如何解决如何在 Fragment 中设置 BottomNavigationView
我有一个活动和几个片段。我使用 NavController
和导航图设置了我的活动,如下所示:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
val navHostFragment = supportFragmentManager
.findFragmentById(R.id.nav_host_activity_main) as NavHostFragment
navController = navHostFragment.findNavController()
}
override fun onSupportNavigateUp(): Boolean {
return navController.navigateUp() || super.onSupportNavigateUp()
}
在这个导航图中,我负责启动画面、登录、注册片段和转到主片段,其中包含一个 BottomNavigationView
和两个子片段。
我为 bottomNavView 片段制作了一个菜单并为它们制作了一个图表,菜单 ID 与底部导航图表 ID 匹配。
我的布局如下:
<androidx.fragment.app.FragmentContainerView
android:id="@+id/nav_host_fragment_main"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="0dp"
android:layout_height="0dp"
app:defaultNavHost="true"
app:layout_constraintBottom_toTopOf="@+id/bottom_Navigation_view"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:navGraph="@navigation/bottom_view_nav_graph" />
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="@+id/bottom_Navigation_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@color/white"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:menu="@menu/bottom_nav_menu" />
</androidx.constraintlayout.widget.ConstraintLayout>
在主要片段中,我尝试使用如下导航图设置底部导航视图:
override fun onViewCreated(view: View,savedInstanceState: Bundle?) {
super.onViewCreated(view,savedInstanceState)
val appCompat = requireActivity() as AppCompatActivity
val navHostFragment = appCompat.supportFragmentManager.findFragmentById(R.id.nav_host_fragment_main) as NavHostFragment
val navController = navHostFragment.findNavController()
binding.bottomNavigationView.setupWithNavController(navController)
}
但是我不断收到此异常:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.ak.chatter,PID: 1937
java.lang.NullPointerException: null cannot be cast to non-null type androidx.navigation.fragment.NavHostFragment
at com.ak.chatter.ui.main.MainFragment.onViewCreated(MainFragment.kt:34)
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:332)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1187)
at androidx.fragment.app.FragmentManager.addAddedFragments(FragmentManager.java:2224)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1997)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1953)
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1849)
at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413)
at android.os.Handler.handleCallback(Handler.java:900)
at android.os.Handler.dispatchMessage(Handler.java:103)
at android.os.Looper.loop(Looper.java:219)
at android.app.ActivityThread.main(ActivityThread.java:8347)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1055)
解决方法
java.lang.NullPointerException: null cannot be cast to non-null type
androidx.navigation.fragment.NavHostFragment
您尝试将空值转换为非空值。
null
来自 appCompat.supportFragmentManager.findFragmentById(R.id.nav_host_fragment_main)
因为您使用 supportFragmentManager
作为由片段托管的片段的片段管理器。
您应该将 childFragmentManager
用于由另一个片段托管的片段。
所以,为了解决这个问题,将主片段类中的 supportFragmentManager
替换为 childFragmentManager
override fun onViewCreated(view: View,savedInstanceState: Bundle?) {
super.onViewCreated(view,savedInstanceState)
val appCompat = requireActivity() as AppCompatActivity
val navHostFragment = appCompat.childFragmentManager.findFragmentById(R.id.nav_host_fragment_main) as NavHostFragment
val navController = navHostFragment.findNavController()
binding.bottomNavigationView.setupWithNavController(navController)
}
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