Q: How to align a widget at bottom_vertical | center_horizontal with RelativeLayout This is the page:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:gravity="center_horizontal"
              android:layout_width="fill_parent"
              android:layout_height="fill_parent"
              android:clickable="true">

              <ImageView
                  android:id="@+id/imageView1"
                  android:contentDescription="@string/Image_BG_desrp"
                  android:layout_width="match_parent"
                  android:layout_height="match_parent"
                  android:scaleType="centerCrop"
                  android:src="@drawable/background_main" />
              <TextView
                  android:id="@+id/a1"
                  android:layout_width="wrap_content"
                  android:layout_height="wrap_content"
                  android:layout_marginTop="15dp"
                  android:text="@string/1"
                  android:layout_centerHorizontal="true"
                  android:textColor="#FFFFFF"
                  android:textStyle="bold"
                  android:textSize="18sp"
                  android:focusable="true"
                  android:focusableInTouchMode="true" />
              <TextView
                  android:id="@+id/a2"
                  android:layout_width="wrap_content"
                  android:layout_height="wrap_content"
                  android:layout_marginTop="30dp"
                  android:text="@string/2"
                  android:layout_centerHorizontal="true"
                  android:textColor="#FFFFFF"
                  android:textStyle="bold"
                  android:textSize="28sp"
                  android:focusable="true"
                  android:focusableInTouchMode="true" />
              <TextView
                  android:id="@+id/a3"
                  android:layout_width="wrap_content"
                  android:layout_height="wrap_content"
                  android:layout_marginTop="60dp"
                  android:layout_centerHorizontal="true"
                  android:text="@string/3"
                  android:textColor="#FFFFFF"
                  android:textStyle="bold"
                  android:textSize="18sp" />

I want to put this button at bottom_vertical | center_horizontal (center of bottom) page:
<Button
    android:id="@+id/btn_xml"
    android:layout_width="85dp"
    android:layout_height="35dp"
    android:gravity="center"
    android:text="@string/Continue"
    android:textColor="#FFFFFF"
    android:textSize="16dp"/>

I put this Button in LinearLayout and use Margin-Top and use some dimension, but with different screen-size it's gonna be problem.
Is there any way to align with RelativeLayout without giving any dimension.
Note: I have to use RelativeLayout!! 

A: Add This in Button Tag:
    android:layout_alignParentBottom="true"
    android:layout_centerHorizontal="true"


A: Add 
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"

to your Button and it will be centered in the bottom of the screen.

A: try this one  
    <Button
        android:id="@+id/btn_xml"
        android:layout_width="85dp"
        android:layout_height="35dp"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:gravity="center"
        android:text="@string/Continue"
        android:textColor="#FFFFFF"
        android:textSize="16dp" />

