安卓:当点击视图下拉菜单时，会显示一个textView

<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"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/dropdownButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="下拉菜单"
        android:layout_centerInParent="true"/>

    <TextView
        android:id="@+id/resultTextView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/dropdownButton"
        android:layout_centerInParent="true"
        android:text="选择的选项将会显示在这里"
        android:visibility="invisible"/> // 初始化时设置为不可见
</RelativeLayout>

import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity implements AdapterView.OnItemSelectedListener {

    private Button dropdownButton;
    private TextView resultTextView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        dropdownButton = findViewById(R.id.dropdownButton);
        resultTextView = findViewById(R.id.resultTextView);

        dropdownButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                resultTextView.setVisibility(View.VISIBLE); // 设置TextView可见
            }
        });
    }
}

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.myapplication">

    <application
        ...
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        ...
    </application>
</manifest>