Android学习-使用Spinner实现下拉列表

package com.example.angel.listviewpro;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public class MainAcitivity extends AppCompatActivity implements AdapterView.OnItemSelectedListener {

private TextView textView;
private Spinner spinner;
private List<String> list;
private ArrayAdapter<String>adapter;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_layout);

textView = (TextView) findViewById(R.id.textView);
spinner = (Spinner)findViewById(R.id.spinner);
textView.setText("您选择的城市是北京");
//1.数据源
list = new ArrayList<>();
list.add("北京");
list.add("上海");
list.add("广州");
list.add("深圳");
//2.新建ArrayAdapter(只是文字，所以选择这个适配器)
adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,list);
//3.设置下拉列表样式
//setDropDownViewResource(int resource)
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
//4.加载适配器
spinner.setAdapter(adapter);
//5.spinner设置监听器
spinner.setOnItemSelectedListener(this);
}
public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
String cityName = adapter.getItem(i);
//list.get(i);与上一行相同
textView.setText("您选择的是"+cityName);
}

public void onNothingSelected(AdapterView<?> adapterView) {

}
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">

<TextView
android:id="@+id/textView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textSize="25sp"
android:textColor="#ff0000"/>
<Spinner
android:id="@+id/spinner"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>

</LinearLayout>