尝试以下查询以获取单个用户的多个文档-

db.collection("images")
        .whereEqualTo("user_id", FirebaseAuth.getInstance().getCurrentUser().getUid())
        .get()
        .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
            @Override
            public void onComplete(@NonNull Task<QuerySnapshot> task) {
                if (task.isSuccessful()) {  
                    for (QueryDocumentSnapshot document : task.getResult()) {
                           Item item = new Item();
                           item.setItemName(document.getString("name"));
                           item.setItemPrice(document.getString("price"));
                           item.setItemDescription(document.getString("description"));
                           item.setItemImage(document.getString("image"));
                           itemList.add(item);
                    }
            shoeAdapter = new ShoeAdapter(MainActivity.this, itemList);
                    recyclerView.setAdapter(shoeAdapter);
                    shoeAdapter.notifyDataSetChanged();
                } else {
                    Log.d(TAG, "Error getting documents: ", task.getException());
                }
            }
        });

检查文档中是否有更多此类查询-https://firebase.google.com/docs/firestore/query-data/queries

不需要分别获取每个字段的值。您可以直接将Realtime Database中的子对象Map到Item类型的对象中。为了能够做到这一点，您必须如下更改类的声明：

public class Item {
    private String name;
    private String price;
    private String description;
    private String image;
    private String userId;

    public Item(String name, String price, String description, String image, String userId) {
        this.name = name;
        this.price = price;
        this.description = description;
        this.image = image;
        this.userId = userId;

    }
    public Item(){

    }
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPrice() {
        return price;
    }

    public void setPrice(String price) {
        this.price = price;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public String getImage() {
        return image;
    }

    public void setImage(String image) {
        this.image = image;
    }

    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }
}

为什么？因为类中字段的名称应该命名数据库中存在的名称。
现在，为了获得与登录用户相对应的图像，您必须初始化列表、适配器和RecyclerView，并创建如下所示的查询：

itemList = new ArrayList<>();
shoeAdapter = new ShoeAdapter(MainActivity.this, itemList);
recyclerView.setAdapter(shoeAdapter);

String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
FirebaseFirestore db = FirebaseFirestore.getInstance();
Query queryByUserId = db.collection("images").whereEqualTo("userId", uid);
queryByUserId.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
    @Override
    public void onComplete(@NonNull Task<QuerySnapshot> task) {
        if (task.isSuccessful()) {
            for (QueryDocumentSnapshot document : task.getResult()) {
                if (document != null) {
                    Item item = document.toObject(Item.class);
                    itemList.add(item);
                    Log.d("TAG", item.getName());
                }
            }
            shoeAdapter.notifyDataSetChanged();
        } else {
            Log.d("TAG", task.getException().getMessage()); //Never ignore potential errors!
        }
    }
});

我所做的更改：
1.不需要使用while循环，只需要检查空值。
1.我已经在异步操作之外添加了与UI相关的声明。一旦获取Item对象的操作完成，我们只通知适配器有关的更改。
1.始终处理错误。