您需要保存所选内容，然后将所选值调用到widget() 方法

下面是我的意思示例，它在前端显示所选类别名称和描述。您可以使用此小部件作为自己小部件的基础。请注意，此小部件至少需要PHP 5.4

/**
 * Select_Category widget class
 *
 * Display a selected category
 *
 * @since 1.0.0
*/
class Select_Category extends WP_Widget 
{

    public function __construct() 
    {
        parent::__construct(
            \'widget_selected_category\', 
            _x( \'Selected Category Widget\', \'Selected Category Widget\' ), 
            [ \'description\' => __( \'Display a selected category.\' ) ] 
        );
        $this->alt_option_name = \'widget_selected_category\';

        add_action( \'save_post\', [$this, \'flush_widget_cache\'] );
        add_action( \'deleted_post\', [$this, \'flush_widget_cache\'] );
        add_action( \'switch_theme\', [$this, \'flush_widget_cache\'] );
    }

    public function widget( $args, $instance ) 
    {
        $cache = [];
        if ( ! $this->is_preview() ) {
            $cache = wp_cache_get( \'widget_selected_cat\', \'widget\' );
        }

        if ( ! is_array( $cache ) ) {
            $cache = [];
        }

        if ( ! isset( $args[\'widget_id\'] ) ) {
            $args[\'widget_id\'] = $this->id;
        }

        if ( isset( $cache[ $args[\'widget_id\'] ] ) ) {
            echo $cache[ $args[\'widget_id\'] ];
            return;
        }

        ob_start();

        $title          = ( ! empty( $instance[\'title\'] ) ) ? $instance[\'title\'] : __( \'Category Posts\' );
        /** This filter is documented in wp-includes/default-widgets.php */
        $title          = apply_filters( \'widget_title\', $title, $instance, $this->id_base );
        if ( ! $number ) {
            $number = 5;
        }
        $cat_id       = $instance[\'cat_id\'];


        echo $args[\'before_widget\'];
        if ( $title ) {
            echo $args[\'before_title\'] . $title . $args[\'after_title\'];
        }   

        $select_cat_object = get_category( $cat_id );
        echo \'Your selected category is \' . $select_cat_object->name;
        echo "\\n\\t";
        echo $select_cat_object->description;

        echo $args[\'after_widget\']; 

        if ( ! $this->is_preview() ) {
            $cache[ $args[\'widget_id\'] ] = ob_get_flush();
            wp_cache_set( \'widget_selected_cat\', $cache, \'widget\' );
        } else {
            ob_end_flush();
        }
    }

    public function update( $new_instance, $old_instance ) 
    {
        $instance                   = $old_instance;
        $instance[\'title\']          = strip_tags( $new_instance[\'title\'] );
        $instance[\'cat_id\']         = (int) $new_instance[\'cat_id\'];

        $this->flush_widget_cache();

        $alloptions = wp_cache_get( \'alloptions\', \'options\' );
        if ( isset($alloptions[\'widget_selected_category\']) )
            delete_option(\'widget_selected_category\');

        return $instance;
    }

    public function flush_widget_cache() 
    {
        wp_cache_delete(\'widget_selected_cat\', \'widget\');
    }

    public function form( $instance ) 
    {

        $title  = isset( $instance[\'title\'] ) ? esc_attr( $instance[\'title\'] ) : \'\';
        $cat_id = isset( $instance[\'cat_id\'] ) ? absint( $instance[\'cat_id\'] ) : 1;
        ?>

        <p>
            <label for="<?php echo $this->get_field_id( \'title\' ); ?>"><?php _e( \'Title:\' ); ?></label>
            <input class="widefat" id="<?php echo $this->get_field_id( \'title\' ); ?>" name="<?php echo $this->get_field_name( \'title\' ); ?>" type="text" value="<?php echo $title; ?>" />
        </p>

        <p>
            <label for="<?php echo $this->get_field_id(\'cat_id\'); ?>"><?php _e( \'Category Name:\' )?></label>
            <select id="<?php echo $this->get_field_id(\'cat_id\'); ?>" name="<?php echo $this->get_field_name(\'cat_id\'); ?>">
                <?php 
                $this->categories = get_categories();
                foreach ( $this->categories as $cat ) {
                    $selected = ( $cat->term_id == esc_attr( $cat_id ) ) ? \' selected = "selected" \' : \'\';
                    $option = \'<option \'.$selected .\'value="\' . $cat->term_id;
                    $option = $option .\'">\';
                    $option = $option .$cat->name;
                    $option = $option .\'</option>\';
                    echo $option;
                }
                ?>
            </select>
        </p>

    <?php
    }

}

add_action( \'widgets_init\', function () 
{
    register_widget( \'Select_Category\' );
});