Android tabhost让选中项加上背景图

现用了一tabhost，选中某选项时，会跟上一背景图，实现代码如下
tab_indicator.xml

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

</selector>