返回到上一个片段- NavGraph

Question

我使用NavGraph导航UI组件从一个片段导航到另一个片段。

设备用于导航的物理按钮，但如何激活应用程序顶部的后退箭头才能返回到上一个片段

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NavGraph

 <?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 -目前这并不能做太多事情

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)
    }
}

活动

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)
    }
}

编辑

将活动代码更新为此，并且它起作用了

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()
    }
}

谢谢R

Answer 1

我们称之为“向上”导航按钮。有关此问题的讨论，请参阅此处：

How to handle up button inside fragment using Navigation Components

解决方案至少需要使用setupActionBarWithNavController()方法。

Answer 2

只需将onSupportNavigateUp()添加到主活动中

override fun onSupportNavigateUp() = navController.navigateUp()

Answer 3

如果您使用导航抽屉布局实现此功能，则使用此行返回到上一个片段，但如果您希望使用底部导航和导航抽屉布局click here来实现导航组件。只是为了将来的帮助做个解释。

appBarConfiguration = AppBarConfiguration(navController.graph, drawerLayoutID)
NavigationUI.setupActionBarWithNavController(this, navController,
     drawerLayoutID)