如果你没有示例化一个Comment示例，你就不能访问$this-〉db_handle。
你可以考虑像下面这样做：

static function GetCommentByBookId($id) {
     echo "Entered 'GetCommentByBookId'<br>";
     $query = "SELECT * FROM comment WHERE book_id = ?";
     $paramType = "i";
     $paramValue = array(
        $id
     );
            
     echo "Pre-Ex 'GetCommentByBookId'<br>";
            
     $result = (new DBController())->runQuery($query, $paramType, $paramValue);
            
    echo "Executed successfully 'GetCommentByBookId'<br>";

    return $result;
}

**问题：**但是为什么调用静态函数不起作用？
**答案：**因为当你调用类外的静态方法时，该类的构造不会运行，因此如果你调用依赖于构造类的任何其他属性，你会得到错误。

在你的例子中，当你在静态方法中调用static function GetCommentByBookId($id)时，你现在调用的是$result = $this->db_handle->runQuery($query, $paramType, $paramValue);，因为构造没有运行，因此当你调用静态方法时，this->handle没有示例化这个类，因此你得到了$this->db_handle->runQuery的错误。

示例

我已经重建了你的代码，你解释我的意思。请看一下代码和结果图像。

<?php 
error_reporting(E_ERROR |  E_PARSE);
ini_set('display_errors', '1');

 class Comment {

         function __construct() {
            $this->dbconnection = new DBController();
            echo "<br>construct was invoked and this msg is from construct of the comment class <br>";
            
        }
        
        //static way
         static function GetCommentByBookId($id) {
         $result = new DBController();
         $result = $result->runQuery('query here');

           return $result."here are the comments for Book ID - " . $id;
        }

        //normal way
        function GetCommentByBookId2($id) {
        $result = $this->dbconnection;
         $result = $result->runQuery('query here');

           return $result."here are the comments for Book ID - " . $id;
        }

    }



class DBController{

    function runQuery(){
        return "database connected and query was executed <br>";
    }
}



class Book {
             
        //this function uses normal method in comment class
        function GetBookById($id) {
            $c = new comment;
            $result = $c->GetCommentByBookId2(1);
            // $result = Comment::GetCommentByBookId($id);
            return $result;
        }

         //this function uses static method in comment class. No class instanciated. 
        function GetBookById2($id) {
            
            $result = Comment::GetCommentByBookId($id);
            return $result;
        }

       
    }

//using classes.

echo '<hr> <strong>Without Static Method</strong> <br> Here we called normal public method defined in the comments class. Here constructor is invoked<br><br><br>';

$bookinfo = new Book;
echo $bookinfo->GetBookById(2) ;

echo '<hr> <strong>Static Method</strong> <br> Here we called the static method defined in the comments class. We get the result because we are instanciating the DB class in static method. In static Construct did not run<br><br>';
echo $bookinfo->GetBookById2(3) ;
 ?>

• 结果：* x1c 0d1x

如果您有任何疑问/问题或发现不正确的东西，请评论。