为了在切换底部标签时不销毁Fragment视图，可以使用以下代码。

首先，我们需要在MainActivity中定义NavController，并使用onSaveInstanceState保留当前Fragment的状态。

class MainActivity : AppCompatActivity() {

    private lateinit var navController: NavController

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

        // Initialize NavController
        navController = Navigation.findNavController(this, R.id.nav_host_fragment)

        if (savedInstanceState == null) {
            navController.navigate(R.id.homeFragment)
        }
    }

    override fun onSaveInstanceState(outState: Bundle) {
        super.onSaveInstanceState(outState)
        Navigation.findNavController(this, R.id.nav_host_fragment).let {
            outState.putInt("currentDestinationId", it.currentDestination?.id ?: R.id.homeFragment)
        }
    }

    override fun onRestoreInstanceState(savedInstanceState: Bundle) {
        super.onRestoreInstanceState(savedInstanceState)
        Navigation.findNavController(this, R.id.nav_host_fragment).apply {
            val currentDestinationId = savedInstanceState.getInt("currentDestinationId", R.id.homeFragment)
            if (currentDestination?.id != currentDestinationId) {
                navigate(currentDestinationId)
            }
        }
    }

    override fun onSupportNavigateUp(): Boolean {
        return navController.navigateUp() || super.onSupportNavigateUp()
    }
}

接下来，在Fragment中使用onCreateView和onDestroyView来保存和恢复Fragment视图的状态。

class MyFragment : Fragment() {

    private var hasViewCreated: Boolean = false

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        val view = inflater.inflate(R.layout.fragment_my, container, false)
        if (!hasViewCreated) {
            // Do initialization here
            hasViewCreated = true
        } else {
            // Restore state here
        }
        return view
    }

    override fun onDestroyView() {
        super.onDestroyView()
        hasViewCreated = false
    }

}

当Fragment视图被创建时，我们进行初始化。当Fragment被销毁并重新创建时，我们将恢复保存的状态。在每个Fragment中使用这些代码来存储和恢复Fragment视图状态，就可以在切换底部标签时不销毁Fragment视图了。