Spinner提供一種方法，可以讓使用者從數據集合中快速選擇一個值

Spinner的UI設計

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

    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/what"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="今晚你想吃什麼?"
        android:textSize="20sp" />
    <Spinner
        android:id="@+id/spinner"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
    />
</LinearLayout>

Spinner的程式設計

回到MainActivity

package com.example.spinner;
import androidx.appcompat.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.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    //宣告物件
    private Spinner spinner;
    private String[] dinner ={"鐵板燒","鍋燒意麵","拉麵","炒飯","蛋包飯","漢堡薯條","牛排"};// 建立資料來源

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();
        Useadapter();
        setSpinner();
    }
    private void setSpinner() {
        spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                String food =parent.getItemAtPosition(position).toString();
                Toast.makeText(MainActivity.this, "我想吃:" + food, Toast.LENGTH_SHORT).show();
            }
            @Override
            public void onNothingSelected(AdapterView<?> parent) {
            }
        });
    }
    private void Useadapter() {
        ArrayAdapter<String> dinnerList = new ArrayAdapter<>(MainActivity.this,
        android.R.layout.simple_spinner_dropdown_item,dinner);// 建立Adapter並且連結資料來源
        spinner.setAdapter(dinnerList);//連結 Adapter到控制元件
    }
    private void init() {
    spinner= findViewById(R.id.spinner);
    }
}

onItemSelected:當使用者選中Spinner選項時所執行的方法，那onNothingSelected則是當使用者沒選中Spinner選項時所執行的方法