Android级联菜单的实现方法

package mldn.lxd.OnItemSlectListerner;
import android.R.anim;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.SpinnerAdapter;

public class OnItemSelectListernerActivity extends Activity {
   
    private Spinner spinnerTopProvince =  null;
    private Spinner spinnerSubCitys =  null;
    private  String[][] citys ={{ "朝阳" ,   "阳台" ,   "紫金" ,   "海淀"},
         {  "抚顺" ,   "大连"  ,  "青岛" ,  "烟台"},
         {"济南" ,  "菏泽" , "威海", "单县" },
          {"开封" ,  "安阳" ,  "洛阳" ,  "南阳"}};
   private ArrayAdapter<CharSequence> arrayAdapter = null;
                     
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {

       super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        spinnerTopProvince=(Spinner)      super.findViewById(R.id.idTopSpinner);
        spinnerSubCitys=(Spinner)       super.findViewById(R.id.idSubSpinner);
        spinnerTopProvince.setOnItemSelectedListener(new myItemSelectedLisener());
           
    }
    
    private final class myItemSelectedLisener  implements OnItemSelectedListener
    {
       
      @Override
      public void onItemSelected(AdapterView<?> parent, View view, int position, long id) 
      {
         OnItemSelectListernerActivity.this.arrayAdapter = 
               new ArrayAdapter<CharSequence>   (OnItemSelectListernerActivity.this, 
               android.R.layout.simple_spinner_item,OnItemSelectListernerActivity.this.citys[position]);
         spinnerSubCitys.setAdapter(arrayAdapter);
      }

      @Override
      public void onNothingSelected(AdapterView<?> arg0)
      {
         // TODO Auto-generated method stub
         
      }
       
    }
}

<?xml version= "1.0" encoding= "utf-8"?>
<LinearLayout xmlns:android= "http://schemas.android.com/apk/res/android"
    android:layout_width= "fill_parent"
    android:layout_height= "fill_parent"
    android:orientation= "vertical" >

    <TextView
        android:layout_width= "fill_parent"
        android:layout_height= "wrap_content"
        android:text= "@string/hello"  />
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="horizontal" >
       <Spinner 
           android:entries="@array/LoveProvice"
           android:id="@+id/idTopSpinner"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           />
       
       <Spinner 
           android:id="@+id/idSubSpinner"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           />
   
      </LinearLayout>

</LinearLayout>