Question

I have a simple problem. I’d like to provide multiple themes for my UI that a user can switch between

The problem is that I can use a theme that styles primitive UI classes, or I can use a style directly on an XML layout element, but I can’t define a style that will then change based on the theme I have applied. Not all of the styling I want to do is based on the primitive type.

I would say that what I want to do is similar to using a CSS selector to style a class or ID, but themes only allow you to style an element name.

---

The best I can do right now is have a base style that inherits from EITHER of the actual styles I’ve built, as below:

My res/values/style.xml

// All styles have to be subclassed here to be made generic, and only one
// can be displayed at a time. Essentially, I'm doing the same thing as setting
// a theme does, but for styles. If I have 50 styles, I have to have 50 of
// these for each theme, and that's not DRY at all!
<style name="MyHeaderStyle" parent="MyHeaderStyle.Default"/>
<!--
    <style name="MyHeaderStyle" parent="MyHeaderStyle.Textures"/>
-->

<style name="MyHeaderStyle.Default">
    <item name="android:background">@android:color/background_dark</item>
</style>

<style name="MyHeaderStyle.Textures">
    <item name="android:background">@drawable/header_texture</item>
</style>

Usage in my layout.xml:

<!-- Note that I can't use a theme here, because I only want to style a
     SPECIFIC element -->
<LinearLayout android:layout_width="fill_parent"
              android:layout_height="wrap_content"
              style="@style/MyHeaderStyle"
              android:gravity="center">
</LinearLayout>

Answer 1

Try this method:

1) Define your own res/values/attrs.xml file:

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <declare-styleable name="AppTheme">
        <attr name="myLinearLayoutStyle" format="reference" />
    </declare-styleable>

</resources>

2) Assign the above attr to you LinearLayout

<LinearLayout android:layout_width="fill_parent"
              android:layout_height="wrap_content"
              style="?attr/myLinearLayoutStyle"
              android:gravity="center">
</LinearLayout>

3) Assign a concrete style to this attr:

<style name="AppLightTheme" parent="android:Theme.Holo.Light">
    <item name="@attr/myLinearLayoutStyle">@style/lightBackground</item>
</style>

<style name="AppTheme" parent="android:Theme.Holo">
    <item name="@attr/myLinearLayoutStyle">@style/darkBackground</item>
</style>

<style name="lightBackground">
    <item name="android:background">#D1CBF5</item>
</style>

<style name="darkBackground">
    <item name="android:background">#351BE0</item>
</style>

Hope I understood correctly your question.