add second fragment in activity

MainActivity.kt

package com.ascedncorp.androidbasic

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import com.ascedncorp.androidbasic.databinding.ActivityMainBinding

class MainActivity: AppCompatActivity() {

    private val binding: ActivityMainBinding by lazy {
        ActivityMainBinding.inflate(layoutInflater)
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(binding.root)

        if (savedInstanceState == null) {
            supportFragmentManager.beginTransaction()
                .replace(R.id.container, MainFragment.newInstance())
                .commit()
        }
    }

    fun openSecondFragment(text: String) {
        supportFragmentManager.beginTransaction()
            .add(R.id.container, SecondFragment.newInstance(text))
            .addToBackStack(null)
            .commit()
    }
}

MainFragment.kt

package com.ascedncorp.androidbasic

import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import com.ascedncorp.androidbasic.databinding.FragmentMainBinding

class MainFragment: Fragment() {

    private lateinit var binding: FragmentMainBinding

    companion object {
        fun newInstance() = MainFragment()
    }

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?,
    ): View {
        binding = FragmentMainBinding.inflate(inflater, container, false)
        return binding.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        binding.button.setOnClickListener {
            (requireActivity() as MainActivity).openSecondFragment(binding.edittext.text.toString())
        }
    }
}