Spinner有兩種型態，第一種是下拉式(dropdown)、第二種是對話式(dialog)
可以在android:spinnerMode=" "，選擇想要的模式

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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">

    <Spinner
        android:id="@+id/spinner"
        android:layout_width="match_parent"
        android:layout_height="100dp"
        android:spinnerMode="dialog"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0" />
</androidx.constraintlayout.widget.ConstraintLayout>

程式碼:(裡面有詳細註解)

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.Toast;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //綁定元件
        Spinner spinner = findViewById(R.id.spinner);
        //建立選項文字
        final String[] str = {"第0", "第1", "第2", "第3", "第4", "第5"};
        ArrayAdapter<String> strList = new ArrayAdapter(MainActivity.this,  //對應的Context
                android.R.layout.simple_spinner_dropdown_item,  //未展開時樣式
                str);   //上方剛設定的String[]資料
        spinner.setAdapter(strList);    //指定給要操作spinner
        
        //展開時樣式,可不設置
        strList.setDropDownViewResource(android.R.layout.simple_list_item_single_choice); 
        
        spinner.setSelection(3);    //顯示一開始要出現的選項，若不設置預設為0

        //spinner點擊監聽
        spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> adapterView, View view, int i, long l) {
                // 選項有選取時的動作
                Toast.makeText(MainActivity.this, "您選擇了:" + spinner.getSelectedItem().toString(), Toast.LENGTH_SHORT).show();
                //getSelectedItem()是所選擇的選項內容
            }

            @Override
            public void onNothingSelected(AdapterView<?> adapterView) {
                // 沒有選取時的動作
            }
        });
    }
}

執行畫面:

選項內容: