ExpandableListView的下拉图标替换

ExpandableListView的小图标有个状态，一个是不点击的情况，一个是点击后展开的情况，用xml配置如下：

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
           <item android:state_expanded="true" android:drawable="@drawable/narrow_select" />
           <item android:drawable="@drawable/narrow" />
</selector>

Java的代码如下：

ExpandableListView listView = getExpandableListView();

listView.setGroupIndicator(this.getResources().getDrawable(R.drawable.group_icon_selector));