Android Set Button Background Transparent (maintain touch/click animation/ripple effect)

Using android:background="?android:attr/selectableItemBackground" would make background transparent while maintaining touch animation.

<Button
    android:text="Test"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="?android:attr/selectableItemBackground"
     />

Using android:background="@android:color/transparent" would make background transparent with no touch animation.

NOTE: If you are using Material theme, android:background would not work. Use android.widget.Button instead..