font_style.xml

<style name="MyStyle">
    <item name="fontFamily">fonts/my_custom_font_regular.ttf</item>
</style>

<!-- To: -->

<style name="MyStyle">
    <item name="android:fontFamily">@font/my_custom_font_family</item>
</style>

<!-- -- -->

<style name="MyStyle">
    <item name="fontFamily">fonts/my_custom_font_italic.ttf</item>
</style>

<!-- To: -->

<style name="MyStyle">
    <item name="android:fontFamily">@font/my_custom_font_family</item>
    <item name="android:fontStyle">italic</item>
</style>

<!-- -- -->


<style name="MyStyle">
    <item name="fontFamily">fonts/my_custom_font_bold.ttf</item>
</style>

<!-- To: -->

<style name="MyStyle">
    <item name="android:fontFamily">@font/my_custom_font_family</item>
    <item name="android:fontStyle">bold</item>
</style>