使用NavGraph导航时如何启用顶部返回箭头返回上一级Fragment

我使用NavGraph（Navigation UI组件）在不同Fragment之间进行跳转，设备物理返回键可正常完成导航，但不知道如何激活应用顶部的返回箭头，实现返回上一级Fragment的功能。

现有配置 #

NavGraph配置 #

<?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/charactersFragment">

    <fragment
        android:id="@+id/charactersFragment"
        android:name="com.example.breakingbad.CharactersFragment"
        android:label="fragment_characters"
        tools:layout="@layout/fragment_characters" >
        <action
            android:id="@+id/action_charactersFragment_to_characterDetailFragment"
            app:destination="@id/characterDetailFragment" />
    </fragment>
    <fragment
        android:id="@+id/characterDetailFragment"
        android:name="com.example.breakingbad.CharacterDetailFragment"
        android:label="fragment_character_detail"
        tools:layout="@layout/fragment_character_detail" />
</navigation>

CharacterDetailFragment 代码 #

class CharacterDetailFragment : Fragment() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
        }
    }

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

初始MainActivity代码 #

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

        val navController = Navigation.findNavController(this, R.id.fragment)
        NavigationUI.setupActionBarWithNavController(this, navController)
    }
}

只需要在MainActivity中重写onSupportNavigateUp()方法，关联NavController的返回逻辑即可，修改后的完整MainActivity代码如下：

class MainActivity : AppCompatActivity() {

    private lateinit var navController: NavController

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

        navController = Navigation.findNavController(this, R.id.fragment)
        NavigationUI.setupActionBarWithNavController(this, navController)
    }

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

逻辑说明 #

NavigationUI.setupActionBarWithNavController方法只会自动在非起始目的地页面显示顶部返回箭头，但箭头的点击事件默认没有绑定导航逻辑，重写onSupportNavigateUp方法后，点击顶部返回箭头时会触发navController.navigateUp()执行回退操作，和物理返回键的导航逻辑完全一致。

内容的提问来源于stack exchange，提问作者BRDroid