Android基础TOP4_2：弹窗式选择列表

Activity：

<LinearLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.example.top4_4.MainActivity" >
<TextView
        android:layout_width="fill_parent"
        android:gravity="center_vertical"
        android:layout_height="30dp"
        android:paddingLeft="5dp"
        android:background="#FFA500"
        android:text="Spinner" />
<Spinner 
    android:id="@+id/sp"
    android:layout_width="fill_parent"
    android:layout_height="50dp"
    android:layout_marginTop="20dp"/>
<TextView
        android:id="@+id/tv"
        android:layout_width="fill_parent"
        android:gravity="center_vertical"
        android:layout_height="30dp"
        android:paddingLeft="5dp"
        android:text=""
         />
</LinearLayout>

JAVApublic class MainActivity extends Activity private Spinner sp;

private TextView tv;
private ArrayAdapter aa;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //定义数据源
        String []balls=new String[]{"","足球","篮球","棒球"};
        sp=(Spinner) findViewById(R.id.sp);
        tv=(TextView) findViewById(R.id.tv);
        //找到数据源
        aa=new ArrayAdapter<String>
        (this,android.R.layout.simple_spinner_item,balls);
        aa.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        //给Spinner赋值数据
        sp.setAdapter(aa);
    //当点击时弹出选择列表
    sp.setOnItemSelectedListener(new OnItemSelectedListener() {

        @Override
        public void onItemSelected(AdapterView<?> parent, View view,
                int position, long id) {
            // TODO Auto-generated method stub

            //给TextView选中的数据
            tv.setText(aa.getItem(position).toString());
        }

        @Override
        public void onNothingSelected(AdapterView<?> parent) {
            // TODO Auto-generated method stub
            tv.setText("没有选中任何数据！");
        }
    });