Detailed explanation of steps to dynamically delete XML data in PHP

<?php
  class Message_XML extends DomDocument{//定义类Message_XML并继承DomDocument类
   private $Root;
   public function construct(){//构造函数
    parent:: construct();
    if(!file_exists("message.xml")){//判断文件是否存在
     $xmlstr="<?xml version=&#39;1.0&#39; encoding=&#39;GB2312&#39;?><message></message>";
     $this->loadXML($xmlstr);
     $this->save("message.xml");//生成XML文档
    }else{
     $this->load("message.xml");//如果存在则载入XML文档
    }
   }
   public function add_message($user,$address){//创建方法
    $Root=$this->documentElement;//定义根节点
    $admin_id=date("Ynjhis");
    $Node_admin_id=$this->createElement("admin_id");//创建节点admin_id
    $text=$this->createTextNode(iconv("GB2312","UTF-8",$admin_id));//创建一个文本节点
    $Node_admin_id->appendChild($text);//将文本节点添加到admin_id节点中
    $Node_user=$this->createElement("user");//创建节点user
    $text=$this->createTextNode(iconv("GB2312","UTF-8",$user));//创建一个文本节点
    $Node_user->appendChild($text);//将文本节点添加到user节点中
    $Node_address=$this->createElement("address");//创建节点address
    $text=$this->createTextNode(iconv("GB2312","UTF-8",$address));//创建一个文本节点
    $Node_address->appendChild($text);//将文本节点添加到address节点中
    $Node_Record=$this->createElement("record");//创建节点record
    $Node_Record->appendChild($Node_admin_id);//将admin_id节点添加到record节点中
    $Node_Record->appendChild($Node_user);//将user节点添加到record节点中
    $Node_Record->appendChild($Node_address);//将address节点添加到record节点中
    $Root->appendChild($Node_Record);//将record节点添加到根节点中
    $this->save("message.xml");//生成XML文档
    echo "<script>alert(&#39;添加成功&#39;);location.href=&#39;".$_SERVER[&#39;PHP_SELF&#39;]."&#39;</script>";
   }
   public function delete_message($admin_id){//定义删除函数
    $Root=$this->documentElement;//定义根节点
    $xpath=new DOMXPath($this);//定义DOMXPath
    $Node_Record=$xpath->query("//record[admin_id=&#39;$admin_id&#39;]");//执行查询语句
    $Root->removeChild($Node_Record->item(0));//删除节点
    $this->save("message.xml");//生成XML文档
    echo "<script>alert(&#39;删除成功&#39;);location.href=&#39;".$_SERVER[&#39;PHP_SELF&#39;]."&#39;</script>";
   }
   public function show_message(){//定义输出XML文件中的内容函数
    $Root=$this->documentElement;//定义根节点
    $xpath=new DOMXPath($this);//定义DOMXPath
    $Node_Record=$this->getElementsByTagName("record");//获取节点record的标签
    $Node_Record_length=$Node_Record->length;//获取标签的数量
    print"<table width=&#39;506&#39; bgcolor=&#39;#FFFFCC&#39;><tr>";
    print"<td width=&#39;106&#39; height=&#39;22&#39; align=&#39;center&#39;>";
    print"<b>用户名</b>";
    print"</td><td width=&#39;300&#39; align=&#39;center&#39;>";
    print"<b>留言信息</b></td></tr>";
    for($i=0;$i<$Node_Record->length;$i++){//应用for循环输出查询结果
     $k=0;
     foreach($Node_Record->item($i)->childNodes as $articles){  //通过foreach语句读取返回对象中的数据
      $field[$k]=iconv("UTF-8","GB2312",$articles->textContent);//实现编码格式的转换
      $k++;
     }
     print"<table width=&#39;506&#39; bgcolor=&#39;#FFFFCC&#39;><tr>";
     print"<td width=&#39;106&#39; height=&#39;22&#39; align=&#39;center&#39;>";
     print"$field[1]";
     print"</td><td width=&#39;300&#39; align=&#39;center&#39;>";
     print"$field[2]";
     print"</td><td width=&#39;100&#39; align=&#39;center&#39;>";
     print"<a href=&#39;?Action=delete_message&admin_id=$field[0]&#39;>删除</a></td>";
     print"</tr></table>";
    }
   }
   public function post_message(){
    print"<table width=&#39;506&#39; bgcolor=&#39;#FFFFCC&#39;><form method=&#39;post&#39; action=&#39;?Action=add_message&#39;>";
    print"<tr><td width=&#39;106&#39; height=&#39;22&#39;>    用户名：</td><td><input type=&#39;text&#39; name=&#39;user&#39; size=50></td></tr>";
    print"<tr><td width=&#39;106&#39; height=&#39;22&#39;>    留言信息：</td><td width=&#39;400&#39;><textarea name=&#39;address&#39; cols=&#39;48&#39; rows=&#39;5&#39; id=&#39;address&#39;></textarea></td></tr>";
    print"<tr><td width=&#39;106&#39; height=&#39;30&#39;>  <input type=&#39;submit&#39; value=&#39;添加数据&#39;></td><td align=&#39;right&#39;><a href=&#39;?Action=show_message&#39;>查看数据</a>    </td></tr></form></table>";
   }
  }
?>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>删除XML数据</title>
<style type="text/css">
<!--
body,td,th {
  font-size: 12px;
}
-->
</style></head>
<body>
<table width="506" height="50" border="0" cellpadding="0" cellspacing="0" bgcolor="#33BE6B">
 <tr>
  <td width="506" height="50" valign="bottom" background="title.gif">
   <table width="506">
    <tr>
     <td height="24" align="right" scope="col">  <a href="?Action=post_message" rel="external nofollow" >添加数据</a>   </td></tr></table></td></tr>
     <?php
      $HawkXML=new Message_XML;//实例化Message_XML类
      $Action="";//初始化为空值
      if(isset($_GET[&#39;Action&#39;])) $Action=$_GET[&#39;Action&#39;];
      switch($Action){
       case "show_message":
       $HawkXML->show_message();//当参数值为show_message时执行show_message()函数
       break;
       case "post_message":
       $HawkXML->post_message();//当参数值为post_message时执行post_message()函数
       break;
       case "add_message":
       $HawkXML->add_message($_POST[&#39;user&#39;],$_POST[&#39;address&#39;]);//当参数值为add_message时执行add_message()函数
       break;
       case "delete_message":
       $HawkXML->delete_message($_GET[&#39;admin_id&#39;]);//当参数值为delete_message时执行delete_message()函数
       break;
      }
     ?>
</table>
</body>
</html>