Fonts in XML android:fontFamily is not applied to toolbars

Question

I'm using the new Fonts in XML feature, which was introduced in Android 8.0 Oreo with the Support Library 26.1.0. The default font family for the whole application is applied by setting the android:fontFamily attribute inside the application theme:

<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
     ...
    <item name="android:fontFamily">@font/proxima_nova</item>
</style>

The font is properly applied to all views in the app except Toolbar. All toolbars keep using the Roboto font:

UPDATE: The issue seems to be fixed in Support Library 27.0.0. I cannot reproduce it any longer.

Answer 1

I've not yet tested on all Android version but this seems to work:

<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
     ...
    <item name="android:fontFamily">@font/proxima_nova</item>
    <item name="toolbarStyle">@style/AppTheme.Toolbar</item>
</style>

<style name="AppTheme.Toolbar" parent="Widget.AppCompat.Toolbar">
    <item name="titleTextAppearance">@style/AppTheme.ToolbarTextStyle</item>
</style>

<style name="AppTheme.ToolbarTextStyle" parent="TextAppearance.Widget.AppCompat.Toolbar.Title">
    <item name="android:fontFamily">@font/proxima_nova</item>
    <item name="fontFamily">@font/proxima_nova</item>
</style>

Answer 2

I spent quite a while to figure this out (even with Support Library 27.1.0). So, here's my solution to this:

<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <!-- Customize your theme here. -->
    <item name="android:fontFamily">@font/proxima_nova</item> <!-- Default app font -->
    <item name="actionBarStyle">@style/Custom.ActionBar</item>
</style>

<style name="Custom.ActionBar" parent="Widget.AppCompat.ActionBar">
    <item name="background">@color/colorPrimary</item>
    <item name="titleTextStyle">@style/Custom.ActionBar.Title</item>
</style>

<style name="Custom.ActionBar.Title" parent="TextAppearance.AppCompat.Widget.ActionBar.Title">
    <item name="android:fontFamily">@font/proxima_nova_bold</item>
</style>

As you can see, instead of referencing Toolbar, I got it to work by referencing ActionBar instead. With the above, the default font for the whole app is Proxima Nova (Regular), while the Toolbar/Action Bar is set to Proxima Nova Bold.

Some context:
For the life of me, I could not get custom font to work using a font xml (where you should set the normal & italic font for regular & bold). So, the @font/proxima_nova_bold in the code links to the font file itself, res/font/proxima_nova_bold.ttf, which works fine.