change image in button while is pressed

i have this code

<?xml version="1.0" encoding="utf-8"?>
 <selector xmlns:android="http://schemas.android.com/apk/res/android">
     <item android:state_pressed="true"
           android:drawable="@drawable/fundo" /> <!-- pressed -->
     <item android:drawable="@drawable/fundo2" /> <!-- default -->
 </selector>

in other file

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >


    <Button android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:background="@drawable/btn"
         />

</FrameLayout>

and in the class

 @Override
    public boolean onTouch(View v, MotionEvent event) {

        switch (event.getAction()) {

        case MotionEvent.ACTION_DOWN:
            mp.setLooping(true);
            mp.start();
            return true;

        case MotionEvent.ACTIO开发者_开发问答N_UP:
            mp.pause();
            return true;

        }

        return true;

    }

i don't know why, when the button is pressed the image don't change, what is the reason?

thanks!!

Instead of android:background="@drawable/btn" please use android:src="@drawable/btn".

It Works for me .

Inside ur xml, for the button background give ur selector xml file name.

<Button android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:background="@drawable/ur state change xml file name"
/>

You can use setBackgroundResource(ResId) for the change on button u can write this in the OnClick() method of the Button.