Font resources enible developers to incorporate custom typefaces into user interfaces. They can be stored locally within the application bundle or fetched remotely via a provider system.

Local Packaging

Appplications may package fonts directly inside the APK. These resources compile into the R class and become accessible as standard resource references. Supported formats include TTF, TTC, OTF, or an XML descriptor file.

Placement:

• Directory: res/font/
• Filename: <name>.ttf, .otf, or .xml
• Reference: Use @[package:]font/<resource_name> in layout XML.

Descriptor Syntax: When using an XML descriptor to manage multiple variants (e.g., bold, italic), define a root <font-family> element. Individual styles use <font> tags to override header metadata.

<!-- res/font/app_typeface.xml -->
<font-family xmlns:android="http://schemas.android.com/apk/res/android">
    <font
        android:fontStyle="normal"
        android:fontWeight="400"
        android:font="@font/regular_weight" />
    
    <font
        android:fontStyle="italic"
        android:fontWeight="700"
        android:font="@font/bold_variant" />
</font-family>

Key Attributes:

• android:font: Resource ID pointing to the binary font file.
• android:fontStyle: Defines style (normal, italic). Defaults to font header if omitted.
• android:fontWeight: Weight value between 100 and 900 (multiples of 100).

Usage Example:

<!-- res/layout/activity_main.xml -->
<TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:fontFamily="@font/app_typeface"
    android:text="Local Custom Typeface" />

Remote Downloadable Fonts

Alternatively, fonts can be retrieved at runtime from a third-party service. This approach minimizes APK size and allows updates without redistributing the app.

Provider Configuration: Define the lookup logic in res/font/download_font.xml. This requires specifying the authority, package, query, and certificate chain for the source.

<!-- res/font/google_lato.xml -->
<font-family xmlns:android="http://schemas.android.com/apk/res/android"
    android:fontProviderAuthority="com.google.android.gms.fonts"
    android:fontProviderPackage="com.google.android.gms"
    android:fontProviderQuery="Lato"
    android:fontProviderCerts="@array/provider_certs" />

Required Attirbutes:

• android:fontProviderAuthority: Service identifier for the font source.
• android:fontProviderPackage: Package name containing the provider.
• android:fontProviderQuery: Search string for the specific font name.
• android:fontProviderCerts: Array of SHA256 hashes verifying the provider's signature.

Certificate Storage: Hashes must be defined in an array resource:

<!-- res/values/array.xml -->
<resources>
    <string-array name="provider_certs">
        <item>SHA256_CERT_HASH...</item>
    </string-array>
</resources>

Runtime Application: The usage syntax mirrors local fonts:

<!-- res/layout/detail_view.xml -->
<TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:fontFamily="@font/google_lato"
    android:text="Streaming from Provider" />