```
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <RelativeLayout
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true" >

    <Button
        android:id="@+id/bb"
        android:layout_weight="1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:drawableLeft="@drawable/bb"
        android:drawablePadding="5dp"
        android:text="bb" />

    <Button
        android:id="@+id/cc"
        android:layout_weight="1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/bb"
        android:drawableLeft="@drawable/cc"
        android:drawablePadding="5dp"
        android:text="cc" />

    </RelativeLayout>

</RelativeLayout>

```

there should be two buttons in the screen with same width in the center. but there is nothing but blank screen x.x
I'm not that new in developing android, but sometimes I miss little details which give me a lot of headache. sorry for disturbing