kotlin 通知する

import android.app.NotificationChannel
import android.app.NotificationManager
import android.content.Context
import android.os.Build
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.core.app.NotificationCompat
import androidx.core.app.NotificationManagerCompat
import com.example.samplenotification.databinding.ActivityMainBinding

class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        binding.btnTest.setOnClickListener {
          val channelId = "com.example.sample_notification"
            val channelName = "my channel"
            val channelDescription = "This is a sample notification."

            //Android 8.0 以上ではアプリの通知チャンネルを登録することが必要。
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) { //---*0
                val importance = NotificationManager.IMPORTANCE_DEFAULT //---*1
                val channel = NotificationChannel(channelId, channelName, importance).apply {
                  description = channelDescription
                }
              val manager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
                manager.createNotificationChannel(channel)
            }

            //通知をシステムに登録しています。
            val builder = NotificationCompat.Builder(this, channelId).apply {
              setSmallIcon(R.drawable.ic_launcher_foreground) //---*2
                setContentTitle("通知のタイトル")
                setContentText("通知するメッセージ")
                priority = NotificationCompat.PRIORITY_DEFAULT //---*3
            }
          val id = 0 //---*4
            NotificationManagerCompat.from(this).notify(id, builder.build())
        }
    }
}