Error calling setSupportActionBar in a Fragment in Kotlin

Question

I am trying to set up a toolbar in a fragment.

Whilst the Google Developer docs have been updated to include Kotlin code (see this page):

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_my)
    // Note that the Toolbar defined in the layout has the id "my_toolbar"
    setSupportActionBar(findViewById(R.id.my_toolbar))

it relates to the setup of a toolbar in an activity as opposed to a fragment.

I found this SO post which suggests that you can't just call setSupportActionBar in a fragment. To quote:

Fragments don't have such method setSupportActionBar(). ActionBar is a property of Activity, so to set your toolbar as the actionBar, your activity should extend from ActionBarActivity and then you can call in your Fragment:

...

If you're using AppCompatActivity:

((AppCompatActivity)getActivity()).setSupportActionBar(mToolbar);

However the code given above is in java.

How do I call this in Kotlin?

Answer 1

To access the ActionBar from a Fragment in Kotlin:

if(activity is AppCompatActivity){
        (activity as AppCompatActivity).setSupportActionBar(mToolbar)
    }

To set an ActionBar title from a Fragment you can do

(activity as AppCompatActivity).supportActionBar?.title = "Title"

or

(activity as AppCompatActivity).supportActionBar?.setTitle(R.string.my_title_string)

Answer 2

There is an implementation in the Navigation codelab from Google that I think will do what I need: enable customisation of the title, menu items and hook into the up navigation for different fragment contexts. Specifically:

1. The toolbar is included in the main layout xml file (navigation_activity.xml in that codelab) outside of the fragment:

navigation_activity.xml

<LinearLayout>
    <android.support.v7.widget.Toolbar/>
    <fragment/>
    <android.support.design.widget.BottomNavigationView/>
</LinearLayout>

2. Then setup the toolbar in the main activity file as follows:

MainActivity.kt

class MainActivity : AppCompatActivity() {
    private var drawerLayout: DrawerLayout? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.navigation_activity)

        val toolbar = findViewById<Toolbar>(R.id.toolbar)
        setSupportActionBar(toolbar)

        //...

        // Set up Action Bar
        val navController = host.navController
        setupActionBar(navController)

        //...

    }

    private fun setupActionBar(navController: NavController) {
        drawerLayout = findViewById(R.id.drawer_layout)

        NavigationUI.setupActionBarWithNavController(this, navController, drawerLayout)
    }

    override fun onCreateOptionsMenu(menu: Menu): Boolean {
        val retValue = super.onCreateOptionsMenu(menu)
        val navigationView = findViewById<NavigationView>(R.id.nav_view)
        // The NavigationView already has these same navigation items, so we only add
        // navigation items to the menu here if there isn't a NavigationView
        if (navigationView == null) {
            menuInflater.inflate(R.menu.menu_overflow, menu)
            return true
        }
        return retValue
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        // Have the NavHelper look for an action or destination matching the menu
        // item id and navigate there if found.
        // Otherwise, bubble up to the parent.
        return NavigationUI.onNavDestinationSelected(item,
                Navigation.findNavController(this, R.id.my_nav_host_fragment))
                || super.onOptionsItemSelected(item)
    }

    override fun onSupportNavigateUp(): Boolean {
        return NavigationUI.navigateUp(drawerLayout,
                Navigation.findNavController(this, R.id.my_nav_host_fragment))
    }
}

3. Then in the fragment file you can inflate further menu items. In the codelab, main_menu.xml contains a shopping cart item which is added to the overflow setup in the main activity above.

MainFragment.kt

class MainFragment : Fragment() {

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                                  savedInstanceState: Bundle?): View? {
            setHasOptionsMenu(true)
            return inflater.inflate(R.layout.main_fragment, container, false)
    }

    override fun onCreateOptionsMenu(menu: Menu?, inflater: MenuInflater?) {
            inflater?.inflate(R.menu.main_menu, menu)
    }
}