java - 如何从Android（Java）中的Firestore读取嵌套对象值及其键

Question

我正在尝试从嵌套对象中读取值以及 android 中的键，但我无法根据我的要求找到任何解决方案。（我是 Firestore 和 android 开发的新手）

我尝试了 foreach 循环，但它显示错误- foreach 不适用于类型'java.util.Map'： -

for(DocumentSnapshot ds: document.getData())

所以然后我尝试了这个： -

Map<String, Object> myMap = (Map<String, Object>) document.getData();
String name = ""; //don't know how to get key i.e(clamp,gear) as i can't pass all of them.
String url = (String) myMap.get("url");//url returns null

这是我的代码：-

FirebaseFirestore db = FirebaseFirestore.getInstance();
DocumentReference docRef = db.collection("categoryType").document("Hardware");
docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
            @Override
            public void onComplete(@NonNull Task<DocumentSnapshot> task) {
                if (task.isSuccessful()) {
                    DocumentSnapshot document = task.getResult();
                    if (document.exists()) {
                        Log.d(TAG, "DocumentSnapshot data: " + document.getData());//see log below
                        Map<String, Object> myMap = (Map<String, Object>) document.getData();
                        String name = "";
                        String url = (String) myMap.get("url");
                        ItemCategory category = new ItemCategory(name,url);
                        itemCategoryList.add(category);
                    } else {
                        Log.d(TAG, "No such document");
                    }
                } else {
                    Log.d(TAG, "get failed with ", task.getException());
                }
                itemCategoryAdapter.notifyDataSetChanged();
            }
        });

Log.d 打印：-
{Hammer={url=https://someURL}, Nail={url=https://someURL}, Shovel={url=https://someURL}}

所以简而言之，我想要的是：-
name = "Hammer"
url = "someUrl",

名称 = “钉子”
url = “someurl”

标签： javaandroidfirebasegoogle-cloud-firestore

Answer 1

首先，您必须获取 Clamp 映射，然后使用它来获取其 url 属性。这是伪代码，不是完整代码，但说明了您需要做什么。为简洁起见，缺少地图上的泛型：

// get the document data map from the snapshot
Map data = snapshot.getData();
// get the Clamp field, which is an object field, so it will arrive as a Map
Map clamp = (Map) data.get("Clamp");
// get the String value of the url property on the object
String url = (String) clamp.get("url");