这是在前端显示热门帖子的代码，但问题是数据没有从后端保存。就像我只想在前端显示3个流行帖子，所以我选择了选项3，但它不保存。但是，当我传递的静态值$popularpostcount 那么这个代码就起作用了echo $this->popularPosts($popularpostcount); 因此，我认为问题只在于保存选定的选项。

我是插件开发新手，所以请让我知道在开发过程中我犯了什么错误。

<?php
/*
Plugin Name: Popular Post Widget
Plugin URI: http://demo.test.com
Author: Swapnesh Kumar Sinha
Description: This is a plugin to show popular posts in sidebar as a widget.
Version: 1.0
Author URI: http://swapneshsinha.wordpress.com
*/



class PopularPostWidget extends WP_Widget {

public function __construct() {
    //Widget actual processes
    $widget_options = array( \'Description\' => \'Show Popular Posts\' );
    parent::__construct( \'PopularPostWidget\', \'Popular Post Widget\', $widget_options); 
}

public function form( $instance ) {
    //outputs the options form on admin
$instance = wp_parse_args( (array) $instance, array( \'popularpostcount\' => \'\' ) );
$popularpostcount = $instance[\'popularpostcount\'];  
echo $popularpostcount;
echo "Number of post to show "; 
echo "<select name=\'popularpostcount\' id=\'popularpostcount\'>";
    for( $i =1; $i<=5; $i++ )
    {
        if ( $i == $instance[\'popularpostcount\'] )
        echo "<option value=\'".$i."\' selected>".$i."</option>";
        else
        echo "<option value=\'".$i."\'>".$i."</option>";
    } 
echo "</select>";
}

public function update( $new_instance, $old_instance ) {
    //processes widget options to be saved
    $instance = $old_instance;
    $instance[\'popularpostcount\'] = $new_instance[\'popularpostcount\'];
    return $instance;
}

public function widget( $args ,  $instance ) {
    //outputs the content of widget
    extract($args);
    $popularpostcount = apply_filters(\'widget_title\', $instance[\'popularpostcount\']);
    echo  "<h2>Most Popular Posts</h2>";
    echo  "<ul>";
    echo $this->popularPosts($popularpostcount);
    echo  "</ul>";
}


public function popularPosts($num)
{
     global $wpdb;

    $posts = $wpdb->get_results("SELECT comment_count, ID, post_title FROM $wpdb->posts ORDER BY comment_count DESC LIMIT 0 , $num");

    foreach ($posts as $post) {
        setup_postdata($post);
        $id = $post->ID;
        $title = $post->post_title;
        $count = $post->comment_count;

        if ($count != 0) {
            $popular .= \'<li>\';
            $popular .= \'<a href="\' . get_permalink($id) . \'" title="">\' . $title.\'</a> \'." - ".$count;
            $popular .= \'</li>\';
        }
    }
    return $popular;
}


}

add_action( \'widgets_init\' , create_function(\'\', \'register_widget( "popularpostwidget" );\' ) );