Recyclerview not displaying list item but gray background and text "android...RecyclerView" - api

Question

i am a new to Kotlin Android development,i added recycler view to my project and then move the icon to the layout according to the tutorial i was watching but it not displaying anything except gray background and this black text "andriod...recycler" instead of displaying the list items samples as in the tutorial
i suspect it the api level, the android studio version is 3.1
it on Api28, here is the activity_hobbies.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v7.widget.RecyclerView
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
this is HobbiesActivity.tk
package org.blessedmedia.www.kotlinapp
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
class HobbiesActivity : AppCompatActivity(){
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_hobbies)
}
}
if you need any more file to provide solution.kindly comment