Error calling setSupportActionBar in a Fragment in Kotlin - android-fragments

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:
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>
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))
}
}
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)
}
}