Android spinner控件

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="app_name">spinner</string>
    <string name="action_settings">Settings</string>
    <string name="hello_world">Hello world!</string>
    <array name="city">
        <item>上海</item>
        <item>北京</item>
        <item>广州</item>
    </array>
</resources>

<Spinner
        android:id="@+id/spinner1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="22dp"
        android:layout_marginTop="49dp"
        android:entries="@array/city" />

package com.example.spinner;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.Toast;

public class MainActivity extends Activity {

    private Spinner sp;
    private Button btn;
    String cardNumber;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        sp=(Spinner) findViewById(R.id.spinner1);
        final String[] roles={"管理员","会员","游客"};
        ArrayAdapter<String> adapter=new ArrayAdapter<String>(this, android.R.layout.simple_dropdown_item_1line, android.R.id.text1, roles);
        sp.setAdapter(adapter);
        
        //Spinner的监听事件
        sp.setOnItemSelectedListener(new OnItemSelectedListener() {

            @Override
            public void onItemSelected(AdapterView<?> arg0, View arg1,
                    int arg2, long arg3) {
                cardNumber = MainActivity.this.getResources().getStringArray(R.array.city)[arg2];
                //cardNumber = roles[arg2];
                //设置显示当前选择的项
                //arg0.setVisibility(View.VISIBLE);
            }

            @Override
            public void onNothingSelected(AdapterView<?> arg0) {
                // TODO 自动生成的方法存根
                
            }
        });
        
        //Button的监听事件
        btn=(Button) findViewById(R.id.button1);
        btn.setOnClickListener(new OnClickListener() {
            
            @Override
            public void onClick(View arg0) {
                // TODO 自动生成的方法存根
                
                Toast.makeText(MainActivity.this, cardNumber, Toast.LENGTH_SHORT).show();
            }
        });
    }

    
}