如何在android中实现多级菜单(下拉菜单)

// MainActivity.java

public class MainActivity extends AppCompatActivity {
    private Spinner spinner1;
    private Spinner spinner2;

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

        spinner1 = findViewById(R.id.spinner1);
        spinner2 = findViewById(R.id.spinner2);

        ArrayAdapter<CharSequence> adapter1 = ArrayAdapter.createFromResource(this, R.array.menu_items_1, android.R.layout.simple_spinner_item);
        adapter1.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinner1.setAdapter(adapter1);

        spinner1.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                String selectedItem = parent.getItemAtPosition(position).toString();
                if (selectedItem.equals("Menu 1")) {
                    ArrayAdapter<CharSequence> adapter2 = ArrayAdapter.createFromResource(MainActivity.this, R.array.menu_items_2_1, android.R.layout.simple_spinner_item);
                    adapter2.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
                    spinner2.setAdapter(adapter2);
                } else if (selectedItem.equals("Menu 2")) {
                    ArrayAdapter<CharSequence> adapter2 = ArrayAdapter.createFromResource(MainActivity.this, R.array.menu_items_2_2, android.R.layout.simple_spinner_item);
                    adapter2.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
                    spinner2.setAdapter(adapter2);
                }
            }

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

        spinner2.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                String selectedItem = parent.getItemAtPosition(position).toString();
                Toast.makeText(MainActivity.this, selectedItem, Toast.LENGTH_SHORT).show();
            }

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        if (id == R.id.menu_item1) {
            // 处理菜单项1的点击事件
            return true;
        } else if (id == R.id.menu_item2) {
            // 处理菜单项2的点击事件
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

<!-- activity_main.xml -->

<LinearLayout 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:orientation="vertical"
    android:padding="16dp"
    tools:context=".MainActivity">

    <Spinner
        android:id="@+id/spinner1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <Spinner
        android:id="@+id/spinner2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

<!-- main_menu.xml -->

<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/menu_item1"
        android:title="Menu 1" />
    <item
        android:id="@+id/menu_item2"
        android:title="Menu 2" />
</menu>

<!-- strings.xml -->

<resources>
    <string-array name="menu_items_1">
        <item>Menu 1</item>
        <item>Menu 2</item>
    </string-array>

    <string-array name="menu_items_2_1">
        <item>Submenu 1-1</item>
        <item>Submenu 1-2</item>
    </string-array>

    <string-array name="menu_items_2_2">
        <item>Submenu 2-1</item>
        <item>Submenu 2-2</item>
    </string-array>
</resources>