如何让导航图标在点击时打开下拉菜单？(Android)

<androidx.appcompat.widget.Toolbar
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    android:background="@color/colorPrimary"
    android:elevation="4dp"
    android:theme="@style/ThemeOverlay.AppCompat.ActionBar"
    app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);

<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/action_menu"
        android:icon="@drawable/ic_menu"
        android:title="Menu"
        android:orderInCategory="1"
        app:showAsAction="always">
        <menu>
            <item
                android:id="@+id/item1"
                android:title="Item 1" />
            <item
                android:id="@+id/item2"
                android:title="Item 2" />
        </menu>
    </item>
</menu>

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

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

    if (id == R.id.action_menu) {
        // 点击了导航图标，打开下拉菜单
        PopupMenu popupMenu = new PopupMenu(this, findViewById(R.id.action_menu));
        popupMenu.inflate(R.menu.menu_main);
        popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
            @Override
            public boolean onMenuItemClick(MenuItem item) {
                // 处理下拉菜单项的点击事件
                int itemId = item.getItemId();
                if (itemId == R.id.item1) {
                    // 点击了Item 1
                    // TODO: 处理Item 1的逻辑
                    return true;
                } else if (itemId == R.id.item2) {
                    // 点击了Item 2
                    // TODO: 处理Item 2的逻辑
                    return true;
                }
                return false;
            }
        });
        popupMenu.show();
        return true;
    }

    return super.onOptionsItemSelected(item);
}