Android drawable xml Can't convert to color Exception for API 10

Question

In my app I define color attributes that I set in a custom theme:

res/values/attrs.xml

<resources>
    <attr name="bbColorPrimary" format="color|reference" />
</resources>

res/values/colors.xml

<resources>
    <color name="white">#ffffff</color>
</resources>

res/values/style.xml

<style name="MyStyle" parent="@style/Theme.AppCompat.NoActionBar">
    <item name="bbColorPrimary">@color/white</item>
</style>

res/drawable/background.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android" >
    <item android:state_pressed="true">
        <shape>
            <solid android:color="?attr/bbColorPrimary" />
        </shape>
    </item>
    <item>
        <shape>
            <solid android:color="@color/transparent" />
        </shape>
    </item>
</selector>

res/drawable/background.xml is set as the background of some button. The app crashes while inflating the res/drawable/background.xml file, with the following exception:

...
Caused by: java.lang.UnsupportedOperationException: Can't convert to color: type=0x2
            at android.content.res.TypedArray.getColor(TypedArray.java:326)
            at android.graphics.drawable.GradientDrawable.inflate(GradientDrawable.java:748)
            at android.graphics.drawable.Drawable.createFromXmlInner(Drawable.java:787)
            at android.graphics.drawable.StateListDrawable.inflate(StateListDrawable.java:172)
....

It works on API levels higher than 10. If I remove the ?attr/bbColorPrimary it works fine, although many other ?attr/.. calls are set in other resource files. I am not using any version-specific resource folders.

What am I doing wrong here?

Answer 1

I found an answer on SO, mentioning that ?attr/.. are not supported in xml drawables. See here: https://stackoverflow.com/a/13471695/169748

Apparently that is true at least for API <= 10.