLastItemReached 也是全局变量，声明为：
And isScrolling and isLastItemReached are also global variables and are declared as:
private boolean isScrolling = false;
private boolean isLastItemReached = false;
这篇关于如何使用Android对Firestore进行分页？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
