Question

我需要获取模型类列表中的数据快照，但现在我得到空值。当我调试时，我发现我的模型类没有实际从我的satasnapshot和添加消息中获取数据

我正在使用的代码。

model class
package com.teamta.artiando.models;

public class MatchModel {

private String last_message;
public String last_message_sender_id;
public Object last_message_timestamp;
public Object timestamp;
public User user1;
public User user2;

public MatchModel(String last_message, String last_message_sender_id, Object last_message_timestamp, Object timestamp, User user1, User user2) {
    this.last_message = last_message;
    this.last_message_sender_id = last_message_sender_id;
    this.last_message_timestamp = last_message_timestamp;
    this.timestamp = timestamp;
    this.user1 = user1;
    this.user2 = user2;


}
public MatchModel(){

}

public String getLast_message() {
    return last_message;
}

public void setLast_message(String last_message) {
    this.last_message = last_message;
}

public String getLast_message_sender_id() {
    return last_message_sender_id;
}

public void setLast_message_sender_id(String last_message_sender_id) {
    this.last_message_sender_id = last_message_sender_id;
}

public Object getLast_message_timestamp() {
    return last_message_timestamp;
}

public void setLast_message_timestamp(Object last_message_timestamp) {
    this.last_message_timestamp = last_message_timestamp;
}

public Object getTimestamp() {
    return timestamp;
}

public void setTimestamp(Object timestamp) {
    this.timestamp = timestamp;
}

public User getUser1() {
    return user1;
}

public void setUser1(User user1) {
    this.user1 = user1;
}

public User getUser2() {
    return user2;
}

public void setUser2(User user2) {
    this.user2 = user2;
}

public static class User {

    private String name;
    public String profilepic_url;
    public String userId;

    public User(String name, String profilepic_url, String userId) {
        this.name = name;
        this.profilepic_url= profilepic_url;
        this.userId =userId;
    }

    public String getName() {
        return name;
    }

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

    public String getProfilepic_url() {
        return profilepic_url;
    }

    public void setProfilepic_url(String profilepic_url) {
        this.profilepic_url = profilepic_url;
    }

    public String getUserId() {
        return userId;
    }

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

}

}

在我的经理班上我使用

 private  ValueEventListener userCalueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {

        MatchModel messages = dataSnapshot.getValue(MatchModel.class);
        name.add(messages);

    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        Log.d("year", "DatabaseError: "+databaseError);
    }
};

这是我的查询

  public void observeUserdata() {        FirebaseDatabase.getInstance().getReference().child("matches").orderByChild(userId).equalTo(true).addValueEventListener(userCalueEventListener);
}

我的firbase看起来像

matches
  |
  |-kwerrwuw8iaajasd    // i have 30 key like this key in the matches in this node
          |- Kweyatsgdywywyww
          |- last_message
          |- last_senderuserid
          |- timestamp
          |-user1
          |    |- name
          |    |- profile_pic
          |    |- user_id
          |-user2
          |    |- name
          |    |- profile_pic
          |    |- user_id
          |- Kweyatsgdywywyww

Answer 1

你需要在onDataChange（）方法中启动一个循环并逐个访问你的数据并放入你的列表，然后你就可以得到消息列表。

 public void onDataChange(DataSnapshot dataSnapshot) {
     for(DataSnapshot data: dataSnapshot.getChildren()){

          yourClass obj=data.getValue(yourClass.class);
          yourList.add(obj);
      }

 }

Answer 2

您收到null，因为您使用了错误的DatabaseReference。

FirebaseDatabase.getInstance().getReference() 
    .child("matches")
    .orderByChild(userId)
    .equalTo(true).addValueEventListener(userCalueEventListener);

正如我在您的数据库结构中看到的那样，您正在尝试按用户对象对子项进行排序，而您无法以这种方式进行查询。您可以做的是在timestamp后查询，matches是FirebaseDatabase.getInstance().getReference() .child("matches") .orderByChild(userId) .equalTo(true).addValueEventListener(userCalueEventListener);节点的直接子节点。您的查询应如下所示：

return holder

Answer 3

您需要在所有模型类中添加一个空构造函数，如果它们是模型类中的内部类，则还需要向该类添加一个空构造函数

当我使用模型类从firebase获取数据时获取空值

3 个答案: