How to set the absolute position of an image or button so that it is consistent across multiple screen sizes?

After searching for a few hours, I was unable to find the exact answer to my situation. I'm currently using a RelativeLayout and all I have is a background image and a button. The problem I'm having is placing the button in the exact location I want it to be (a little offset from the center).

My first attempt was to modify the layout_margins of the button. While this worked for the current emulator I was working with (3.7in WVGA), the positioning of the button was slightly/way off for a different screen size (such as 3.2in HVGA).

I then attempted to modify the padding of the parent layout but got the same issue. My XML looks like this:

<?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="fill_parent"
                android:paddingLeft="98dip" android:paddingBottom="68dip" android:background="@drawable/background">
    <Button android:id="@+id/starttimer" 
            android:background="@drawable/button" 
            android:layout_width="wrap_content" android:clickable="true" android:layout_height="wrap_content" android:layout_alignParentBottom="true"/>
</RelativeLayout>

Please let me know if I'm completely 开发者_如何学编程off with my approach. It seems like an extremely simple problem, and I'm bummed out that it's taken me so long to try to get it. Thanks for any help!

I take it that you want to center the button on the bottom of the parent with a little offset, try layout_centerHorizontal then add your preferred margin.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:layout_width="fill_parent"
                android:layout_height="fill_parent"
                android:paddingLeft="98dip" android:paddingBottom="68dip" android:background="@drawable/background">
    <Button android:id="@+id/starttimer" 
            android:background="@drawable/button" 
            android:layout_width="wrap_content" android:clickable="true" android:layout_height="wrap_content" android:layout_alignParentBottom="true" android:layout_centerHorizontal="true" android_marginLeft="5dp"/>
</RelativeLayout>

Absolute Layout is used for absolute positions of the control.