php - 未在扩展的 PHP DOMElement 上调用构造函数

Question

在 PHP 中扩展 DOMElement 时，不会调用子类的构造函数。就预期行为而言，文档中没有任何内容向我发出警告，但也许我遗漏了一些东西。这是一个简单的测试用例....

 class SillyTestClass extends DOMElement{
    public $foo=null;
    public function __construct($name,$value=null,$namespace=null){
        echo "calling custom construct....";
        $this->foo="bar";
        parent::__construct($name,$value,$namespace);
    }
    public function sayHello(){
        echo "Why, hello there!";
    }
}

$doc=new DOMDocument();
$doc->registerNodeClass('DOMElement','SillyTestClass');
$doc->loadHTML("<div><h1>Sample</h1></div>");
//THIS WORKS! CUSTOM CLASS BEING USED
$doc->documentElement->firstChild->sayHello();

//THIS IS STILL NULL:( Never set by construct, no message saying construct was called either  
echo $doc->documentElement->firstChild->foo; 

当然如果我自己实例化它就好了...

$elm=new SillyTestClass("foo","Hi there");
//WORKS! Outputs "bar";
echo $elm->foo;

为什么当我用 DOMDocument 注册节点类时，它不调用 __construct，即使它以其他方式为我提供了正确的继承？

更新 对于真正好奇的人或了解 C 的人

============================================ ===========================调查....

这是取自 PHP src on github 的 DOM 扩展源

如果你要创建一个元素，这是发生的事件链::

document.c :: dom_document_create_element
    |  //uses libxml to generate a new DOMNode
    | node = xmlNewDocNode(docp, NULL, (xmlChar *) name, (xmlChar *) value);

    // that node is then sent to 
  php_dom.c :: php_dom_create_object
   |
   |  //the node type is used to figure out what extension class to use
   |     switch (obj->type) {...
   |    
   |     //that class is used to instance an object
   |     if (domobj && domobj->document) {
   |          ce = dom_get_doc_classmap(domobj->document, ce);
   |     }
        object_init_ex(return_value, ce);

看起来您并没有从扩展 DOMNode 获得真正的继承，或者如果 DOMDocument 实例化它们，它是内置在扩展类(DOMElement、DOMText)中的。在这种情况下，首先创建 libxml 节点，然后添加我们的类属性。

这看起来很不幸而且不可能绕过，因为即使您将 importNode 导入到文档中，它也会实例化一个新节点。示例

class extendsDE extends DOMElement{
   public $constructWasCalled=false;
    public function __construct($name){
       parent::__construct($name);
       $this->constructWasCalled=true;
   }
}

 class extendsDD extends DOMDocument{

    public function __construct(){
        parent::__construct();
        $this->registerNodeClass("DOMElement","extendsDE");
    }
    //@override
    public function createElement($name){
        $elm=new extendsDE($name);
        echo "Element construct called when we create=";
        echo $elm->constructWasCalled?"true":"false";
        return $this->importNode($elm);
   }
}

$doc=new extendsDD();
$node=$doc->createElement("div");
echo "<br/>";
echo "But then when we import into document, a new element is created  and construct called= ";
echo $node->constructWasCalled?"true":"false"; 

现在的争论 - 这是开发人员的意图并且文档具有误导性，还是它是一个错误并且应该发生真正的继承？

Answer 1

到目前为止，我已经在某些情况下找到了解决此问题的方法。 DOMNodes 保存在内存中，所以只要你能将它一次性放入文档中(调用你的构造函数)，那么无论你用它做什么或之后你如何访问它都可以......

这是一个示例，我们可以在其中调用构造并且仍然可以处理文档

class extendsDE extends DOMElement{
    public $constructWasCalled=false;
    public function __construct($name){
         parent::__construct($name);
          $this->constructWasCalled=true;
   }
  }

   $doc=new DOMDocument();
   $doc->registerNodeClass("DOMElement","extendsDE");
   $doc->loadHTML("<div></div>");

   //append a node we create manually rather than through createElement
   $node=$doc->getElementsByTagName('div')->item(0)->appendChild(new extendsDE("p"));
    $node->nodeValue="Was my construct called?";
     echo "<br/>";
    echo "A new element was appended and construct called= ";
    echo $node->constructWasCalled?"true":"false";
    echo "<br/>";
    echo "Okay but what happens if I retrieve that node some other way..";
    echo "<br/>";
    echo "what if I get that element through selectors. Custom property still set from constructor=";
   echo $doc->getElementsByTagName('p')->item(0)->constructWasCalled?"true":"false";
  echo "<br/>";
  echo "what if I get that element through relationships. Custom property still set from constructor=";
  echo $doc->getElementsByTagName('div')->item(0)->childNodes->item(0)->constructWasCalled?"true":"false";

要点:

这只有在您创建所有元素时才有效。如果您使用 $document->loadHTML($html) 加载 HTML 标记，您的扩展构造函数将不会被调用。到目前为止，我只能想到解决这个问题的破解方法，比如加载标记，然后将每个节点循环到实例副本并插入它们。绝对有可能，但速度很慢......