在layout-land中定义的xml布局没有出现在android应用程序中

知道为什么吗？

谢谢

更新 ：

活动代码：

public class ACENewsFeedActivity extends ListActivity {

    // Progress Dialog
    private ProgressDialog pDialog;

    // Array list for list view
    ArrayList<HashMap<String,String>> rssItemList = new ArrayList<HashMap<String,String>>();

    RSSParser rssParser = new RSSParser();

    List<RSSItem> rssItems = new ArrayList<RSSItem>();

    RssFeed rssFeed;

    private static String TAG_TITLE = "title";
    private static String TAG_LINK = "link";
    private static String TAG_DESRIPTION = "description";
    private static String TAG_PUB_DATE = "pubDate";
    //private static String TAG_GUID = "guid"; // not used

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.rss_item_list);

        /**
         * Calling a backgroung thread will loads recent articles of a website
         * @param rss url of website
         * */
        new loadRSSFeedItems().execute();
       }

       ....
}

横向模式下的XMl布局：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/layoutHeader"
    android:layout_width="fill_parent"
    android:layout_height="50dip"
    android:layout_alignParentTop="true"
    android:background="@layout/header_gradient"
    android:orientation="horizontal">

    <!-- Logo -->

    <!-- Refresh -->


    <!-- Plus Button -->

    <ImageButton
        android:id="@+id/btnAddSite"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_marginRight="5dip"
        android:background="@null"
        android:src="@drawable/plus"
        android:layout_centerVertical="true" />

    <ImageView
        android:id="@+id/logo"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_centerVertical="true"
        android:src="@drawable/logo" />

    <ImageView
        android:id="@+id/refreshList"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:src="@drawable/refresh" />

</RelativeLayout>