错误：无法解析'：app @ debug / compileClasspath'的依赖关系：无法解析com.google.firebase：firebase-database：19.2.1

Question

应用插件：“ com.android.application” 应用插件：“ com.google.gms.google-services”

android { 编译版本28 buildToolsVersion“ 29.0.3”

defaultConfig {
    applicationId "com.example.firebaseapp"
    minSdkVersion 21
    targetSdkVersion 28
    versionCode 1
    versionName "1.0"

    testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
}

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

}

依赖项{ 实现fileTree（dir：'libs'，包括：['* .jar']）

implementation 'androidx.appcompat:appcompat:1.1.0'
implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
implementation 'com.google.firebase:firebase-database:19.2.1'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'androidx.test.ext:junit:1.1.1'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'

}