既然您正在学习 OOP，那么是时候了解一下Abstract Classes (PHP Manual)！
抽象类是一种定义了一系列通用函数的骨架类。一个抽象类永远不能被实例化（即，你不能调用new AbstractClass），但可以被其他类extended。这允许我们定义一些通用和可重复的东西，比如 HTML 元素，然后随着时间的推移将其扩展到特定的 HTML 元素。这是该概念的示例实现。
警告：我并不是说 这个 实现是个好主意；仅用于学习目的！
首先，一些抽象类来定义这些东西应该如何工作。
abstract class HTMLWriter
{
protected $html = '';
protected $tagName = null;
protected $selfClosing = false;
protected $elements = array();
protected $attributes = array();
protected $closed = false;
abstract public function __construct();
public function addElement(HTMLWriter $element)
{
if ($this->closed || $this->selfClosing) {
return;
}
$element->close(); // automatic!
$this->elements[] = $element->write();
}
public function addElements() {
foreach (func_get_args() as $arg) {
if ($arg instanceof HTMLWriter) {
$this->addElement($arg);
}
}
}
public function addAttribute($name, $value)
{
return $this->attributes[$name] = $value;
}
public function write()
{
if (!$this->closed) {
$this->close();
}
return $this->html;
}
public function close()
{
$this->closed = true;
$this->html = '<' . $this->tagName;
foreach ($this->attributes AS $attr => $val) {
$this->html .= ' ' . $attr . '="' . $val . '"';
}
if ($this->selfClosing) {
$this->html .= '/>';
return;
}
$this->html .= '>';
foreach($this->elements as $elem) {
$this->html .= $elem;
}
$this->html .= '</' . $this->tagName . '>';
}
}
abstract class HTMLWriterWithTextNodes extends HTMLWriter
{
//abstract public function __construct();
public function addText($text)
{
$this->elements[] = htmlentities($text);
}
public function addTextRaw($text)
{
$this->elements[] = $text;
}
}
然后是这些类的具体实现：
注意：具体类是任何非抽象类，尽管该术语在应用于不是抽象类扩展的类时失去了意义。
class Form extends HTMLWriter
{
public function __construct($action, $method, $can_upload = false)
{
$this->tagName = 'form';
$this->addAttribute('action', $action);
$this->addAttribute('method', $method);
if ($can_upload) {
$this->addAttribte('enctype','multipart/form-data');
}
}
}
class Input extends HTMLWriter
{
public function __construct($type, $name, $id = null)
{
$this->tagName = 'input';
$this->selfClosing = true;
$this->addAttribute('type', $type);
$this->addAttribute('name', $name);
if (!is_null($id)) {
$this->addAttribute('id', $id);
}
}
// overrides
public function addElement()
{
return false;
}
}
class Label extends HTMLWriterWithTextNodes
{
public function __construct($labelText = null, $for = null)
{
$this->tagName = 'label';
if (!is_null($labelText)) {
$this->elements[] = $labelText;
}
if (!is_null($for)) {
$this->addAttribute('for', $for);
}
}
}
class GenericElement extends HTMLWriterWithTextNodes
{
public function __construct($tagName, $selfClosing = false)
{
if (empty($tagName)) {
$this->closed = true;
$this->html = '';
return;
}
$this->tagName = $tagName;
$this->selfClosing = (bool)$selfClosing;
}
}
最后，让我们实例化并使用我们的新类
$form = new Form('/class_lib.php','get');
$username = new Input('text','username','username');
$password = new Input('password','password','password');
$submit = new Input('submit','login');
$submit->addAttribute('value','login');
$ulabel = new Label('Username: ', 'username');
$plabel = new Label('Password: ','password');
$br = new GenericElement('br',true);
$form->addElements(
$ulabel, $username, $br,
$plabel, $password, $br,
$submit
);
echo $form->write();
输出：
<form action="/class_lib.php" method="get"><label for="username">Username: </label><input type="text" name="username" id="username"/><br/><label for="password">Password: </label><input type="password" name="password" id="password"/><br/><input type="submit" name="login" value="login"/></form>
抽象类万岁！