无法获取 FirebaseDatabase 实例：在 FirebaseApp 内或从您的 getInstance() 调用中指定 DatabaseURL

Question

我正在学习本教程 https://www.geeksforgeeks.org/how-to-populate-recyclerview-with-firebase-data-using-firebaseui-in-android-studio/

所以我可以从我的 Firebase 数据库填充我的 Recycleview，但我的应用程序开始崩溃并且我需要指定数据库 url 的错误。

我已尝试按照以下步骤下载 google-service.json 。改变我写网址等的方式

这是我的依赖：

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

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.3"

    defaultConfig {
        applicationId "com.example.app"
        minSdkVersion 16
        targetSdkVersion 29
        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:1.2.0'
    implementation 'com.google.android.material:material:1.2.1'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    implementation 'androidx.legacy:legacy-support-v4:1.0.0'
    implementation 'androidx.recyclerview:recyclerview:1.1.0'
    implementation 'com.google.firebase:firebase-database:19.2.1'
    implementation 'com.firebaseui:firebase-ui-database:6.0.2'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
}

这是我尝试检索数据的方法：

  public View onCreateView(@NonNull LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) {
        root = inflater.inflate(R.layout.fragment_articles, container, false);
        recyclerView = root.findViewById(R.id.recyclerView);
        mbase = FirebaseDatabase.getInstance().getReference();
        FirebaseRecyclerOptions<NewsList> news
                = new FirebaseRecyclerOptions.Builder<NewsList>()
                .setQuery(mbase, NewsList.class)
                .build();
        adapter = new NewsAdapter(news);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager( new LinearLayoutManager(getActivity()));
        recyclerView.setAdapter(adapter);

这是我的数据类：

public class NewsList {
    private String title;
    private String author;

    public NewsList(String title,String author) {
        this.title = title;
        this.author =author;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }


    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }



}

我的数据库结构如下：

我也试过包括 url :

mbase = FirebaseDatabase.getInstance().getReference(url);

我在依赖项中缺少某些东西，或者我没有编写正确的代码？