无法从android中的firebase读取数据 [英] Unable to read data from firebase in android

问题描述

我正在开发Android应用程序，其中 Firebase 正用于维护移动后端。我在 Firebase

  {
 用户：{
-Kh2wjxeT-w26opA0yqe：{
email：[e-mail]，
firstName：XX，
利息：{
interest：[Cricket，Table Tennis，Football] 
}，
lastName：XXX，
密码：abcd @ 1234
} 
} 
} 
  

Users.java

  @IgnoreExtraProperties 
 public class User {
 
 public String firstName; 
 public String lastName; 
 public String email; 
公共字符串密码; 
 
公共利息; 
 $ b public User（）{
 //调用DataSnapshot.getValue（User.class）所需的默认构造函数
} 
 
 public User firstName，String lastName，String email，String password，Interest interest）{
 this.firstName = firstName; 
 this.lastName = lastName; 
 this.email = email; 
 this.password = password; 
 this.interest = interest; 
 
 
 
 
 $ h2 Interest.java 
 
 
  public class Interest {
 
 public List< String>利益; 
 $ b public Interest（）{
 //调用DataSnapshot.getValue（User.class）所需的默认构造函数
} 
 
 public Interest（List< ; String>兴趣）{
 this.interests = interest; 
 
 
 
 
 $ b我已经添加了 addValueEventListener 在子节点用户这样
  mDatabase.child（users）。addValueEventListener（new ValueEventListener（）{
 @Override 
 public void onDataChange（DataSnapshot dataSnapshot）{
 for（DataSnapshot noteDataSnapshot：dataSnapshot.getChildren（））{
 User user = dataSnapshot.getValue（User .class）; 
 Log.d（Scheduled，user.firstName + user.lastName + user.interest.interests.toString（））; 
} 
} 
 
 @Override 
 public void onCancelled（DatabaseError error）{
 //无法读取值
} 
}）; 
  
它正在读取正确的数据 Firebase  Users  java对象中的数据，所以当我无法访问值时。我不知道我在这里做了什么错误。 
 $ b 
 
 
 Log.d（Scheduled，user.firstName + user.lastName + user.interest.interests.toString（））;  / p> 
 
 
 
解决方案
为了显示数据，您需要像这样更改代码：
  mDatabase.child（users）。child（userId）.addValueEventListener（new ValueEventListener（）{
 @Override 
 public void onDataChange（DataSnapshot dataSnapshot）{
 String firstName = dataSnapshot.child（firstName）.getValue（String.class）; 
 Log.d（Scheduled，firstName）; 
 
 $ b @Override 
 public void onCancelled（DatabaseError error）{
 //无法读取值
} 
}）; 
  
其中 userId 是生成的唯一ID由 push（）方法。
 
I am working on android app where Firebase is being used for maintaining mobile back end. I have database in this format on Firebase
{
  "users" : {
    "-Kh2wjxeT-w26opA0yqe" : {
      "email" : "[e-mail]",
      "firstName" : "XX",
      "interest" : {
        "interests" : [ "Cricket", "Table Tennis", "Football" ]
      },
      "lastName" : "XXX",
      "password" : "abcd@1234"
    }
  }
}


Users.java

@IgnoreExtraProperties
public class User {

    public String firstName;
    public String lastName;
    public String email;
    public String password;

    public Interest interest;

    public User() {
        // Default constructor required for calls to DataSnapshot.getValue(User.class)
    }

    public User(String firstName, String lastName, String email, String password, Interest interest) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
        this.password = password;
        this.interest = interest;
    }
}


Interest.java

public class Interest {

    public List<String> interests;

    public Interest() {
        // Default constructor required for calls to DataSnapshot.getValue(User.class)
    }

    public Interest(List<String> interests) {
        this.interests = interests;
    }
}
I have added addValueEventListener on child "users" in this way 
mDatabase.child("users").addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot noteDataSnapshot : dataSnapshot.getChildren()) {
            User user = dataSnapshot.getValue(User.class);
            Log.d("Scheduled", user.firstName + user.lastName + user.interest.interests.toString());
        }
    }

    @Override
    public void onCancelled(DatabaseError error) {
        // Failed to read value
    }
});
It is fetching correct data what I have on Firebase but it is not mapping data in Users java object so when I am unable to access values. I am not sure what mistake I am doing here. 

  
Log.d("Scheduled", user.firstName + user.lastName + user.interest.interests.toString());

解决方案
In order to display the data, you need change your code like this:
mDatabase.child("users").child(userId).addValueEventListener(new ValueEventListener() { 
    @Override 
    public void onDataChange(DataSnapshot dataSnapshot) { 
        String firstName = dataSnapshot.child("firstName").getValue(String.class); 
        Log.d("Scheduled", firstName); 
    } 

    @Override 
    public void onCancelled(DatabaseError error) { 
    // Failed to read value 
    } 
});   
In which userId is the unique id generated by the push() method.

                        
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