Android: Is it possible to use string/enum in drawable selector?

Question

Questions

Q1: Has anyone managed to get custom string/enum attribute working in xml selectors? I got a boolean attribute working by following [1], bu

Answer 1

Q1:

When you open the source-code of StateListDrawable.java, you can see this piece of code in the inflate method that reads the drawable xml selector: https://android.googlesource.com/platform/frameworks/base/+/refs/heads/master/graphics/java/android/graphics/drawable/StateListDrawable.java

        ...

        for (i = 0; i < numAttrs; i++) {
            final int stateResId = attrs.getAttributeNameResource(i);
            if (stateResId == 0) break;
            if (stateResId == com.android.internal.R.attr.drawable) {
                drawableRes = attrs.getAttributeResourceValue(i, 0);
            } else {
                states[j++] = attrs.getAttributeBooleanValue(i, false)
                        ? stateResId
                        : -stateResId;
            }
        }
        ...

attrs are the attributes of each element in the .

In this for-loop it gets the android:drawable, the various android:state_xxxx and custom app:xxxx attributes. All but the android:drawable attributes seem to be interpreted as booleans only: attrs.getAttributeBooleanValue(....) is called.

I think this is the answer, based on the source code:

You can only add custom boolean attributes to your xml, not any other type (including enums).

Q2:

I'm not sure why the state is merged only if it is specifically set to true. I would suspect the code should have looked like this instead:

private static final int[] MAKE_DARK_BG_SET     = {  R.attr.make_dark_background };
private static final int[] NOT_MAKE_DARK_BG_SET = { -R.attr.make_dark_background };
....
....
@Override
protected int[] onCreateDrawableState(int extraSpace) {
    Log.i(TAG, "onCreateDrawableState()");
    final int[] drawableState = super.onCreateDrawableState(extraSpace + 2);
    mergeDrawableStates(drawableState, mMakeDarkBg? MAKE_DARK_BG_SET : NOT_MAKE_DARK_BG_SET);
    //mergeDrawableStates(drawableState, STR_ATTR_ID);
    return drawableState;
}