3.7下拉控件

 1.Spinner(下拉列表)是一个每次只能选择所有项中一项的控件，相当于Html中的下拉列表框。它的继承关系如下：
java.lang.Object 
 ↳ android.view.View 
   ↳ android.view.ViewGroup 
     ↳ android.widget.AdapterView<T extends android.widget.Adapter> 
        ↳ android.widget.AbsSpinner 
           ↳ android.widget.Spinner

2.创建使用Spinner的步骤如下：

①需要在布局中定时Spinner组件，然后向Spinner添加需要选择的数据

②设置事件监听器setOnItemSelectedListener( )并实现onItemSelected( )

3.Spinner添加数据的两种方法：

①在Java代码中载入列表数据
  

界面:

值:

<resources>
    <string name="app_name">Spinnerliang</string>
    <string-array name="cityarr">
        <item>hangzhou</item>
        <item>ningbo</item>
        <item>wenzhou</item>
    </string-array>
</resources>

布局:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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: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.liang.spinnerliang.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="City:"
        android:id="@+id/textView"
        android:layout_alignParentTop="true"
        android:layout_alignParentStart="true" />

    <Spinner
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/spinner"
        android:layout_alignParentTop="true"
        android:layout_toEndOf="@+id/textView" />
</RelativeLayout>

程序:

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.Toast;

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

public class MainActivity extends AppCompatActivity {
    private Spinner spinner;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        spinner= (Spinner) this.findViewById(R.id.spinner);

        //方法一 实例一个ArrayAdapter
        /*  ArrayAdapter<String> stradapter=new ArrayAdapter(MainActivity.this,android.R.layout.simple_spinner_dropdown_item,getStringList());
        spinner.setAdapter(stradapter);*/

        //方法二 从xml取数组
        ArrayAdapter<CharSequence>  csadapter=ArrayAdapter.createFromResource(MainActivity.this, R.array.cityarr,android.R.layout.simple_spinner_item);
        csadapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinner.setAdapter(csadapter);

        //监听事件
        spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                String s=parent.getItemAtPosition(position).toString();
                Toast.makeText(MainActivity.this,"selected:"+s,Toast.LENGTH_SHORT).show();
            }

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

            }
        });
    }

    private List<String> getStringList() {
        List<String> list=new ArrayList<String>();
        list.add("beijing");
        list.add("shanghai");
        list.add("guangzhou");
        return list;
    }
}