question about change the colours of a button when clicked

My purpose is to change the color of a button when click and my codes are

<?xml version="1.0" encoding="utf-8"?>
selector xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- When selected, use grey -->
    <item android:drawable="@drawable/btn_askering_active" android:state_selected="true" />
    <!-- When not selected, use white-->
    item android:drawable="@drawable/btn_askering" />
</selector>

It works but if i make a small ch开发者_StackOverflowange like below :

xmlns:android="http://schemas.android.com/apk/res/android">
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- When not selected, use white-->
    item android:drawable="@drawable/btn_askering" />
    <!-- When selected, use grey -->
    item android:drawable="@drawable/btn_askering_active" android:state_selected="true" />
</selector>

It does not work anymore.... I need some help...Any comments are welcomed here.Thanks

---

I think you need to mention stats in selector like pressed or focused and change image accordingly. Here i have attached sample selector file,have a look and try accordingly.

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


    <item android:state_focused="true" android:state_pressed="false"
        android:drawable="@drawable/estimator_hover_new" />
    <item android:state_focused="true" android:state_pressed="true"
        android:drawable="@drawable/estimator_hover_new" />
    <item android:state_focused="false" android:state_pressed="true"
        android:drawable="@drawable/estimator_hover_new" />

    <item android:drawable="@drawable/estimator_new" />


</selector>

All The Best....