Spinner实现列表下拉功能

public class MainActivity extends AppCompatActivity
        implements AdapterView.OnItemSelectedListener { 
private TextView textview;
    private Spinner spinner;
    private List<String> list;
    private ArrayAdapter adapter;
    @Override
    protected void onCreate(Bundle savedInstanceState)  {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textview=(TextView) findViewById(R.id.textView);
        spinner=(Spinner)findViewById(R.id.sPinner);
        list=new ArrayList<String>();
  //1.数据源
        list.add("北京");
        list.add("上海");
        list.add("广州");
        list.add("美国");
 //2.适配器
        adapter=new ArrayAdapter(this,android.R.layout.simple_spinner_item,list);
//3.adapter设置一个下拉列表样式
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
//4.装载适配器
        spinner.setAdapter(adapter);
//5.设置监听器
        spinner.setOnItemSelectedListener(this);
    }

    @Override//监听事件
    public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
        //String name=(String) adapter.getItem(i);
        String name=(String)list.get(i);
       textview.setText("你选择的城市是"+name);
    }

    @Override
    public void onNothingSelected(AdapterView<?> adapterView) {

    }
}