Add a click effect for a button which is created by code

I have created a button with the code below, mybutton.xml:

<?xml version="1.0" encoding="utf-8"?> 
<shape xmlns:android="http://ift.tt/nIICcg"
    android:padding="10dp"
     android:shape="rectangle" >

     <solid android:color="#97ce68" />
     <stroke android:width="1dip"  />
     <corners
         android:bottomLeftRadius="6dp"
         android:bottomRightRadius="6dp"
         android:topLeftRadius="6dp"
         android:topRightRadius="6dp" />

 </shape>

I want to add a press effect for that button so I make the following code effect_button.xml :

    <?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://ift.tt/nIICcg">
    <item android:drawable="@drawable/img1" android:state_pressed="false" android:state_selected="false"/>
    <item android:drawable="@drawable/img2" android:state_pressed="true"/>

so how can I add the second xml file(effect_button.xml) to make it the background if I have already use this method with the first file in the stage of creation of the button(mybutton.xml):

Button myButton = new Button(this);
                myButton.setBackgroundDrawable(getResources().
                    getDrawable(R.drawable.
                        mybutton));