How to extend an Android button and use an xml layout file

I'm trying to extend the android button class and have it use an xml layout file.

The reason I want to use an xml layout file is that my button needs to use a style and as far as I know, there isn't a way to set style programatically.

public class BuyButton extends Button { ... }

<?xml version="1.0" encoding="utf-8"?>  
 <Button 
     xmlns:android="http://schemas.android.com/apk/res/android" 
     style="@style/customButton"
 />
 

so that I can call:

new BuyButton(activity);
 

and have it create a button that has the style applied to it.

(I'm also open to other ways of getting the same result)

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