如何在Android RecyclerView中结合Firestore实现按类别汇总金额

1. 创建汇总数据实体类 #

首先需要一个新的实体类来存储类别-总金额的对应关系，替代原来的Expenses实体用于RecyclerView展示：

public class CategoryTotal {
    private String category;
    private double totalAmount;

    // Firestore序列化需要空构造方法
    public CategoryTotal() {}

    public CategoryTotal(String category, double totalAmount) {
        this.category = category;
        this.totalAmount = totalAmount;
    }

    // Getter & Setter
    public String getCategory() { return category; }
    public void setCategory(String category) { this.category = category; }
    public double getTotalAmount() { return totalAmount; }
    public void setTotalAmount(double totalAmount) { this.totalAmount = totalAmount; }
}

2. 实现数据汇总逻辑 #

在Firestore查询成功后，遍历拿到的Expenses列表，用HashMap按类别累加金额，再转成CategoryTotal列表：

// 假设你的Firestore查询代码
db.collection("Expenses")
        .whereEqualTo("email", targetEmail)
        .whereGreaterThanOrEqualTo("timestamp", startTime)
        .whereLessThanOrEqualTo("timestamp", endTime)
        .get()
        .addOnSuccessListener(querySnapshot -> {
            List<Expenses> expenseList = querySnapshot.toObjects(Expenses.class);
            
            // 按类别汇总金额
            HashMap<String, Double> categorySumMap = new HashMap<>();
            for (Expenses expense : expenseList) {
                String category = expense.getCategory();
                double amount = expense.getAmount();
                // 累加金额，无该类别则默认0
                categorySumMap.put(category, categorySumMap.getOrDefault(category, 0.0) + amount);
            }
            
            // 转换为RecyclerView可用的列表
            List<CategoryTotal> categoryTotalList = new ArrayList<>();
            for (Map.Entry<String, Double> entry : categorySumMap.entrySet()) {
                categoryTotalList.add(new CategoryTotal(entry.getKey(), entry.getValue()));
            }
            
            // 绑定RecyclerView
            setupRecyclerView(categoryTotalList);
        })
        .addOnFailureListener(e -> {
            // 处理查询失败逻辑
        });

3. 修改RecyclerView Adapter #

替换原Adapter的泛型为CategoryTotal，适配新的实体类：

public class CategoryTotalAdapter extends RecyclerView.Adapter<CategoryTotalAdapter.ViewHolder> {
    private List<CategoryTotal> mDataList;

    public CategoryTotalAdapter(List<CategoryTotal> dataList) {
        this.mDataList = dataList;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.item_category_total, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        CategoryTotal item = mDataList.get(position);
        holder.tvCategory.setText(item.getCategory());
        // 格式化金额为两位小数
        holder.tvTotal.setText(String.format("%.2f", item.getTotalAmount()));
    }

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

    static class ViewHolder extends RecyclerView.ViewHolder {
        TextView tvCategory, tvTotal;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            tvCategory = itemView.findViewById(R.id.tv_category);
            tvTotal = itemView.findViewById(R.id.tv_total_amount);
        }
    }
}

4. 调整RecyclerView Item布局 #

新建item_category_total.xml布局，用于展示类别和汇总后的金额：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="16dp"
    android:orientation="horizontal"
    android:justifyContent="space-between">

    <TextView
        android:id="@+id/tv_category"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="16sp"
        android:textStyle="bold"/>

    <TextView
        android:id="@+id/tv_total_amount"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="16sp"/>

</LinearLayout>

5. 绑定RecyclerView的辅助方法 #

添加初始化RecyclerView的方法：

private void setupRecyclerView(List<CategoryTotal> dataList) {
    RecyclerView recyclerView = findViewById(R.id.your_recyclerview_id);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));
    recyclerView.setAdapter(new CategoryTotalAdapter(dataList));
}

内容的提问来源于stack exchange，提问作者Dulitha Bandaranayake