启动Android应用时NavController未设置致RuntimeException错误求助

启动Android应用时触发如下错误：

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.roomapp/com.example.roomapp.MainActivity}: java.lang.IllegalStateException: Activity com.example.roomapp.MainActivity@1a747ad does not have a NavController set on 2131230894

相关代码如下：

MainActivity.kt #

package com.example.roomapp

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.navigation.findNavController
import androidx.navigation.ui.setupActionBarWithNavController

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

        setupActionBarWithNavController(findNavController(R.id.fragmentContainerView))
    }

    override fun onSupportNavigateUp(): Boolean {
        val navController = findNavController(R.id.fragmentContainerView)
        return navController.navigateUp() || super.onSupportNavigateUp()
    }
}

activity_main.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"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/fragmentContainerView"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:navGraph="@navigation/my_nav" />
</androidx.constraintlayout.widget.ConstraintLayout>

AndroidManifest.xml #

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">

    <application
        android:allowBackup="true"
        android:dataExtractionRules="@xml/data_extraction_rules"
        android:fullBackupContent="@xml/backup_rules"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.RoomApp"
        tools:targetApi="31">
        <activity
            android:name=".MainActivity"
            android:exported="true"
            android:label="@string/app_name"
            android:theme="@style/Theme.AppCompat">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

这个错误的核心原因是：使用FragmentContainerView承载NavHostFragment时，在Activity的onCreate阶段直接调用findNavController()会失败——此时NavHostFragment还未完成依附，系统找不到对应的NavController。

修改MainActivity.kt代码，通过supportFragmentManager获取NavHostFragment实例，再从中获取NavController：

package com.example.roomapp

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.navigation.fragment.NavHostFragment
import androidx.navigation.ui.setupActionBarWithNavController

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

        // 替换原有的findNavController调用
        val navHostFragment = supportFragmentManager.findFragmentById(R.id.fragmentContainerView) as NavHostFragment
        val navController = navHostFragment.navController
        setupActionBarWithNavController(navController)
    }

    override fun onSupportNavigateUp(): Boolean {
        val navHostFragment = supportFragmentManager.findFragmentById(R.id.fragmentContainerView) as NavHostFragment
        val navController = navHostFragment.navController
        return navController.navigateUp() || super.onSupportNavigateUp()
    }
}

另外需要确认：

• @navigation/my_nav导航图文件存在，且已正确配置起始目的地（app:startDestination）
• 依赖库中已引入Navigation相关组件（如androidx.navigation:navigation-fragment-ktx、androidx.navigation:navigation-ui-ktx）

内容的提问来源于stack exchange，提问作者miq