RadioButton背景图片怎么样根据宽度按比扩大与缩小

<RadioButton
   android:id="@+id/menu_tab_more"
                android:layout_width="0dip"
                android:layout_height="wrap_content"
                 android:layout_weight="1.0"
                android:background="@drawable/menu_more_btn_bg"
                android:button="@null"
                android:gravity="center"
                android:scaleType="centerInside"
                android:tag="more" />