2)Dialog
Code:
package srm.it.dialog
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Toast
import androidx.appcompat.app.AlertDialog
import kotlinx.android.synthetic.main.activity_main.
class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        button.setOnClickListener {
            var mydialog=AlertDialog.Builder(this)
            mydialog.setTitle("Hello")
            mydialog.setMessage("do you want to exit ?...")
            mydialog.setPositiveButton("Yes"){dialog,which->
                Toast.makeText(this,"you click yes",Toast.LENGTH_LONG).show()
            }
            mydialog.setNegativeButton("No"){dialog,which->
                Toast.makeText(this,"you click No",Toast.LENGTH_LONG).show()
            }
            mydialog.setNeutralButton("cancel"){dialog,which->
                Toast.makeText(this,"you click No",Toast.LENGTH_LONG).show()
            }
            mydialog.show()
        }
    }
    override fun onBackPressed() {
        var mydialog=AlertDialog.Builder(this)
        mydialog.setTitle("Hello")
        mydialog.setMessage("do you want to exit ?...")
        mydialog.setPositiveButton("Yes"){dialog,which->
            Toast.makeText(this,"you click yes",Toast.LENGTH_LONG).show()
        }
        mydialog.setNegativeButton("No"){dialog,which->
            Toast.makeText(this,"you click No",Toast.LENGTH_LONG).show()
        }
        mydialog.setNeutralButton("cancel"){dialog,which->
            Toast.makeText(this,"you click No",Toast.LENGTH_LONG).show()
        }
        mydialog.show()
    }
}


3)Dialog fragments
Code:
.kt file code:
package com.example.dialogfragment
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import kotlinx.android.synthetic.main.activity_main.*
class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        button.setOnClickListener {
            var obj=Myclass()
            obj.show(supportFragmentManager,"tyit")
        }
    }
}
.xml file code:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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=".MainActivity">
    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Click"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
second .kt file code:
package com.example.dialogfragment
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Toast
import androidx.fragment.app.DialogFragment
import kotlinx.android.synthetic.main.mylayout.view.*
class Myclass:DialogFragment() {
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        var s=inflater.inflate(R.layout.mylayout,container)
        s.btn.setOnClickListener {
            var d=s.text.text.toString()
            Toast.makeText(context,"Welcome",Toast.LENGTH_LONG).show()
        }
        return s
    }
}
second .xml file code:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/text"
        android:hint="@string/app_name"/>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/text"
        android:id="@+id/btn"
        android:text="submit"/>
</RelativeLayout>

