Android EditText and Button on same line

Does it have to be Relative Layout?
I would suggest the following: set EditText layout_width to fill_parent and its layout_weight to 1, something like this:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_height="wrap_content" android:orientation="horizontal"
android:layout_width="fill_parent">
<EditText android:text="@+id/EditText01" 
    android:id="@+id/EditText01"
    android:layout_height="wrap_content" 
    android:layout_weight="1"
    android:layout_width="fill_parent">
</EditText>
<Button android:text="@+id/Button01" 
    android:id="@+id/Button01"
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content">
</Button>

</LinearLayout>