dataSnapshot具有对象，但getValue()将返回null [英] dataSnapshot has the object but getValue() will return null

问题描述

所以我现在正为这个问题苦苦挣扎约三个小时.
我有这个用户类别

So I'm struggling with this issue for about three hours now.
I have this user class

public class User {
private String user_id;
private String userName;
private long phoneNumber;

public User() {
}

public User(String user_id, String userName, long phoneNumber) {
    this.user_id = user_id;
    this.userName = userName;
    this.phoneNumber = phoneNumber;
}

我想从Firebase数据库中获取此类的某些实例，我正在使用以下代码来做到这一点:
数据库参考；

And I want to fetch some instances of this class from Firebase Database I am using this code to do so:
database reference;

User currentUser;
DatabaseReference database = FirebaseDatabase.getInstance().getReference(); 
DatabaseReference usersRef = database.child("users");

查询代码:

Query query = usersRef.orderByChild("user_id").equalTo(user_id);
                query.addListenerForSingleValueEvent (new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                         currentUser = dataSnapshot.getValue(User.class);
}

有趣的是:这段代码实际上只工作过一次，但是我猜想我做了一些更改，现在getValue()返回null.
这是我在firebase中的数据库

当我调试应用程序时，dataSnapshot实际上包含了我要查找的对象

但currentUser将是其所有字段为null的对象；

有任何想法吗?我已经很沮丧了:( 预先感谢！

Funny thing: this code actually worked once but I made some changes I guess, and now the getValue() returns null;
this is my database in firebase

and when I debug the app the dataSnapshot actually contains the object I am looking for

but the currentUser will be an object with all its fields null;

any ideas? I'm getting really frustrated already :( Thanks in advance!

推荐答案

您需要遍历dataSnapshot.getChildren( ...例如

You need to iterate over dataSnapshot.getChildren(...for example

                for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
                    User user = childSnapshot.getValue(User.class);
                 }

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