BottomNavigationView.setupWithNavController 不工作

Question

目前我正在开发一个 Android 应用程序，我想在其中同时使用 Android Navigation Component 和 BottomNavigationView。

在开发上述应用程序时，我查看了官方代码实验室并在此处提出了几个问题，但事实证明它们没有任何帮助。

问题是将 navController 分配给我的 BottomNavigationView 似乎没有任何效果 - 单击菜单项不会影响导航主机。

我的代码：

main_activity.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayoutxmlns: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"
    tools:context=".MainActivity">

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/main_host_fr"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:navGraph="@navigation/nav_graph" />

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/main_nav_bnv"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom"
        android:background="@android:color/transparent"
        android:elevation="0dp"
        app:elevation="0dp"
        app:menu="@menu/menu_main" />

</androidx.coordinatorlayout.widget.CoordinatorLayout>

MainActivity.kt

import android.os.Bundle
import android.os.PersistableBundle
import android.view.MenuItem
import androidx.appcompat.app.AppCompatActivity
import androidx.navigation.findNavController
import androidx.navigation.fragment.NavHostFragment
import androidx.navigation.ui.NavigationUI
import androidx.navigation.ui.setupWithNavController
import com.aredruss.qurio.databinding.ActivityMainBinding
import com.aredruss.qurio.helpers.viewBinding

class MainActivity : AppCompatActivity() {

    // ViewBindingDelegate
    private val binding: ActivityMainBinding by viewBinding(ActivityMainBinding::inflate)

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

    // Using onPostCreate because accessing NavHost in OnCreate causes crashes
    override fun onPostCreate(savedInstanceState: Bundle?, persistentState: PersistableBundle?) {
        super.onPostCreate(savedInstanceState, persistentState)
        binding.navigationBb.setupWithNavController(findNavController(R.id.main_host_fr))
        NavigationUI.setupWithNavController(binding.mainNavBnv, findNavController(R.id.main_host_fr))
    }
}

nav_graph.xml

<?xml version="1.0" encoding="utf-8"?>
<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_graph"
    app:startDestination="@id/action_history">

    <fragment
        android:id="@+id/action_history"
        android:name="com.aredruss.qurio.ui.HistoryFragment"
        android:label="HistoryFragment"
        tools:layout="@layout/fragment_history" >
    </fragment>
  
    <fragment
        android:id="@+id/action_settings"
        android:name="com.aredruss.qurio.ui.SettingsFragment"
        android:label="SettingsFragment"
        tools:layout="@layout/fragment_settings" >
    </fragment>
</navigation>

menu_main.xml

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <item
        android:id="@+id/action_history"
        android:icon="@drawable/ic_history"
        android:title="History"
        app:showAsAction="withText" />

    <item
        android:id="@+id/action_settings"
        android:title="Settings"
        android:icon="@drawable/ic_settings"
        app:showAsAction="withText"
        />
</menu>

我已经检查了 this 解决方案，但没有任何帮助。

Answer 1

以下是需要解决的问题：

您正在使用自动处理 setContentView 的 ViewBindingDelegate，因此您需要删除它，因为在这种情况下您将无法使用 binding.xx：

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    // setContentView(R.layout.activity_main) //<<<<< remove this
    
}

你use onPostCreate while it should not be implemented by developers, and only need to be touched by the system:

Called when activity start-up is complete (after onStart() and onRestoreInstanceState(Bundle) have been called). Applications will generally not implement this method; it is intended for system classes to do final initialization after application code has run.

根据我的测试，onPostCreate() 没有被调用。因此，要解决此问题，请将这部分代码移动到可以由 onStart() 或 onResume():

等开发人员实现的生命周期方法

override fun onStart() {
    super.onStart()
    NavigationUI.setupWithNavController(
        binding.mainNavBnv,
        findNavController(R.id.main_host_fr)
    )
}

这样 NavController 可以自动处理 BottomNavigationView:

UPDATE：根据评论，您应该按如下方式使用 NavHostFragment 获取 NavController，因此您可以将代码传输到 onCreate()方法：

val navHostFragment =
    supportFragmentManager.findFragmentById(R.id.main_host_fr) as NavHostFragment
val navController = navHostFragment.navController

Answer 2

你覆盖错了onPostCreate():

override fun onPostCreate(savedInstanceState: Bundle?, persistentState: PersistableBundle?) {

您不想要带 PersistableBundle 的那个 - 您想要普通的：

override fun onPostCreate(savedInstanceState: Bundle?) {

现在您的 onPostCreate() 将真正被调用。

当然，您根本不应该使用 onPostCreate()。相反，您应该是 following the documentation，它明确说明您应该使用以下代码在 onCreate() 中获取 NavController：

val navHostFragment =
    supportFragmentManager.findFragmentById(R.id.main_host_fr) as NavHostFragment
val navController = navHostFragment.navController

这让您可以将整个代码编写为：

// ViewBindingDelegate
private val binding: ActivityMainBinding by viewBinding(ActivityMainBinding::inflate)

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    // Note how we actually set the content view from the binding
    setContentView(binding.root)

    val navHostFragment =
        supportFragmentManager.findFragmentById(R.id.main_host_fr) as NavHostFragment
    val navController = navHostFragment.navController

    binding.navigationBb.setupWithNavController(navController)
    binding.mainNavBnv.setupWithNavController(navController)
}

Answer 3

错误导入工具栏时会出现该问题所以首先，尝试删除工具栏导入并将该行添加到栏导入

androidx.appcompat.widget.Toolbar Android X 工具栏

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