android navigation pass arguments to fragment constructor

Issue

I have created Navigation Drawer Activity:

class MainActivity : AppCompatActivity() {

    private lateinit var appBarConfiguration: AppBarConfiguration

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val toolbar: Toolbar = findViewById(R.id.toolbar)
        setSupportActionBar(toolbar)

        val drawerLayout: DrawerLayout = findViewById(R.id.drawer_layout)
        val navView: NavigationView = findViewById(R.id.nav_view)
        val navController = findNavController(R.id.nav_host_fragment)

        appBarConfiguration = AppBarConfiguration(navController.graph, drawerLayout)
        setupActionBarWithNavController(navController, appBarConfiguration)
        navView.setupWithNavController(navController)
    }
}

And I have mobile_navigation.xml:

<?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/mobile_navigation"
    app:startDestination="@id/databaseFragment">
    <fragment
        android:id="@+id/databaseFragment"
        android:name="com.acmpo6ou.myaccounts.ui.DatabaseFragment"
        android:label="fragment_database_list"
        tools:layout="@layout/fragment_database_list" >
        <action
            android:id="@+id/actionCreateDatabase"
            app:destination="@id/createDatabaseFragment" />
    </fragment>
    <fragment
        android:id="@+id/createDatabaseFragment"
        android:name="com.acmpo6ou.myaccounts.ui.CreateDatabaseFragment"
        android:label="create_edit_database_fragment"
        tools:layout="@layout/create_edit_database_fragment" />
</navigation>

The start destination is DatabaseFragment. However there is a problem, here is my DatabaseFragment:

class DatabaseFragment(
        override val adapter: DatabasesAdapterInter,
        val presenter: DatabasesPresenterInter
) : Fragment(), DatabaseFragmentInter {
...
    companion object {
        @JvmStatic
        fun newInstance(
                adapter: DatabasesAdapterInter,
                presenter: DatabasesPresenterInter
        ) = DatabaseFragment(adapter, presenter)
    }
}

As you can see my DatabaseFragment should receive two arguments to its constructor: adapter and presenter. This is because of dependency injection, in my tests I can instantiate DatabaseFragment passing through mocked adapter and presenter. Like this:

...
val adapter = mock<DatabasesAdapterInter>()
val presenter = mock<DatabasesPresenterInter>()
val fragment = DatabaseFragment(adapter, presenter)
...

It works with tests, but it doesn't work with android navigation. It seems that Android Navigation Components create DatabaseFragment instead of me, but they don't pass any arguments to fragment's constructor and it fails with error that is too long to post it here.

Is there a way to tell Navigation Components so that they pass appropriate arguments to my fragments when instantiating them?

Thanks!

Solution

Short answer is no, you can not pass arguments to Fragment.

All subclasses of Fragment must include a public no-argument constructor. The framework will often re-instantiate a fragment class when needed, in particular during state restore, and needs to be able to find this constructor to instantiate it. If the no-argument constructor is not available, a runtime exception will occur in some cases during state restore.

Answered By - i30mb1