Theming and Styling XML UIs for Android Apps

In Android development, a consistent and attractive user interface is crucial for providing a good user experience. Theming and styling are essential techniques for achieving this consistency and enhancing the visual appeal of your app. This guide covers theming and styling for XML-based UIs in Android apps.

What is Theming in Android?

Theming in Android refers to applying a consistent set of visual attributes to your entire app. A theme includes settings for colors, fonts, and other stylistic elements. It ensures uniformity and aligns your app with your brand’s visual identity.

What is Styling in Android?

Styling, on the other hand, focuses on applying visual attributes to individual views or groups of views. Styles are reusable sets of properties that can be applied to UI components to maintain consistency and reduce redundancy.

Why Use Theming and Styling?

• Consistency: Ensures a uniform look and feel across your app.
• Maintainability: Simplifies the process of updating visual attributes.
• Reusability: Allows you to reuse styles and themes across different parts of your app.
• Reduced Redundancy: Minimizes duplication of visual property definitions.

How to Implement Theming and Styling for XML UIs

To implement theming and styling in Android XML UIs, follow these steps:

Step 1: Define Your Theme

Themes are defined in the res/values/themes.xml file. Create or modify this file to define your app’s theme. For example:

<resources xmlns:tools="http://schemas.android.com/tools">
    <!-- Base application theme. -->
    <style name="Theme.MyApp" parent="Theme.MaterialComponents.DayNight.DarkActionBar">
        <!-- Primary brand color. -->
        <item name="colorPrimary">@color/purple_500</item>
        <item name="colorPrimaryVariant">@color/purple_700</item>
        <item name="colorOnPrimary">@color/white</item>
        <!-- Secondary brand color. -->
        <item name="colorSecondary">@color/teal_200</item>
        <item name="colorSecondaryVariant">@color/teal_700</item>
        <item name="colorOnSecondary">@color/black</item>
        <!-- Status bar color. -->
        <item name="android:statusBarColor" tools:targetApi="l">?attr/colorPrimaryVariant</item>
    </style>
</resources>

This defines a basic theme inheriting from Theme.MaterialComponents.DayNight.DarkActionBar and sets various color attributes.

Step 2: Apply the Theme to Your App

To apply the theme to your entire application, modify the android:theme attribute in the <application> tag in your AndroidManifest.xml file:

<application
    android:label="@string/app_name"
    android:theme="@style/Theme.MyApp">
    <!-- Activities, Services, etc. -->
</application>

Step 3: Define Styles

Styles are defined in the res/values/styles.xml file (or create one if it doesn’t exist). Here’s an example of defining a style for a TextView:

<resources>
    <style name="MyTextViewStyle">
        <item name="android:textSize">16sp</item>
        <item name="android:textColor">@color/black</item>
        <item name="android:fontFamily">sans-serif</item>
    </style>
</resources>

Step 4: Apply Styles to Views

Apply the style to a view in your layout XML using the style attribute:

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Hello, World!"
    style="@style/MyTextViewStyle"/>

Step 5: Theme-Aware Attributes

Use theme-aware attributes to ensure your views adapt to the current theme. For example, use ?attr/colorPrimary instead of hardcoding a color value:

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textColor="?attr/colorPrimary"
    android:text="Using Theme Color"/>

Example: Customizing Button Styles

Let’s create a custom style for buttons that changes the background color and text color:

<!-- res/values/styles.xml -->
<resources>
    <style name="MyButtonStyle" parent="Widget.MaterialComponents.Button">
        <item name="backgroundTint">@color/my_custom_color</item>
        <item name="android:textColor">@color/white</item>
        <item name="android:textSize">18sp</item>
        <item name="android:padding">12dp</item>
    </style>
</resources>

Apply this style to your button:

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Click Me"
    style="@style/MyButtonStyle"/>

Example: Creating a DayNight Theme

To support both light and dark themes (DayNight), you’ll need to create a values-night directory in your res directory.

Step 1: Define Night Theme

In res/values-night/themes.xml:

<resources xmlns:tools="http://schemas.android.com/tools">
    <!-- Dark variant of the application theme. -->
    <style name="Theme.MyApp" parent="Theme.MaterialComponents.DayNight.DarkActionBar">
        <!-- Primary brand color. -->
        <item name="colorPrimary">@color/purple_200</item>
        <item name="colorPrimaryVariant">@color/purple_700</item>
        <item name="colorOnPrimary">@color/black</item>
        <!-- Secondary brand color. -->
        <item name="colorSecondary">@color/teal_200</item>
        <item name="colorSecondaryVariant">@color/teal_200</item>
        <item name="colorOnSecondary">@color/black</item>
        <!-- Status bar color. -->
        <item name="android:statusBarColor" tools:targetApi="l">?attr/colorPrimaryVariant</item>
    </style>
</resources>

Here, we override the colorPrimary to use @color/purple_200 for the dark theme.

Step 2: Color Definitions

Make sure you have different color definitions for the night mode. For example, in res/values/colors.xml:

<resources>
    <color name="purple_200">#FFBB86FC</color>
    <color name="purple_500">#FF6200EE</color>
    <color name="purple_700">#FF3700B3</color>
    <color name="teal_200">#FF03DAC5</color>
    <color name="black">#FF000000</color>
    <color name="white">#FFFFFFFF</color>
    <color name="my_custom_color">#FF009688</color>
</resources>

And in res/values-night/colors.xml:

<resources>
    <color name="purple_200">#FFBB86FC</color>
    <color name="purple_500">#FF6200EE</color>
    <color name="purple_700">#FF3700B3</color>
    <color name="teal_200">#FF03DAC5</color>
    <color name="black">#FF000000</color>
    <color name="white">#FFFFFFFF</color>
    <color name="my_custom_color">#FF3F51B5</color>
</resources>

By using DayNight theme and theme-aware attributes, your app will automatically switch between the light and dark themes based on the system settings.

Conclusion

Theming and styling are vital for creating visually appealing and consistent Android apps. By defining themes and styles, you can ensure your app aligns with your brand and provides a great user experience. Leverage theme-aware attributes and DayNight support for apps that adapt to system-wide theme changes. Properly implementing these techniques significantly enhances the maintainability and visual harmony of your application.