使用工具栏处理导航组件中的物理后退按钮

Question

I have a simple proof of concept app that contains only 2 fragments: MainFragment and RepositoryFragment and 1 activity: MainActivity

Here's my 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/nav_graph"
    app:startDestination="@id/id_main">

    <fragment
        android:id="@+id/id_main"
        android:name="com.repofetcher.main.view.MainFragment"
        android:label="@string/app_name"
        tools:layout="@layout/main_fragment">
        <action
            android:id="@+id/action_mainfragment_to_repositoryfragment"
            app:destination="@id/id_repo"
            app:popUpTo="@id/id_main"
            app:popUpToInclusive="true"/>
    </fragment>

    <fragment
        android:id="@+id/id_repo"
        android:name="com.repofetcher.repo.view.RepositoryFragment"
        android:label="{arg_repo_name}"
        tools:layout="@layout/repository_fragment">
        <argument
            android:name="arg_repo_name"
            app:argType="string"
            android:defaultValue="@null"
            app:nullable="true" />
    </fragment>

</navigation>

MainActivity:

    private lateinit var navController: NavController

    override fun onCreate(savedInstanceState: Bundle?) {
        (application as RepoFetcherApplication).appComponent.mainComponent().create().inject(this)
        super.onCreate(savedInstanceState)
        setContentView(R.layout.main_activity)
        navController = findNavController(R.id.nav_host_fragment)
        setupActionBarWithNavController(navController)
    }

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

Main activity's layout:

<?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=".main.view.MainActivity">

    <fragment
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/nav_graph" />

</androidx.constraintlayout.widget.ConstraintLayout>

This is the part that navigates from MainFragment to RepositoryFragment

    private fun navToRepositoryFragment(name: String) {
        findNavController().navigate(MainFragmentDirections.actionMainfragmentToRepositoryfragment(argRepoName = name))
    }

RepositoryFragment:

 override fun onCreate(savedInstanceState: Bundle?) {
        (requireActivity().application as RepoFetcherApplication).appComponent.repoComponent().create().inject(this)
        super.onCreate(savedInstanceState)
    }

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        dataBinding = DataBindingUtil.inflate(inflater, R.layout.repository_fragment, container, false)
        dataBinding.lifecycleOwner = this
        viewModel = ViewModelProvider(this, viewModelProviderFactory).get(RepositoryViewModel::class.java)
        dataBinding.viewModel = viewModel
        return dataBinding.root
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        viewModel.getRepository(args.argRepoName)
    }

Ideally, I would like to achieve these navigations:

navigating from MainFragment to RepositoryFragment , then by clicking either the back button on the Toolbar or on the device, it should navigate back to the MainFragment .

However in my case, only the back button on the toolbar will work as intended. The back button on the device will directly quit the app.

I wonder what I'm missing in the code?

Update

One of the real problem behind this question is I used livedata for a single event (to handle the click event in order to navigate to RepositoryFragment ).

So after taking a look at this article: https://proandroiddev.com/livedata-with-single-events-2395dea972a8

with solution @GabrieleMariotti provided and got the problem solved.

I would like to thank @GabrieleMariotti who helped me with great patient.

Answer 1

Remove the app:popUpTo="@id/id_main" and app:popUpToInclusive="true in your action :

    <action
        android:id="@+id/action_mainfragment_to_repositoryfragment"
        app:destination="@id/nav_gallery"
        />

In your onCreate method use:

    appBarConfiguration = AppBarConfiguration(navController.graph)
    setupActionBarWithNavController(navController, appBarConfiguration)

and in your onSupportNavigateUp method:

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