Question

我正在使用Firebase作为后端服务器开发基于Android的应用程序。我已按以下方式设计了应用程序的结构：

Project Name
|_ Products
|_ groups
   |_ 1BME
      |_ members
         |_ -K4usWDhtiw4U
             |_ Custom Object
         |_ -K4uscDHwYsXHs
             |_ Custom Object

自定义对象是：

package com.app.shubhamjhunjhunwala.heritagecompanion_students;

import android.net.Uri;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;

/**
 * Created by shubham on 23/01/17.
 */

public class UserDetails {

    UserDetails() {}

    public String name;
    public String email;
    public String password;
    public String phone;
    public String roll;
    public String department;
    public String year;
    public String section;
    public String dpDownloadUri;

    public UserDetails(String name, String email, String password, String phone, String roll, String department, String year, String section, String dpDownloadUri) {
        this.name = name;
        this.email = email;
        this.password = password;
        this.phone = phone;
        this.roll = roll;
        this.department = department;
        this.year = year;
        this.section = section;
        this.dpDownloadUri = dpDownloadUri;
    }

    public String getName() {
        return name;
    }

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

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    public String getRoll() {
        return roll;
    }

    public void setRoll(String roll) {
        this.roll = roll;
    }

    public String getDepartment() {
        return department;
    }

    public void setDepartment(String department) {
        this.department = department;
    }

    public String getYear() {
        return year;
    }

    public void setYear(String year) {
        this.year = year;
    }

    public String getSection() {
        return section;
    }

    public void setSection(String section) {
        this.section = section;
    }

    public String getDpDownloadUri() {
        return dpDownloadUri;
    }

    public void setDpDownloadUri(String dpDownloadUri) {
        this.dpDownloadUri = dpDownloadUri;
    }
}

我的目的是在“群组”子项下的1BME下的成员子项下获取用户详细信息。所以为此，我在程序中使用了以下代码：

mDatabase = FirebaseDatabase.getInstance();
mGroupMembersDatabaseReference = mDatabase.getReference().child("groups").child(groupRoll).child("members");

mGroupMembersDatabaseReference.addChildEventListener(new ChildEventListener() {
                        @Override
                        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                            UserDetails users = dataSnapshot.getValue(UserDetails.class);

                            Toast.makeText(GroupChatActivity.this, users.getRoll(), Toast.LENGTH_SHORT).show();

                            if (!users.getRoll().equals(senderRoll)) {

                                Toast.makeText(GroupChatActivity.this, users.getName(), Toast.LENGTH_SHORT).show();

                                mRecieverDatabaseReference = mRecieverDatabaseReference.child(users.getRoll()).child("groups").child(groupRoll);

                                Query query1 = mRecieverDatabaseReference.orderByChild("roll").equalTo(groupRoll);
                                query1.addListenerForSingleValueEvent(new ValueEventListener() {
                                    @Override
                                    public void onDataChange(DataSnapshot dataSnapshot) {
                                        for (DataSnapshot dataSnapshot1 : dataSnapshot.getChildren()) {
                                            dataSnapshot1.getRef().child("state").setValue("unread");
                                            dataSnapshot1.getRef().child("timeID").setValue(timeID);
                                        }
                                    }

                                    @Override
                                    public void onCancelled(DatabaseError databaseError) {

                                    }
                                });

                                Messages message = new Messages(messageText, time, senderRoll, name, chatName, groupRoll, mState, messageType, "");
                                mRecieverDatabaseReference.push().setValue(message);

                                mRecieverDatabaseReference = mDatabase.getReference().child("chats");
                            }
                        }

                        @Override
                        public void onChildChanged(DataSnapshot dataSnapshot, String s) {

                        }

                        @Override
                        public void onChildRemoved(DataSnapshot dataSnapshot) {

                        }

                        @Override
                        public void onChildMoved(DataSnapshot dataSnapshot, String s) {

                        }

                        @Override
                        public void onCancelled(DatabaseError databaseError) {

                        }
                    });

在此代码字符串groupRoll = "1BME"

中

但是当我运行此代码并对其进行调试时，我发现它永远不会进入onChildAdded()。所以请帮助我。该应用程序因此没有向前发展。

谢谢。

Answer 1

首先，您的DatabaseReference是错误的。要从会员处获取数据，请使用以下代码：

mGroupMembersDatabaseReference = mDatabase.getReference().child("groups").child(groupRoll).child("members").child(memberId);

其中memberId是push()方法生成的唯一ID。

其次，您不需要使用addListenerForSingleValueEvent来更改值。在setValue()上使用DataSnapshot方法是错误的。您可以直接在setValue()上使用reference。希望它有所帮助。

Answer 2

试试这个

for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
    UserDetails users = snapshot.getValue(UserDetails.class);
    //...
}

代码不会导致Firebase数据库子事件侦听器错误

2 个答案: