实例化类并通过动作

Question

我正在阅读刚与代码融为一体的PHP入门书籍。 我只停留在这个例子上，我不知道发生了什么。 有人可以帮忙解释一下发生了什么吗？

此类似乎已实例化，默认情况是列出记录到数据库中的帖子：

<?php
require_once('../includes/admin.php');

$admin_posts = new Posts;

调用该类时，默认情况下会加载将ID和操作传递到上述php文件的选项，然后它将解析并调用另一个方法。 就我而言，我试图删除帖子，但我不断收到一条错误消息，指出未找到对象。

<?php
session_start();
require_once('database.php');
class Adminpanel{
    public function __construct(){
        $inactive = 600;
        if (isset($_SESSION["kickstart_login"])) {
            $sessionTTL = time() - $_SESSION["timeout"];
            if ($sessionTTL > $inactive) {
                session_unset();
                session_destroy();
                header("Location: http://".$_SERVER['SERVER_NAME']."/login.php?status=inactive");
            }
        }
        $_SESSION["timeout"] = time();
        $login = $_SESSION['kickstart_login'];
        if(empty($login)){
            session_unset();
            session_destroy();
            header('Location: http://'.$_SERVER['SERVER_NAME'].'/login.php?status=loggedout');
        }else{
            $this->ksdb = new Database;
            $this->base = (object) '';
            $this->base->url = 'http://'.$_SERVER['SERVER_NAME'];
        }
    }
}

class Posts extends Adminpanel{

    public function __construct(){
        parent::__construct();
        if(!empty($_GET['action'])){
            switch ($_GET['action']){
                case 'create':
                    $this->addPost();
                    break;
                default:
                    $this->listPosts();
                    break;
                case 'save':
                    $this->savePost();
                    break;
                case 'edit':
                    echo "string";
                    $this->editPosts();
                    break;
                case 'delete':
                    $this->deletePost();
                    break;
            }
        }else{
            $this->listPosts();
        }
    }

    public function listPosts(){
        $posts = $return = array();
        $query = $this->ksdb->db->prepare("SELECT * FROM posts");
        try {
            $query->execute();
            for($i=0; $row = $query->fetch(); $i++){
                $return[$i] = array();
                foreach($row as $key => $rowitem){
                    $return[$i][$key] = $rowitem;
                }
            }
        }catch (PDOException $e) {
            echo $e->getMessage();
        }
        $posts = $return;
        require_once('templates/manageposts.php');
    }

    public function editPosts(){
        echo "string";
    }

    public function addPost(){
        require_once('templates/newpost.php');
    }

    public function savePost(){
        $status= '';
        $array = $format = $return = array();
        if(!empty($_POST['post'])){
            $post = $_POST['post'];
        }
        if(!empty($post['content'])){
            $array['content'] = $post['content'];
            $format[] = ':content'; 
        }
        if(!empty($post['title'])){
            $array['title'] = $post['title'];
            $format[] = ':title'; 
        } 
        $cols = $values = '';
        $i=0;
        foreach($array as $col => $data){
            if($i==0){
                $cols .= $col;
                $values .= $format[$i];
            }else{
                $cols .= ','.$col;
                $values .= ','.$format[$i];
            }
            $i++;
        }
        try {
            $query = $this->ksdb->db->prepare("INSERT INTO posts(".$cols.") VALUES (".$values.")");
            for($c=0;$c<$i;$c++){
                $query->bindParam($format[$c], ${'var'.$c});
            }
            $z=0;
            foreach($array as $col => $data){
                ${'var' . $z} = $data;
                $z++;
            }
            $result = $query->execute();
            $add = $query->rowCount();
        }catch (PDOException $e) {
            echo $e->getMessage();
        }
        $query->closeCursor();
        $this->db = null;
        if(!empty($add) && $add > 0){
            $status = array('success' => 'Your post has been saved successfully.');
            $key = 'success';
        }else{
            $status = array('error' => 'There has been an error saving your post. Please try again later.');
            $key = 'error';
        }
        header("Location: ".$this->base->url."/posts.php?status=".$key);        
    }

    public function deletePost(){
        echo "string";
        // if(!empty($_GET['id']) && is_numeric($_GET['id'])){
        //  $query = "DELETE FROM `posts` WHERE id = ".$_GET['id'];
        //  $result = $this->db->query($query);
        //  $delete = $result->rowCount();
        //  $this->db = null;
        //  if(!empty($delete) && $delete > 0){
        //      header("Location: ".$this->base->url."/posts.php?delete=success");
        //  }else{
        //      header("Location: ".$this->base->url."/posts.php?delete=error");
        //  }
        // }    
    }

}

class Comments extends Adminpanel{

    public function __construct(){
        parent::__construct();
        if(!empty($_GET['action']) && $_GET['action'] == 'delete'){
            $this->deleteComment();
        }else{
            $this->listComments();
        }
    }

    public function listComments(){
        $comments = $return = array();
        $query = $this->ksdb->db->prepare("SELECT * FROM comments");
        try {
            $query->execute();
            for($i=0; $row = $query->fetch(); $i++){
                $return[$i] = array();
                foreach($row as $key => $rowitem){
                    $return[$i][$key] = $rowitem;
                }
            }
        }catch (PDOException $e) {
            echo $e->getMessage();
        }
        $comments = $return;
        require_once('templates/managecomments.php');
    }

    public function deleteComment(){
        if(!empty($_GET['id']) && is_numeric($_GET['id'])){
            $query = "DELETE FROM `comments` WHERE id = ".$_GET['id'];
            $result = $this->db->query($query);
            $delete = $result->rowCount();
            $this->db = null;
            if(!empty($delete) && $delete > 0){
                header("Location: ".$this->base->url."/comments.php?delete=success");
            }else{
                header("Location: ".$this->base->url."/comments.php?delete=error");
            }
        }   
    }

}

$admin = new Adminpanel();