Android Navigation Component back button not working

if you are using setupActionBarWithNavController in Navigation Component such as:

 setupActionBarWithNavController(findNavController(R.id.fragment))

then also override and config this methods in your main activity:

 override fun onSupportNavigateUp(): Boolean {
    val navController = findNavController(R.id.fragment)
    return navController.navigateUp() || super.onSupportNavigateUp()
}

My MainActivity.kt

class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    setupActionBarWithNavController(findNavController(R.id.fragment))
}

override fun onSupportNavigateUp(): Boolean {
    val navController = findNavController(R.id.fragment)
    return navController.navigateUp() || super.onSupportNavigateUp()
}
}