1.创建Spinner控件

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

2.创建下拉框的数据源

List<String> list = new ArrayList<String>();
list.add("香蕉")
list.add("苹果")
list.add("橘子")
list.add("橙子")

3.创建适配器Adapter

ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,android.R.layout.simple_spinner_items,list)

4.为适配器添加样式

adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_items);

5.向控件spinner添加适配器

Spinner sp = (Spinner) findViewById(R.id.spinner);
sp.setAdapter(adapter);

6.实现选择项事件

sp.setOnItemSelectedListener(new OnItemSelectedListener()){
    public void onItemSelected(AdapterView<?> parent,View view, int position, long id){
        TextView tvResult = (TextView) findViewById(R.id.tvResult);
        
        ArrayAdapter<String> adapter = (ArrayAdapter<String>) parent.getAdapter();
        tvResult.setText(adapter.getItem(position));
    }
}

public void onNothingSelected(AdapterView<?> parent){
}
});

7.整体代码

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        List<String> list = new ArrayList<String>();
        list.add("苹果");
        list.add("香蕉");
        list.add("橘子");
        list.add("香蕉");
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, list);
        adapter.setDropDownViewResource(android.R.layout.simple_list_item_single_choice);
        Spinner sp = (Spinner) findViewById(R.id.spinner1);
        sp.setAdapter(adapter);
        sp.setOnItemSelectedListener(new OnItemSelectedListener() {
// parent： 为控件Spinner view：显示文字的TextView position：下拉选项的位置从0开始 
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            TextView tvResult = (TextView) findViewById(R.id.tvResult);
//获取Spinner控件的适配器
            ArrayAdapter<String> adapter = (ArrayAdapter<String>) parent.getAdapter();
            tvResult.setText(adapter.getItem(position));
    }
//没有选中时的处理
        public void onNothingSelected(AdapterView<?> parent) {
        }
        });
    }