Android Kotlin在某些片段中显示导航抽屉图标而不是“后退按钮"

我想在某个片段上显示导航抽屉图标而不是后退"按钮.我创建了带有导航图的应用程序.

I want to show navigation drawer icon instead of Back button on a certain fragment. I created the App with Navigation graph.

假设我有2个片段(LoginFragment和DashboardFragment)和一个活动(MainActivity)

Let's say i have 2 fragments (LoginFragment and DashboardFragment) and one activity (MainActivity)

MainActivity.kt

class MainActivity : AppCompatActivity() {

    lateinit var drawerLayout: DrawerLayout

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

        val binding = DataBindingUtil.setContentView<ActivityMainBinding>(this, R.layout.activity_main)
        drawerLayout = binding.drawerLayout

        val navController = this.findNavController(R.id.myNavHostFragment)

        // prevent nav gesture if not on start destination
        navController.addOnDestinationChangedListener { nc: NavController, nd: NavDestination, args: Bundle? ->
            if (nd.id == nc.graph.startDestination) {
                drawerLayout.setDrawerLockMode(DrawerLayout.LOCK_MODE_UNLOCKED)
            } else {
                drawerLayout.setDrawerLockMode(DrawerLayout.LOCK_MODE_LOCKED_CLOSED)
            }
        }

        NavigationUI.setupActionBarWithNavController(this, navController, drawerLayout)
        NavigationUI.setupWithNavController(binding.navView, navController)

    }


    // Set up the back button on action bar
    override fun onSupportNavigateUp(): Boolean {
        val navController = this.findNavController(R.id.myNavHostFragment)

        return NavigationUI.navigateUp(navController, drawerLayout)
    }
}

LoginFragment.kt

class LoginFragment : Fragment() {

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val binding:FragmentLoginBinding = DataBindingUtil.inflate(inflater,
            R.layout.fragment_login, container, false)

        // Hide the Action bar
        (activity as AppCompatActivity).supportActionBar?.hide()

        binding.loginButton.setOnClickListener {
           //Some unimportant validation
        }


        return binding.root
    }

}

DashboardFragment.kt

class DashboardFragment : Fragment() {

    lateinit var binding : FragmentDashboardBinding

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {

        // Binding object for this fragment and the layout
        binding = DataBindingUtil.inflate(inflater,
            R.layout.fragment_dashboard, container, false)

        //Navigate to Product stock fragment when clicked
        binding.productStockButton.setOnClickListener(Navigation.createNavigateOnClickListener(
            R.id.action_dashboardFragment_to_productStockOutletList
        ))

        //Navigate to Switching History fragment when clicked
        binding.switchingHistoryButton.setOnClickListener(Navigation.createNavigateOnClickListener(
            R.id.action_dashboardFragment_to_switchingHistoryFragment
       ))

        //Navigate to Outlet List fragment for Outstanding Product when clicked
        binding.outstandingOrderButton.setOnClickListener(Navigation.createNavigateOnClickListener(
            R.id.action_dashboardFragment_to_outletListFragment
        ))


        // Set action bar title to "Main Dashboard"
        (activity as AppCompatActivity).supportActionBar?.title = "Main Dashboard"

        // Declare that this fragment has menu
        setHasOptionsMenu(true)

        (activity as AppCompatActivity).supportActionBar?.show()
        (activity as AppCompatActivity).supportActionBar?.setDisplayHomeAsUpEnabled(false)


        //Return.... i don't know.
        return binding.root
    }

    override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
        super.onCreateOptionsMenu(menu, inflater)
        inflater?.inflate(R.menu.nav_overflow_menu, menu)
    }
}

这是我的导航图(我将LoginFragment设置为主页)

我想在DashboardFragment中显示导航抽屉，而不是LoginFragment. (使用LoginFragment仍然是图形的开始).我已经隐藏了DashboardFragment的向上"按钮

I want to show the navigation drawer in the DashboardFragment instead of LoginFragment. (With LoginFragment still be the start of the graph). I already hide the Up button of the DashboardFragment

这是仪表板的当前外观.如您所见，后退按钮已经消失.

This is the current look of the dashboard. As you can see that the back button is already gone.

我有什么可以做的吗?如果有不清楚的地方，请通知我.

Is there anything i can do with it ? If there is something unclear let me know.