Custom Dialog + Interface Tutorial on Kotlin

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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="ru.skillbox.custom_dialog_interface_tutorial.MainActivity">

    <TextView
        android:id="@+id/textview_username"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_centerVertical="true"
        android:gravity="center_horizontal"
        android:text="here will be our username"
        android:textSize="30sp" />

    <TextView
        android:id="@+id/textview_password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/textview_username"
        android:layout_alignParentStart="true"
        android:gravity="center_horizontal"
        android:text="here will be our password"
        android:textSize="30sp" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/textview_password"
        android:layout_centerHorizontal="true"
        android:text="open dialog" />

</RelativeLayout>

ExampleDialog.kt

package ru.skillbox.custom_dialog_interface_tutorial

import android.app.Dialog
import android.content.Context
import android.os.Bundle
import android.view.View
import android.widget.EditText
import androidx.appcompat.app.AlertDialog
import androidx.appcompat.app.AppCompatDialogFragment


class ExampleDialog : AppCompatDialogFragment() {
    private var listener: ExampleDialogListener? = null
    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
        val inflater = requireActivity().layoutInflater
        val view: View = inflater.inflate(R.layout.layout_dialog, null)

        val editTextUsername = view.findViewById<EditText>(R.id.edit_username)
        val editTextPassword = view.findViewById<EditText>(R.id.edit_password)

        return AlertDialog.Builder(requireActivity())
            .setView(view)
            .setTitle("Login")
            .setNegativeButton("Cancel") {_, _, ->}
            .setPositiveButton("Ok") {_, _, ->
                val username = editTextUsername.text.toString()
                val password = editTextPassword.text.toString()
                listener!!.applyTexts(username, password)
            }
            .create()
    }

    override fun onAttach(context: Context) {
        super.onAttach(context)
        listener = try {
            context as ExampleDialogListener
        } catch (e: ClassCastException) {
            throw ClassCastException(
                context.toString() +
                        "must implement ExampleDialogListener"
            )
        }
    }

    interface ExampleDialogListener {
        fun applyTexts(username: String?, password: String?)
    }
}

layout_dialog.xml

<?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"
    android:padding="16dp">

    <EditText
        android:id="@+id/edit_username"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Username" />

    <EditText
        android:id="@+id/edit_password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/edit_username"
        android:layout_alignParentStart="true"
        android:hint="Password"
        android:inputType="textPassword" />

</RelativeLayout>

MainActivity.kt

package ru.skillbox.custom_dialog_interface_tutorial

import android.os.Bundle
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*


class MainActivity : AppCompatActivity(), ExampleDialog.ExampleDialogListener {
    private var textViewUsername: TextView? = null
    private var textViewPassword: TextView? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        textViewUsername = textview_username
        textViewPassword = textview_password

        //You can use the old search method
        //val button = findViewById<View>(R.id.button) as Button

        //Or use the synthetic library. Don't forget to add
        //'kotlin-android-extensions' plugin in gradle
        button.setOnClickListener { openDialog() }

    }

    private fun openDialog() {
        val exampleDialog = ExampleDialog()
        exampleDialog.show(supportFragmentManager, "example dialog")
    }

    override fun applyTexts(username: String?, password: String?) {
        textViewUsername!!.text = username
        textViewPassword!!.text = password
    }
}

thank you! saved me many searchs!