如何在片段中显示回按按钮

Question

是的，有很多关于它的结果，我试过，但我找不到正确的答案。我有一个导航图团队。我有一个活动和四个片段。我想把返回按钮放在片段之间的过渡段

Answer 1

只需使用findNavController，它很容易导航，但一定要在导航中添加操作。它会自动添加一个后退按钮。For connect to each other:nav_graph:

<?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/my_nav"
    app:startDestination="@id/firstFragment">
    <fragment
        android:id="@+id/firstFragment"
        android:name="com.example.testbackbutton.FirstFragment"
        android:label="fragment_first"
        tools:layout="@layout/fragment_first" >
        <action
            android:id="@+id/action_firstFragment_to_secondFragment"
            app:destination="@id/secondFragment" />
    </fragment>
    <fragment
        android:id="@+id/secondFragment"
        android:name="com.example.testbackbutton.SecondFragment"
        android:label="fragment_second"
        tools:layout="@layout/fragment_second" >
        <action
            android:id="@+id/action_secondFragment_to_firstFragment"
            app:destination="@id/firstFragment" />
    </fragment>
</navigation>

MainActivity:

class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)
        setupActionBarWithNavController(findNavController(R.id.fragmentContainerView))
    }
    override fun onSupportNavigateUp(): Boolean {
        val navController = findNavController(R.id.fragmentContainerView)
        return navController.navigateUp() or super.onSupportNavigateUp()
    }
}

第一个片段:

class FirstFragment : Fragment() {
    private var _binding: FragmentFirstBinding? = null
    private val binding get() = _binding!!
    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment

        _binding = FragmentFirstBinding.inflate(inflater, container, false)
        binding.btn.setOnClickListener{
            findNavController().navigate(R.id.action_firstFragment_to_secondFragment)
        }
        return binding.root
    }
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        setHasOptionsMenu(true)
    }
} 

第一个片段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"
    tools:context=".FirstFragment">
    <!-- TODO: Update blank fragment layout -->
    <Button
        android:id="@+id/btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_blank_fragment"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

第二个片段是默认的。点击第一个片段上的按钮，然后你会看到第二个片段上的后退按钮。