action bar 不显示图标问题

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    tools:context="com.example.actionbartest.MainActivity" >
    
    <item  
        android:id="@+id/action_compose"  
        android:icon="@drawable/ic_action_compose"  
        android:showAsAction="ifRoom"  
        android:title="@string/action_compose"/>  
        
    <item  
        android:id="@+id/action_delete"  
        android:icon="@drawable/ic_action_delete"  
        android:showAsAction="always"  
        android:title="@string/action_delete"/>  
    
    <item
        android:id="@+id/action_settings"
        android:icon="@drawable/ic_action_setting"
        android:orderInCategory="100"
        android:title="@string/action_settings"
           android:showAsAction="never"/>

</menu>