Button - Thay đổi màu khi chọn button

- Selector_btn.xml : 

<?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/custom_button_keyboard"/>
<item android:drawable="@drawable/custom_button_keyboard_click"/>
</selector>

- Shape_btn_normal.xml : 

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" >
    <solid android:color="#fff"/>
</shape>

- Shape_btn_selected.xml :

<?xml version="1.0" encoding="utf-8"?>

<shape xmlns:android="http://schemas.android.com/apk/res/android" >

    <solid android:color="#ff0000"/>

</shape>