Is there any possibility to show a spinning progress bar in a button? e.g. as background drawable?
Yes.
You can create an AnimationDrawable, as described here, and then use the drawableLeft
tag (for example) in your button's XML. like so:
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="@drawable/your_background_drawable_resource"
android:drawableLeft="@drawable/your_animation_drawable_resource"
android:text="@string/your_text_res">
</Button>