Android selector 无效的问题

这几天做项目，用到背景选择器，无论怎么弄， 都没有效果，找了很多资料都没有找到，样式是这样的

<?xml version="1.0" encoding="UTF-8"?> 
<selector xmlns:android="http://schemas.android.com/apk/res/android"> 
　　 <item android:drawable="@drawable/title_new_normal"/> 
    <item android:drawable="@drawable/title_new_selected" android:state_focused="true"/> 
    <item android:drawable="@drawable/title_new_selected" android:state_selected="true"/> 
    <item android:drawable="@drawable/title_new_selected" android:state_pressed="true"/> 
    <item android:drawable="@drawable/title_new_selected" android:state_enabled="false"/>     
  
</selector>

后来偶然间，把默认的放在最下面，就好用啦

<?xml version="1.0" encoding="UTF-8"?> 
<selector xmlns:android="http://schemas.android.com/apk/res/android"> 
  
    <item android:drawable="@drawable/title_new_selected" android:state_focused="true"/> 
    <item android:drawable="@drawable/title_new_selected" android:state_selected="true"/> 
    <item android:drawable="@drawable/title_new_selected" android:state_pressed="true"/> 
    <item android:drawable="@drawable/title_new_selected" android:state_enabled="false"/> 
    <item android:drawable="@drawable/title_new_normal"/> 
  
</selector>