Android官方下拉选择控件Spinner

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.yechaoa.spinnerdemo.MainActivity">
    <Spinner
        android:id="@+id/spinner1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:entries="@array/letter" />  指定数据源
    <Spinner
        android:id="@+id/spinner2"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1" />
    <Spinner
        android:id="@+id/spinner3"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1" />
</LinearLayout>

package com.yechaoa.spinnerdemo;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
import android.widget.Spinner;
import android.widget.TextView;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity implements AdapterView.OnItemSelectedListener{
    private Spinner spinner1;
    private Spinner spinner2;
    private Spinner spinner3;
    private String[] list1;
    private ArrayList<String> list2;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
        initData();
        initListener();
    }
    /**
     * 初始化控件
     */
    private void initView() {
        spinner1 = (Spinner) findViewById(R.id.spinner1);
        spinner2 = (Spinner) findViewById(R.id.spinner2);
        spinner3 = (Spinner) findViewById(R.id.spinner3);
    }
    /**
     * 初始化数据
     */
    private void initData() {
        list1 = new String[]{"1","2","3"};
        ArrayAdapter<String> adapter=new ArrayAdapter<>(this,android.R.layout.simple_spinner_item, list1);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinner2.setAdapter(adapter);
        list2 = new ArrayList<>();
        list2.add("Android");
        list2.add("IOS");
        list2.add("H5");
        spinner3.setAdapter(new MyAdapter());
    }
    /**
     * 初始化监听器
     */
    private void initListener() {
        spinner1.setOnItemSelectedListener(this);
        spinner2.setOnItemSelectedListener(this);
        spinner3.setOnItemSelectedListener(this);
    }
    /**
     *
     * @param parent parent是你当前所操作的Spinner
     */
    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
        switch (parent.getId()){
            case R.id.spinner1:
                String[] letter = getResources().getStringArray(R.array.letter);
                Log.i("spinner1点击------",letter[position]);
                break;
            case R.id.spinner2:
                Log.i("spinner2点击------",list1[position]);
                break;
            case R.id.spinner3:
                Log.i("spinner3点击------",list2.get(position));
                break;
        }
    }
    /**
     * 没有数据的时候执行
     */
    @Override
    public void onNothingSelected(AdapterView<?> parent) {
    }
    /**
     * 自定义的Adapter
     */
    private class MyAdapter extends BaseAdapter {
        @Override
        public int getCount() {
            return list2.size();
        }
        @Override
        public Object getItem(int i) {
            return null;
        }
        @Override
        public long getItemId(int i) {
            return 0;
        }
        @Override
        public View getView(int position, View convertView, ViewGroup viewGroup) {
            ViewHolder holder ;
            if(convertView==null){
                convertView = LayoutInflater.from(MainActivity.this).inflate(R.layout.item_text, viewGroup, false);
                holder = new ViewHolder();
                holder.itemText= (TextView) convertView.findViewById(R.id.item_text);
                convertView.setTag(holder);
            }else{
                holder = (ViewHolder) convertView.getTag();
            }
            holder.itemText.setText(list2.get(position));
            return convertView;
        }
    }
    class ViewHolder {
        TextView itemText;
    }
}