Android开发 更改返回button的图标

actionBar = getActionBar();
        actionBar.setDisplayHomeAsUpEnabled(true);

        actionBar.setHomeAsUpIndicator(R.drawable.back);

<style name="style_titlebar_normal" parent="Theme.AppCompat.Light">
 
      	<item name="android:homeAsUpIndicator">@drawable/back</item> <!--返回icon-->

    </style>  

<activity
            android:name="com.logic.activity.Activity1"
            android:theme="@style/style_titlebar_normal"
            >
        </activity>