Fragment 中的 findNavController() 给出“没有设置 NavController”错误

Question

我是 Android 开发的新手，几天来我一直被这个错误困住了……

我有一个 FragmentContainerView 和 BottomNavigationView 活动。 BottomNavigationView 有 2 个片段可供切换：ScanFragment 和 ProfileFragment。

当我切换到 ProfileFragment 并使用以下代码按下按钮 (payMethodButton) 时：

 val payMethodButton = view.findViewById<TableRow>(R.id.trMyPayMethod)
        payMethodButton.setOnClickListener {

    findNavController().navigate(
       R.id.action_profileFragment_to_bankFragment
    )
}

应用程序将崩溃并显示以下错误消息： View androidx.constraintlayout.widget.ConstraintLayout{2aaced1 VE..... ........ 0,0-1080,1668} does not have a NavController set

我究竟做错了什么？ 为什么没有 NavController？

DashboardActivity.kt

package com.app.app.activities.dashboard

import android.os.Bundle
import android.view.View
import androidx.fragment.app.Fragment
import com.google.android.material.bottomnavigation.BottomNavigationView
import com.app.app.R
import com.app.app.activities.BaseActivity
import com.app.app.fragments.ProfileFragment
import com.app.app.fragments.ScanFragment

class DashboardActivity : BaseActivity() {

    private val scanFragment: Fragment = ScanFragment()
    private val profileFragment: Fragment = ProfileFragment()

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

        val navigation = findViewById<View>(R.id.bottomNavigationView) as BottomNavigationView
        navigation.setOnItemSelectedListener { item ->
            when (item.itemId) {
                R.id.navigation_scan -> replaceFragment(scanFragment)
                R.id.navigation_profile -> replaceFragment(profileFragment)
            }
            true
        }

    }

    private fun replaceFragment(fragment: Fragment) {
        val transaction = supportFragmentManager.beginTransaction()
        transaction.replace(R.id.dashboardNavHostFragment, fragment)
        transaction.commit()
    }

}

activity_dashboard.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/dashboardNavHostFragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toTopOf="@+id/bottomNavigationView"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/dashboard_nav" />

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottomNavigationView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/bottom_menu_bar"
        app:itemIconTint="@drawable/bottom_nav_selector"
        app:itemTextAppearanceActive="@style/BottomNavigationView.Active"
        app:itemTextAppearanceInactive="@style/BottomNavigationView"
        app:itemTextColor="@drawable/bottom_nav_selector"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:menu="@menu/bottom_dash_menu" />

</androidx.constraintlayout.widget.ConstraintLayout>

ProfileFragment.kt

package com.app.app.fragments

import android.app.AlertDialog
import android.content.Intent
import android.os.Bundle
import android.view.*
import android.widget.TableRow
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import androidx.navigation.NavHost
import androidx.navigation.Navigation
import androidx.navigation.fragment.NavHostFragment
import androidx.navigation.fragment.findNavController
import com.app.app.BuildConfig
import com.app.app.R
import com.app.app.activities.account.login.LoginActivity


class ProfileFragment : Fragment() {

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        return inflater.inflate(R.layout.fragment_profile, container, false)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        (activity as AppCompatActivity).supportActionBar?.title = "Profile"

        val payMethodButton = view.findViewById<Button>(R.id.btPayMethod)
        payMethodButton.setOnClickListener {

            findNavController().navigate(
                R.id.action_profileFragment_to_bankFragment
            )
        }


    }

}

dashboard_nav.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/dashboard_nav"
    app:startDestination="@id/scanFragment">
    <fragment
        android:id="@+id/scanFragment"
        android:name="com.app.app.fragments.ScanFragment"
        android:label="fragment_scan"
        tools:layout="@layout/fragment_scan" />
    <fragment
        android:id="@+id/profileFragment"
        android:name="com.app.app.fragments.ProfileFragment"
        android:label="fragment_profile"
        tools:layout="@layout/fragment_profile">
        <action
            android:id="@+id/action_profileFragment_to_bankFragment"
            app:destination="@id/bankFragment" />
    </fragment>
    <fragment
        android:id="@+id/bankFragment"
        android:name="com.app.app.fragments.BankFragment"
        android:label="BankFragment"
        tools:layout="@layout/fragment_bank" />
</navigation>

碰撞：

2022-02-04 18:09:44.524 23247-23247/com.app.app E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.app.app, PID: 23247
    java.lang.IllegalStateException: View androidx.constraintlayout.widget.ConstraintLayout{2aaced1 V.E...... ........ 0,0-1080,1668} does not have a NavController set
        at androidx.navigation.Navigation.findNavController(Navigation.java:84)
        at androidx.navigation.fragment.NavHostFragment.findNavController(NavHostFragment.java:120)
        at androidx.navigation.fragment.FragmentKt.findNavController(Fragment.kt:29)
        at com.app.app.fragments.ProfileFragment.onViewCreated$lambda-0(ProfileFragment.kt:45)
        at com.app.app.fragments.ProfileFragment.$r8$lambda$0UCyAyd5HwAmhAbNeILyUNaedgA(Unknown Source:0)
        at com.app.app.fragments.ProfileFragment$$ExternalSyntheticLambda2.onClick(Unknown Source:2)
        at android.view.View.performClick(View.java:7862)
        at android.view.View.performClickInternal(View.java:7831)
        at android.view.View.access$3600(View.java:879)
        at android.view.View$PerformClick.run(View.java:29359)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:237)
        at android.app.ActivityThread.main(ActivityThread.java:8167)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:496)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1100)

Answer 1

我从 Github 下载了一个例子，它帮助我解决了这个问题。

根据示例，这段代码对我有用：

class DashboardActivity : BaseActivity() {

    private lateinit var navController: NavController
    private lateinit var appBarConfiguration: AppBarConfiguration

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

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

        // Setup the bottom navigation view with navController
        val bottomNavigationView = findViewById<BottomNavigationView>(R.id.bottomNavigationView)
        bottomNavigationView.setupWithNavController(navController)

        // Setup the ActionBar with navController and 2 top level destinations
        appBarConfiguration = AppBarConfiguration(
            setOf(R.id.scanFragment, R.id.profileFragment)
        )
        setupActionBarWithNavController(navController, appBarConfiguration)
    }

    override fun onSupportNavigateUp(): Boolean {
        return navController.navigateUp(appBarConfiguration)
    }

}