Kotlin中Firebase Realtime Database未解析引用等错误求助

在开发Kotlin Android项目时，使用Firebase Realtime Database遇到以下报错：在RegisterActivity中声明DatabaseReference的代码行提示“Unresolved reference: DatabaseReference”和“Expecting member declaration”错误。已尝试Stack Overflow相关解决方案，也重新连接了Firebase项目，但问题仍未解决。

报错代码 #

package com.example.movietime

import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import com.example.movietime.databinding.ActivityRegisterBinding
import com.google.firebase.ktx.Firebase

class RegisterActivity : AppCompatActivity() {

    DatabaseReference database = FirebaseDatabase.getInstance().getReference(); // also here with all sentence
    // binding
    private lateinit var binding: ActivityRegisterBinding


    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)
        binding = ActivityRegisterBinding.inflate(layoutInflater)
        setContentView(binding.root)


        // move  to login after click
        binding.submitButton.setOnClickListener {
            startActivity(Intent(this, LoginActiivty::class.java))
        }
    }
}

App模块Gradle配置 #

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

android {
    namespace 'com.example.movietime'
    compileSdk 33

    defaultConfig {
        applicationId "com.example.movietime"
        minSdk 21
        targetSdk 33
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
    buildFeatures {
        viewBinding true
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }
}

dependencies {

    implementation 'com.google.firebase:firebase-database-ktx'
    implementation 'androidx.core:core-ktx:1.9.0'
    implementation 'androidx.appcompat:appcompat:1.5.1'
    implementation 'com.google.android.material:material:1.7.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.4'
    implementation platform('com.google.firebase:firebase-bom:30.0.1')
    implementation 'com.google.firebase:firebase-analytics-ktx'
    implementation 'com.google.firebase:firebase-auth-ktx'
    implementation 'com.google.firebase:firebase-firestore-ktx'
    implementation 'com.google.firebase:firebase-firestore'
    implementation platform('com.google.firebase:firebase-bom:31.0.2')



    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'

}

项目级Gradle配置 #

buildscript {
    repositories {
        // Check that you have the following line (if not, add it):
        google()  // Google's Maven repository

    }
    dependencies {
        classpath 'com.android.tools.build:gradle:7.3.1'
        classpath 'com.google.gms:google-services:4.3.14'

    }
}
// Top-level build file where you can add configuration options common to all sub-projects/modules.
plugins {
    id 'com.android.application' version '7.3.1' apply false
    id 'com.android.library' version '7.3.1' apply false
    id 'org.jetbrains.kotlin.android' version '1.7.20' apply false
}

解决建议 #

• 补全必要导入：代码中未导入DatabaseReference和Firebase数据库相关类，需在文件顶部添加：

  import com.google.firebase.database.DatabaseReference
  import com.google.firebase.database.ktx.database
  

• 修正Kotlin变量声明语法：原代码使用Java风格的变量声明，不符合Kotlin语法。可改为：

  private lateinit var database: DatabaseReference
  

  或直接初始化：

  private val database = Firebase.database.reference
  

• 清理Gradle依赖冲突：App模块中重复引入了两个不同版本的Firebase BOM（30.0.1和31.0.2），需删除其中一个，保留最新版本的BOM确保依赖统一。建议删除implementation platform('com.google.firebase:firebase-bom:30.0.1')这一行。

• 同步并重建项目：修改依赖后点击Android Studio右上角「Sync Now」同步Gradle，再执行「Build -> Clean Project」和「Build -> Rebuild Project」，确保依赖正确加载。

• 修正类名拼写错误：代码中LoginActiivty多了一个字母i，应改为LoginActivity，避免后续跳转功能异常。

内容的提问来源于stack exchange，提问作者Adir