扩展DOMDocument和DOMNode：返回对象的问题 [英] Extending DOMDocument and DOMNode: problem with return object

问题描述

我正在尝试扩展DOMDocument类，以便使XPath选择更容易。我写了这段代码：

I'm trying to extend the DOMDocument class so as to make XPath selections easier. I wrote this piece of code:

class myDOMDocument extends DOMDocument {

 function selectNodes($xpath){
   $oxpath = new DOMXPath($this);
    return $oxpath->query($xpath);
  }

  function selectSingleNode($xpath){
   return $this->selectNodes($xpath)->item(0);
  }
}

这些方法分别返回一个DOMNodeList和一个DOMNode对象。
我现在想做的是对DOMNode对象实现类似的方法。但是显然，如果我编写一个扩展DOMNode的类（myDOMNode），我将无法在myDOMDocument返回的节点上使用这两个额外的方法，因为它们是DOMNode（而不是myDOMNode）对象。

These methods return a DOMNodeList and a DOMNode object, respectively. What I'd like to do now is to implement similar methods to the DOMNode objects. But obviously if I write a class (myDOMNode) that extends DOMNode, I won't be able to use these two extra methods on the nodes returned by myDOMDocument because they're DOMNode (and not myDOMNode) objects.

我是一个对象编程的初学者，我尝试了各种想法，但都会导致死胡同。

I'm rather a beginner in object programming, I've tried various ideas but they all lead to a dead-end.

任何提示？非常感谢。

推荐答案

尝试使用封装而不是继承。也就是说，编写一个类可以扩展本机DOMNode类，而不是编写一个DOMNode类的实例，并且只提供你需要的方法。

Try using encapsulation instead of inheritance. That is, instead of writing a class that extends the native DOMNode class, write a class stores an instance of DOMNode inside it, and provides only the methods you need.

允许您编写一个有效将DOMNode转换成MyNode的构造函数：

This allows you to write a constructor that effective turns a DOMNode into a MyNode:

class MyNode {
   function __construct($node) {
      $this->node = $node;
   }

   // (other helpful methods)

}

对于MyDocument类，输出MyNode对象而不是DOMNode对象：

For your class MyDocument, you output MyNode objects rather than DOMNode objects:

class MyDocument {

   // (other helpful methods)

   function selectSingleNode($xpath) {

      return new MyNode($this->selectNodes($xpath)->item(0));
   }
}

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