如何下拉到meta box并在db wp中将数据保存在meta data中？

// 添加元框
function custom_meta_box() {
    add_meta_box('custom-meta-box', '自定义元框', 'render_meta_box', 'post', 'normal', 'high');
}
add_action('add_meta_boxes', 'custom_meta_box');

// 渲染元框表单字段
function render_meta_box($post) {
    $selected_value = get_post_meta($post->ID, 'custom-meta-field', true);
    ?>
    <label for="custom-meta-field">选择一个选项：</label>
    <select name="custom-meta-field" id="custom-meta-field">
        <option value="option1" <?php selected($selected_value, 'option1'); ?>>选项1</option>
        <option value="option2" <?php selected($selected_value, 'option2'); ?>>选项2</option>
        <option value="option3" <?php selected($selected_value, 'option3'); ?>>选项3</option>
    </select>
    <?php
}

// 保存元数据
function save_custom_meta_data($post_id) {
    if (array_key_exists('custom-meta-field', $_POST)) {
        update_post_meta($post_id, 'custom-meta-field', $_POST['custom-meta-field']);
    }
}
add_action('save_post', 'save_custom_meta_data');