android - How do I put a button A under button B such that the left side of A is vertically aligned with the center of B? -

how position button starts vertically aligned middle of button above it? size of upper button may vary screen screen.

thanks in advance,

is need?

<?xml version="1.0" encoding="utf-8"?> <linearlayout xmlns:android="http://schemas.android.com/apk/res/android"               android:layout_width="match_parent"               android:layout_height="match_parent"               android:gravity="center_horizontal"               android:orientation="vertical">      <button         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="first button"/>      <linearlayout         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_weight="2"         android:orientation="horizontal">          <button             android:layout_width="0dp"             android:layout_height="wrap_content"             android:layout_weight="1"             android:visibility="invisible"/>          <button             android:layout_width="0dp"             android:layout_height="wrap_content"             android:layout_weight="1"             android:text="second"/>     </linearlayout>  </linearlayout>