RadioButton图标居中

<RadioGroup
    android:layout_width="match_parent"
    android:layout_height="57dp"
    android:orientation="horizontal"
    android:gravity="center_vertical">
    <RadioButton
        android:layout_weight="1"
        android:drawableTop="@drawable/reader_page_bg_rb_2_selector"
        android:button="@null"
        android:textSize="0sp"
        android:gravity="center"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
        ......
</RadioGroup>