Android XML: Center ImageButtons Regardless of Screen Orientation

Question

I'm attempting to center my image buttons side by side in a row, but centered in the screen as well - I tried to accomplish this using:

Currently they are appearing centered horizontally and vertically as I would like - how can I get them to align in a row while keeping them centered in the screen (regardless of horizontal or vertical screen rotation).

Current:

Desired:

<?xml version="1.0" encoding="UTF-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/layout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <ImageButton
        android:id="@+id/imageButton3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:src="@drawable/photos" />

    <ImageButton
        android:id="@+id/imageButton2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:src="@drawable/audio" />

    <ImageButton
        android:id="@+id/imageButton1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:src="@drawable/written" />

    <ImageButton
        android:id="@+id/imageButton4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:src="@drawable/video" />

</RelativeLayout>

Answer 1

<LinearLayout
    android:id="@+id/linearLayout1"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_centerVertical="true"
    android:weightSum="1" >

    <View
        android:id="@+id/view1"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_weight="0.3" />

    <ImageButton
        android:id="@+id/imageButton3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="0.1"
        android:src="@drawable/photos" />

    <ImageButton
        android:id="@+id/imageButton2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="0.1"
        android:src="@drawable/audio" />

    <ImageButton
        android:id="@+id/imageButton1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="0.1"
        android:src="@drawable/written" />

    <ImageButton
        android:id="@+id/imageButton4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="0.1"
        android:src="@drawable/video" />

    <View
        android:id="@+id/view1"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_weight="0.3" />
</LinearLayout>