BottomNavigationView重装片段

Question

我已经用BottomNavigationView实现了NavController，但是每次单击片段都会重新加载，即使使用了新的导航库更新。我也尝试过setOnNavigationItemReselectedListener，但是它不会触发任何东西。我做错什么了？我知道这个问题已经问过不止一次了，但我觉得我试过所有的问题，但没有一个有效。我希望我能避免用旧库恢复我的代码，或者使用样板解决方案。这是我的代码：

build.gradle (:app)

implementation 'androidx.navigation:navigation-runtime-ktx:2.5.2'
implementation 'androidx.navigation:navigation-fragment-ktx:2.5.2'
implementation 'androidx.navigation:navigation-ui-ktx:2.5.2'

HomeActivity.kt

class HomeActivity : BaseActivity(), NavigationView.OnNavigationItemSelectedListener,
Serializable {
private lateinit var binding: ActivityHomeBinding
private lateinit var navController: NavController
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    binding= ActivityHomeBinding.inflate(layoutInflater)
    setContentView(binding.root)
    val navHostFragment = supportFragmentManager.findFragmentById(R.id.home_container) as NavHostFragment
    navController = navHostFragment.navController
    binding.bottomNavigation.setupWithNavController(navController) 
    }
    }

activity_home.xml

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:openDrawer="start"
    tools:context=".HomeActivity">

        <androidx.fragment.app.FragmentContainerView
            android:id="@+id/home_container"
            android:name="androidx.navigation.fragment.NavHostFragment"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            app:defaultNavHost="true"
            app:layout_constraintBottom_toTopOf="@+id/bottom_navigation"
            app:layout_constraintTop_toBottomOf="@+id/appbar_layout"
            app:navGraph="@navigation/nav_main" />

        <com.google.android.material.bottomnavigation.BottomNavigationView
            android:id="@+id/bottom_navigation"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:menu="@menu/bottom_navigation_menu"
            app:layout_constraintTop_toBottomOf="@+id/home_container"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintHorizontal_bias="0.5"/>

</RelativeLayout>

nav_main.xml

<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/nav_main"
    app:startDestination="@id/firstFragment">

    <fragment
        android:id="@+id/firstFragment"
        android:name="com.projectName.ui.main.ContactsFragment"
        tools:layout="@layout/fragment_contacts" />
    <fragment
        android:id="@+id/secondFragment"
        android:name="com.projectName.SearchFragment"
        android:label="@string/search"
        tools:layout="@layout/search_fragment" />
    <fragment
        android:id="@+id/thirdFragment"
        android:name="com.projectName.ui.main.NotificationsFragment"
        tools:layout="@layout/notifications_fragment" />
    <fragment
        android:id="@+id/fourthFragment"
        android:name="com.projectName.chat.ChatFragment"
        tools:layout="@layout/fragment_main_page" />
</navigation>

bottom_navigation_menu.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <item
        android:id="@+id/firstFragment"
        android:enabled="true"
        android:icon="@drawable/ic_baseline_contacts_24"
        android:title=""
        app:labelVisibilityMode="unlabeled"/>
    <item
        android:id="@+id/secondFragment"
        android:enabled="true"
        android:icon="@drawable/ic_search_white_24dp"
        android:title=""
        app:labelVisibilityMode="unlabeled"/>
    <item
        android:id="@+id/thirdFragment"
        android:enabled="true"
        android:icon="@drawable/ic_baseline_notifications_none_24"
        android:title=""
        app:labelVisibilityMode="unlabeled"/>
    <item
        android:id="@+id/fourthFragment"
        android:enabled="true"
        android:icon="@drawable/ic_message_white_24dp"
        android:title=""
        app:labelVisibilityMode="unlabeled"/>
</menu>

片段

class NotificationsFragment : Fragment() {
    companion object {
        fun newInstance() = NotificationsFragment()
    }
    private lateinit var viewModel: NotificationsViewModel
    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {

        viewModel = ViewModelProvider(this).get(NotificationsViewModel::class.java)
        return inflater.inflate(R.layout.notifications_fragment, container, false)
    }
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
}

我也给了每个布局一个ID，就像savedInstateState文档所建议的那样。

谢谢。

编辑

我无法找到解决问题的方法，所以我在ViewPager2中使用了ViewPager2：

HomePagerAdapter.kt

private val TAB_TITLES = arrayOf(
    Constants.CONTACTS,
    Constants.SEARCH,
    Constants.NOTIFICATIONS,
    Constants.CHATS
)

class HomePagerAdapter(fa: FragmentActivity) : FragmentStateAdapter(fa) {
    override fun getItemCount(): Int = TAB_TITLES.size

    override fun createFragment(position: Int): Fragment {
        return if (getPageTitle(position) == Constants.CONTACTS) {
            ContactsFragment.newInstance()
        } else if (getPageTitle(position) == Constants.SEARCH) {
            SearchFragment.newInstance()
        } else if (getPageTitle(position) == Constants.NOTIFICATIONS) {
            NotificationsFragment.newInstance()
        } else {
            ChatsFragment.newInstance()
        }
    }

    private fun getPageTitle(position: Int): String {
        return TAB_TITLES[position]
    }
}

HomeActivity.kt

class HomeActivity : BaseActivity(), NavigationView.OnNavigationItemSelectedListener,
    Serializable, SearchFragment.OnPersonSelectedListener {

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

    val homePagerAdapter = HomePagerAdapter(this)
    val viewPager: ViewPager2 = findViewById(R.id.home_view_pager)
    viewPager.adapter = homePagerAdapter
    viewPager.isUserInputEnabled = false
    viewPager.offscreenPageLimit = 1
    viewPager.overScrollMode = ViewPager2.OVER_SCROLL_NEVER

    findViewById<BottomNavigationView>(R.id.bottom_navigation)
        .setOnItemSelectedListener {
            when (it.itemId) {
                R.id.firstFragment -> {
                    viewPager.setCurrentItem(0, false)
                    return@setOnItemSelectedListener true
                }
                R.id.secondFragment -> {
                    viewPager.setCurrentItem(1, false)
                    return@setOnItemSelectedListener true
                }
                R.id.thirdFragment -> {
                    viewPager.setCurrentItem(2, false)
                    return@setOnItemSelectedListener true
                }
                R.id.fourthFragment -> {
                    viewPager.setCurrentItem(3, false)
                    return@setOnItemSelectedListener true
                }
                else -> return@setOnItemSelectedListener false
            }

            }
}
}

activity_home.xml

<androidx.viewpager2.widget.ViewPager2
    android:id="@+id/home_view_pager"
    android:layout_width="match_parent"
    android:layout_height="0dp"
 app:layout_constraintBottom_toTopOf="@+id/bottom_navigation"
    app:layout_constraintTop_toBottomOf="@+id/appbar_layout"
 app:layout_behavior="@string/appbar_scrolling_view_behavior" />

<com.google.android.material.bottomnavigation.BottomNavigationView
    android:id="@+id/bottom_navigation"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:menu="@menu/bottom_navigation_menu"
   app:layout_constraintTop_toBottomOf="@+id/home_view_pager"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintHorizontal_bias="0.5"/>

Answer 1

如果我正确地理解了您的问题，那么每当您从一个片段更改到另一个片段时，您都希望通过使用底部导航栏将片段保持其状态。我认为这可能对https://developer.android.com/guide/navigation/multi-back-stacks有帮助。底部导航中的每个选项卡都有自己的图表，当从一个选项卡切换到另一个选项卡时，状态将被保存。如果这能帮到你就告诉我！