[android] How to align linearlayout to vertical center?

Use layout_gravity instead of gravity. layout_gravity tells the parent where it should be positioned, and gravity tells its child where they should be positioned.

<LinearLayout
    android:id="@+id/groupNumbers"
    android:orientation="horizontal"
    android:layout_gravity="center_vertical"
    android:layout_weight="0.7"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">