android - 使用带有导航架构组件的底部菜单栏时如何从工具栏中删除后退按钮

Question

我有一个应用程序，它有一个底部菜单栏，用户可以使用它在 4 个主页选项卡之间切换。它工作正常，如下所示。

我遇到的唯一问题是当我在不同 fragment 之间切换时它显示返回按钮。由于所有这些 fragment 都处于同一级别，我不希望它表现得那样。
这是我的实现。
主导航 Activity

class MainNavigationActivity : AppCompatActivity() {

    private lateinit var navigationController: NavController

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

        initialization()
    }

    private fun initialization(){

        navigationController = Navigation.findNavController(this, R.id.hostFragment)

        setSupportActionBar(toolbar)
        NavigationUI.setupWithNavController(bottomNavigationBar,navigationController)
        NavigationUI.setupActionBarWithNavController(this,navigationController)
    }

override fun onBackPressed() {
        onSupportNavigateUp()
    }

MainNavigationActivity 布局

<RelativeLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".activities.MainNavigationActivity">

    <androidx.appcompat.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentTop="true"
            android:background="@color/colorPrimary"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
            app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"/>

    <fragment
            android:id="@+id/hostFragment"
            android:name="androidx.navigation.fragment.NavHostFragment"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_below="@id/toolbar"
            android:layout_above="@id/bottomNavigationBar"
            app:defaultNavHost="true"
            app:navGraph="@navigation/main_navigation_graph" />

    <com.google.android.material.bottomnavigation.BottomNavigationView
            android:id="@+id/bottomNavigationBar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:background="@android:color/white"
            app:menu="@menu/bottom_navigation_menu"
            app:labelVisibilityMode="labeled"/>

</RelativeLayout>

bottom_navigation_menu.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
            android:id="@+id/navigation_home"
            android:state_checked="true"
            android:color="@color/colorPrimary"
            android:title="@string/navigation_home"
            android:icon="@drawable/ic_bottom_bar_menu_home"/>
    <item
            android:id="@+id/navigation_offers"
            android:state_checked="false"
            android:color="@color/gray"
            android:title="@string/navigation_offers"
            android:icon="@drawable/ic_bottom_bar_menu_offers"/>

    <item
            android:id="@+id/navigation_my_bookings"
            android:state_checked="false"
            android:color="@color/gray"
            android:title="@string/navigation_my_bookings"
            android:icon="@drawable/ic_bottom_bar_menu_bookings"/>
    <item
            android:id="@+id/navigation_my_account"
            android:state_checked="false"
            android:color="@color/gray"
            android:title="@string/navigation_my_account"
            android:icon="@drawable/ic_bottom_bar_menu_account"/>
</menu>

导航图中的 fragment 的 ID 和 menu.xml 中的 ID 相同。这就是它识别正确 fragment 并正确切换到该 fragment 的方式。
如何在主屏幕级别的工具栏上删除此后退按钮？

Answer 1

根据 the NavigationUI documentation :

By default, the Navigation button is hidden when a user is at a top-level destination of a navigation graph and appears as an Up button in any other destination.

If you want to customize which destinations are considered top-level destinations, you can instead pass a set of destination IDs to the constructor, as shown below:

val appBarConfiguration = AppBarConfiguration(setOf(
    R.id.navigation_home, R.id.navigation_offers,
    R.id.navigation_my_bookings, R.id.navigation_my_account))

(请注意，此构造函数需要 navigation-ui-ktx 工件 - 替代方法是使用 AppBarConfiguration.Builder )