How do pass values to a parameterized label?

The navigation components use the value in `android:label` to set the [toolbar] title depending on where in the navigation graph the use has navigated to. This works fine except I want to have the title reflect the category of things the screen is referring to, but the specific thing that the user is about to edit.

Normally I would have piece of code like `updateTitle` below on the activity and then call it from the fragment (onResume) with:

``` kotlin
updateTitle(getString(R.string.book_title, bookNumber))
```

but this does not work unless I also remove the `android:label` attribute from the nav_graph.xml.

Component used:
'android.arch.navigation:navigation-fragment-ktx:1.0.0-alpha01'
'android.arch.navigation:navigation-ui-ktx:1.0.0-alpha01'
Version used:
as above

Devices/Android versions reproduced on:
All

- Sample project to trigger the issue.
``` xml
// snippet from nav_graph.xml
<fragment
android:id="@+id/bookFragment"
android:name="com.example.bookFragment"
android:label="@string/book_title" >
<argument
android:name="bookId"
app:type="integer" />
</fragment>

// snippet from sttrings.xml
<string name="book_title">book %1$d</string>
```
Some snippets from the way I would otherwise do it.

``` kotlin
// actrivity, implements updateTitle( from an interface (Foo)
override fun updateTitle(title: String) {
toolbar?.title = title
}
// fragment
override fun onResume() {
super.onResume()
// foo is the activity cast to Foo
foo?.updateTitle(getString(R.string.reading_title, 1))
}
```

- A screenrecord or screenshots showing the issue (if UI related).

Actual title vs expected