Relative Layout. Between 2 items

You will need to add another layout so that the button will be exactly in the middle. For example, add this to your layout:

<FrameLayout
    android:layout_width="wrap_content"
    android:layout_height="fill_parent"
    android:layout_above="@+id/button_bottom"
    android:layout_alignLeft="@+id/button_center"
    android:layout_alignRight="@+id/button_center"
    android:layout_below="@id/button_center" >
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="new" />
</FrameLayout>