Is it possible to reference attributes from styles.xml file?

Question

I want to give the user the possibility to switch the colors skin of my entire application. I mean to switch the style of some custom views of the app dynamically when the user presses a button of the screen. I know that if you call Activity.setTheme() before onCreate() method, you can change the theme of the app dynamically, but normal Views (for example, NavigationView) with custom styles applied on their xml layout, do not have setTheme or setStyle methods, so it is does not appear possible to change their style dynamically.

I think that my objective would be possible referencing colors declared in an AppTheme declared inside styles.xml file. I mean, i can have two AppThemes declared, each one with one set of colors, and then, in the custom styles declared for the custom views, reference the colors. Something like this:

<resources>
    <style name="AppTheme" parent="Theme.AppCompat">
        <item name="customColor">#111111</item>
    </style>

    <style name="AppTheme.AnotherColor" parent="Theme.AppCompat">
        <item name="customColor">#222222</item>
    </style>

    <style name="CustomActionBar">
        <!-- title text color -->
        <item name="android:textColorPrimary">@styles/customColor</item>
    </style>
</resources>

So, by default, the custom Color declared on my "AppTheme" will be applied by default, using color 111111. But when I change the theme of my app using setTheme(R.styles.AppTheme_AnotherColor) the color applied will be 222222. If this would be possible it would be perfect! but it is not possible or I don't know how to access to a color declared inside a style directly from another style of the same styles.xml file. I mean that @styles/customColor is not correct and I don't know how to access that color.

How can this be achieved?

Custom attributes are referenced using ?attr/customAttributeName, so in your case you need to put ?attr/customColor in your CustomActionBar theme. — TR4Android
– TR4Android, Commented Aug 15, 2016 at 17:51
@TR4Android does not find the atribute. Test it please. You should reference it from another <style> tag. Something is wrong because can't find it. — NullPointerException
– NullPointerException, Commented Aug 15, 2016 at 18:00
Have you defined it in your attrs.xml file? Each custom attribute needs to be defined there so it can be found. Put something like <resources><attr name="customColor" format="color"/></resources> in that file. — TR4Android
– TR4Android, Commented Aug 15, 2016 at 18:05
@TR4Android And will I have the possibility to change it's value in my AppTheme and AppTheme.AnotherColor dinamically? — NullPointerException
– NullPointerException, Commented Aug 15, 2016 at 18:06
Yes, I've made it work in one of my apps. Themes and styles on Android can be at perky at times though... — TR4Android
– TR4Android, Commented Aug 15, 2016 at 18:07

TR4Android · Accepted Answer · 2016-08-15 20:59:42Z

9

Yes, it is definitely possible to add custom attributes and colors to the themes. For this you need to:

Define your custom attribute in your res/values/attrs.xml file:

<resources>
    <attr name="customColor" format="color" />
</resources>

Define the attribute's value in your themes:

<style name="AppTheme" parent="Theme.AppCompat">
    <item name="customColor">#111111</item>
</style>

<style name="AppTheme.AnotherColor" parent="Theme.AppCompat">
    <item name="customColor">#222222</item>
</style>

Use your custom attribute in your styles:

<style name="CustomActionBar">
    <!-- title text color -->
    <item name="android:textColorPrimary">?attr/customColor</item>
</style>

edited Aug 15, 2016 at 20:59

answered Aug 15, 2016 at 20:43

TR4Android

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4 Comments

NullPointerException Over a year ago

thank you so much. Is it possible to write the value of the custom xml attribute (created in attrs.xml) with java code?

TR4Android Over a year ago

Not easily. Android themes and styles are really one of the most inflexible things. You can find a few hints here.

NullPointerException Over a year ago

TR4Android it is possible to use this with a widget color¿? Widget does not have theme, so can't set the value of the attr setting the theme on the widget... must be other way

TR4Android Over a year ago

Unfortunately, I have no experience with widgets, but you could try just using something like android:background="?attr/customColor".

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