Populate listview using kotlin and firebase listview adapter

main.xml

<?xml version="1.0" encoding="utf-8"?>

<android.support.constraint.ConstraintLayout 

xmlns:android="http://schemas.android.com/apk/res/android"  

  xmlns:app="http://schemas.android.com/apk/res-auto"   

 xmlns:tools="http://schemas.android.com/tools"    

android:layout_width="match_parent"    

android:layout_height="match_parent"   

 tools:context="com.andela.smithnwokocha.firebaselistview.MainActivity">
    <EditText        

        android:id="@+id/editText"     

       android:layout_width="match_parent"      

       android:layout_height="wrap_content"      

      android:layout_marginBottom="5dp"        

      android:layout_marginEnd="90dp"       

       android:layout_marginLeft="16dp"      

       android:drawableLeft="@drawable/ic_mood"     

        android:ems="10"        

       android:hint="Type Your Message"     

     android:inputType="textPersonName"        

     app:layout_constraintBottom_toBottomOf="parent"      

      app:layout_constraintEnd_toEndOf="parent"       

      app:layout_constraintLeft_toLeftOf="parent" />
    <Button        

       android:id="@+id/button2"     

      android:layout_width="wrap_content" 

       android:layout_height="wrap_content"

        android:layout_marginBottom="2dp" 

       android:layout_marginStart="2dp" 

       android:text="Send" 

       app:layout_constraintBottom_toBottomOf="parent"

        app:layout_constraintRight_toRightOf="parent" 

       app:layout_constraintStart_toEndOf="@+id/editText" />
    <ListView 

       android:id="@+id/list"

        android:layout_width="368dp"

        android:layout_height="445dp"

        android:layout_marginBottom="8dp"

        android:layout_marginEnd="8dp" 

       android:layout_marginStart="8dp"

        app:layout_constraintBottom_toTopOf="@+id/editText"

        app:layout_constraintEnd_toEndOf="parent"

        app:layout_constraintStart_toStartOf="parent" />

     </android.support.constraint.ConstraintLayout>

row.xml

<?xml version="1.0" encoding="utf-8"?>

<android.support.constraint.ConstraintLayout

    xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    android:layout_width="match_parent"

    android:layout_height="match_parent">
    <TextView

        android:id="@+id/textView"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_marginLeft="16dp"

        android:layout_marginTop="16dp"

        android:text="TextView"

        android:textColor="@android:color/black"

        android:textSize="18sp" 

       android:textStyle="bold" 

       app:layout_constraintLeft_toLeftOf="parent"

        app:layout_constraintTop_toTopOf="parent" />

    </android.support.constraint.ConstraintLayout>

main activity

class MainActivity : AppCompatActivity() {
private val db = FirebaseDatabase.getInstance()

.getReferenceFromUrl("https://listviewtest-338e0.firebaseio.com/users")
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
       // val ref = db      val  mlist=findViewById<View>(R.id.list) as ListView
        val adapter = object : FirebaseListAdapter<String>

(this,String::class.java,R.layout.row,db)
        {
            override fun populateView(v: View?, model: String?, position: Int) {
                val text = v?.findViewById(R.id.textView) as TextView
                text.text = model
            }
        }
        mlist.adapter=adapter
    }
}