Simple Group chat app in Android studio using kotlin And firebase

MAIN ACTIVITY

package com.andela.smithnwokocha.firebaselistview

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.Button
import android.widget.EditText
import android.widget.ListView
import android.widget.TextView
import com.firebase.ui.database.FirebaseListAdapter
import com.google.firebase.database.FirebaseDatabase

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 btn=findViewById<View>(R.id.button2) as Button
        val enter=findViewById<View>(R.id.editText) as EditText
       // 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

        btn.setOnClickListener {
            val ad=enter.text.toString().trim()
                  enter.text=null                db.push().setValue(ad)


        }    }
}

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="match_parent"       

 android:layout_height="445dp"       

 android:layout_marginBottom="8dp"       

 android:layout_marginEnd="8dp"       

 android:listSelector="@android:color/transparent"       

 android:transcriptMode="alwaysScroll"       

 android:divider="@null"       

 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">    

<LinearLayout       

 android:layout_width="wrap_content"     

   android:layout_height="wrap_content"       

 android:layout_alignParentLeft="true"
        android:orientation="vertical"       

 android:paddingBottom="10dp">
    <TextView      

  android:id="@+id/textView"        

android:layout_width="wrap_content"      

  android:layout_height="wrap_content"      

  android:layout_marginTop="16dp"       

 android:maxWidth="100dp"       

 android:padding="5dp"       

 android:text="TextView"        

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

   android:textSize="18sp"       

 android:textStyle="bold" />    

</LinearLayout></android.support.constraint.ConstraintLayout>

FIREBASE UI DEPENDENCIES

implementation 'com.google.firebase:firebase-database:10.0.0'

implementation 'com.firebaseui:firebase-ui-database:0.6.2'