前兩篇介紹ListView和GridView元件，而這篇再介紹ListView和GridView的好朋友Spinner。Spinner在app常見於填寫資料，由於有選擇的特性能幫助使用者將資料快速填寫完畢。

Spinner

Spinner在spinner選單裡每一格由一個view組成，view裡有元件或物件(字串)。

Spinner-UI程式設計

相信大家看到第十二篇，底下的程式應該易如反掌，那我們飛過去吧!

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

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

GridView-Java程式設計

Spinner使用的偵聽方式是setOnItemSelectedListener選擇選項，因此，特別介紹OnItemSelectedListener()要覆寫的方法。

    private void setAdapter(){
        ArrayAdapter <String> adapter=
        new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,fruit_name);
        adapter.setDropDownViewResource(android.R.layout.simple_list_item_activated_1);
        spinner.setAdapter(adapter);
    }

• adapter.setDropDownViewResource
  提供選單的樣式
• simple_list_item_activated_1
  點選後，選單會改變背景顏色

    private void setListener() {

        spinner.setOnItemSelectedListener(new Spinner.OnItemSelectedListener() {
            @Override
            
           public void onItemSelected
           (AdapterView<?> adapterView, View view, int position, long l) {
                String msg = adapterView.getItemAtPosition(position).toString();
                setToast(msg);
            }
            
            @Override
            public void onNothingSelected(AdapterView<?> adapterView) {

            }
        });

• onItemSelected與onNothingSelected=>白話的意思是選擇選項與沒有選擇選項所要執行的方法

完整程式碼

public class MainActivity extends AppCompatActivity {
    private Spinner spinner;
    private String[] fruit_name=new String[]{"Apple","Banana","Orange","Grape","Strawberry"};

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        findViews();
        setAdapter();
        setListener();
    }
        
    private void setAdapter(){
        ArrayAdapter <String> adapter=
        new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,fruit_name);
        adapter.setDropDownViewResource(android.R.layout.simple_list_item_activated_1);
        spinner.setAdapter(adapter);
    }
    
    private void findViews () {
          spinner=(Spinner)findViewById(R.id.spinner);
     }

     private void setToast (String text){
          Toast.makeText(MainActivity.this, text, Toast.LENGTH_SHORT).show();
     }

    private void setListener() {

        spinner.setOnItemSelectedListener(new Spinner.OnItemSelectedListener() {
            @Override
            
           public void onItemSelected
           (AdapterView<?> adapterView, View view, int position, long l) {
                String msg = adapterView.getItemAtPosition(position).toString();
                setToast(msg);
            }
            
            @Override
            public void onNothingSelected(AdapterView<?> adapterView) {

            }
        });
    }
    }

實作

若文章有誤，歡迎大家提出建議。

Thank you for your time.