how to show back press button in a fragment

Question

yes there are a lot of results about it i tried but i couldn't find the right answer. I have a navigation graph team. I have an activity and Four Fragments. I want to put the back press button in the transition between the fragments

Answer 1

Just use findNavController, it is easy to navigate but be sure to add action to your navigation. It will add a back button automatically. 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()
    }
}

First fragment:

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)
    }
} 

First fragment 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>

The second fragment is the default. Click the button on the first fragment then you will see the back button on the second fragment.