Android layout xml: center layout, element width portion, numbers only input for EditText

The layout xml file below is a RelativeLayout containing a LinearLayout which contains a EditText, a Button, and a TextView.

The LinearLayout is centered in the screen by android:layout_centerInParent=”true”, and this only works if it is inside the RelativeLayout.
EditText only accepts positive numbers and negative numbers by android:inputType=”numberDecimal|numberSigned”.
EditText, Button and TextView are lined up on the same line because they are in the LinearLayout, and the LinearLayout says android:orientation=”horizontal”.
The EditText will occupy 6/10 of the total width of the LinearLayout because its layout_weight is set to 6 and the layout_width is set to 0dp.
The Button will occupy 3/10 of the total width of the LinearLayout because its layout_weight is set to 3 and the layout_width is set to 0dp.
The TextView, will occupy 1/10 of the total width of the LinearLayout because its layout_weight is set to 1 and the layout_width is set to 0dp.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <LinearLayout 
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:layout_centerInParent="true">
	    <EditText 
	        android:id="@+id/number_input"
	        android:layout_weight="6"
	        android:layout_width="0dp"
	        android:layout_height="wrap_content"
	        android:inputType="numberDecimal|numberSigned"
	        android:maxLength="15"
	        android:hint="Enter a number" />

	    <Button
	        android:id="@+id/submit_button"
	        android:layout_weight="3"
	        android:layout_width="0dp"
	        android:layout_height="wrap_content"
	        android:text="Submit" />
	    
	    <TextView
	        android:id="@+id/smiley_face"
	        android:layout_weight="1"
	        android:layout_width="0dp"
	        android:layout_height="wrap_content"
	        android:text=":)"
	        />

	</LinearLayout>

</RelativeLayout>