android 下拉菜单Spinner

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

    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="25sp"
        android:textColor="#ff0000"
        />

    <Spinner
        android:id="@+id/spinner"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

package com.example.hello;

import java.util.ArrayList;
import java.util.List;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.TextView;


public class MainActivity extends ActionBarActivity implements OnItemSelectedListener{

    private TextView textView;
    private Spinner spinner;
    private List<String> list;
    private ArrayAdapter<String> adapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        textView = (TextView) findViewById(R.id.textView);
        textView.setText("您选择的城市是：");
        
        spinner = (Spinner) findViewById(R.id.spinner);
        
        list = new ArrayList<String>();
        list.add("北京");
        list.add("上海");
        list.add("广州");
        list.add("深圳");
        
        adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item,list);
        adapter.setDropDownViewResource(android.R.layout.simple_dropdown_item_1line);
        spinner.setAdapter(adapter);
        
        spinner.setOnItemSelectedListener(this);
    }
    @Override
    public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2,long arg3) {
        String cityName = adapter.getItem(arg2);
        //String city = list.get(arg2);
        textView.setText("您选择的城市是："+cityName);
    }
    @Override
    public void onNothingSelected(AdapterView<?> arg0) {
        // TODO Auto-generated method stub
        
    }
}