如何使用Kotlin将数据添加到android上的firebase实时数据库？

dependencies {
    // Firebase Realtime Database
    implementation 'com.google.firebase:firebase-database-ktx:20.0.2'
}

dependencies {
    // Firebase Realtime Database
    implementation 'com.google.firebase:firebase-database-ktx:20.0.2'

    // Firebase Gradle plugin
    implementation 'com.google.firebase:firebase-analytics-ktx:18.0.2'
}

import com.google.firebase.database.FirebaseDatabase

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // 初始化Firebase
        FirebaseDatabase.getInstance().setPersistenceEnabled(true)
    }
}

import com.google.firebase.database.FirebaseDatabase

// 获取Firebase数据库的引用
val database = FirebaseDatabase.getInstance().reference

// 添加数据
val userId = "user1"
val username = "John Doe"
val userRef = database.child("users").child(userId)
userRef.child("username").setValue(username)