firebase的实时数据库没有显示数据(显示null)

Question

应用程序正在运行fine...just数据未显示...我已经添加了用户电子邮件在登录后显示，并且在登录活动中我已经添加了

FirebaseDatabase.getInstance().getReference().child("aj").child("name").setValue("aditya");

但在实时数据库中，数据不会显示，以防..i在尝试后等待半个小时，所有things..network也是好的。数据库中的数据库picture of database规则之前是

{
  "rules": {
    ".read": "now < 1625337000000",  // 2021-7-4
    ".write": "now < 1625337000000",  // 2021-7-4
  }
}

我读到这应该是真的，所以现在rules

并且added_firebase在初始化时给出了错误

 FirebaseDatabase mDatabase;
mDatabase = FirebaseDatabase.getInstance().getReference();

android studio想要像这样改变mDataBase的类型，现在不给出错误

DatabaseReference mDatabase;
mDatabase = FirebaseDatabase.getInstance().getReference();

app gradle文件

plugins {
    id 'com.android.application'
    id 'com.google.gms.google-services'
}

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.3"

    defaultConfig {
        applicationId "com.example.firebase0"
        minSdkVersion 16
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

dependencies {

    implementation 'androidx.appcompat:appcompat:1.3.0'
    implementation 'com.google.android.material:material:1.3.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    implementation 'com.google.firebase:firebase-auth:21.0.1'
    implementation 'com.google.firebase:firebase-database:20.0.0'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
}

MainActivity.java //不适用于单个子代，即FirebaseDatabase.getInstance().getReference().child("aj").child("name").setValue("aditya")；，也不适用于map .searched it...tried隐名模式，不同浏览器，数据库中devices...still为空

package com.example.firebase0;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import com.google.android.gms.tasks.OnFailureListener;
import com.google.android.gms.tasks.OnSuccessListener;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;

import java.util.HashMap;

public class MainActivity extends AppCompatActivity {

    private Button logout;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        logout= findViewById(R.id.logout_button);
//        FirebaseDatabase  mDatabase;
//        mDatabase = FirebaseDatabase.getInstance().getReference();

        logout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FirebaseAuth.getInstance().signOut();
                Toast.makeText(MainActivity.this,"logged out successfully",Toast.LENGTH_SHORT).show();
                startActivity(new Intent(MainActivity.this, StartActivity.class));
            }
        });

        //FirebaseDatabase.getInstance().getReference().child("aj").child("name").setValue("aditya");
        //yha aj branch ka name child hai uski value aditya
        // agr ek branch ke ek se jada child bnane to hashmap
//        DatabaseReference mDatabase;
//        mDatabase = FirebaseDatabase.getInstance().getReference();



        HashMap<String , Object> map = new HashMap<>();
        map.put("name","aj");
        map.put("sirname","jain");
        map.put("desh","bharat");

        FirebaseDatabase.getInstance().getReference().child("aj_database").child("multiple_children").setValue(map).addOnSuccessListener(new OnSuccessListener<Void>() {
            @Override
            public void onSuccess(Void aVoid) {
                Toast.makeText(MainActivity.this,"Posted are Success",Toast.LENGTH_SHORT).show();
            }
        })
                .addOnFailureListener(new OnFailureListener() {
                    @Override
                    public void onFailure(@NonNull Exception e) {
                        Toast.makeText(MainActivity.this,"Posted are Failed\n"+e,Toast.LENGTH_SHORT).show();
                    }
                });;
    }
}

Answer 1

添加onSuccessListener以了解写入是否已完成。

 HashMap<String , Object> map = new HashMap<>();
        map.put("name","aj");
        map.put("sirname","jain");
        map.put("desh","bharat");

mDatabase.child("aj database").child("multiple children").setValue(map)
        .addOnSuccessListener(new OnSuccessListener<Void>() {
            @Override
            public void onSuccess(Void aVoid) {
                // Write was successful!
                // ...
            }
        })
        .addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                // Write failed
                // ...
            }
        });

Answer 2

FirebaseDatabase.getInstance().getReference().child("aj database").child("multiple children").setValue(map);

有关follow this的更多信息

Answer 3

public class User {  // Create user-class 
    public String name;
    public String surname;
    public String desh;
    
    public User {}
    
    public User(String name, String surname, String desh) {
        this.name = name;
        this.surname = surname;
        this.desh = desh;
    }
    
    @Exclude
    public Map<String, Object> toMap() {
        HashMap<String, Object> result = new HashMap<>();
        result.put("name", name);
        result.put("surname", surname);
        result.put("desh", desh);
        return result;
    }
    
}

public class MainActivity extends AppCompatActivity {

    // ...
    FirebaseDatabase mDatabase;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        mDatabase = FirebaseDatabase.getInstance().getReference();
        // ...

        writeNewUser("aj", "jain", "bharat");

    }
    
    // method to save new user
    private void writeNewUser(String name, String surname, String desh) {
        String userKey = mDatabase.child("users").push().getKey(); // a unique user key
        User user = new User(name, surname, desh);
        Map<String, Object> userValues = user.toMap();
        mDatabase.updateChildren(new HashMap<String, Object>().put("/users/" + userKey, userValues));
    }
    
}