具体分析如下：

用户在关注与取消关注公众号时,微信会把这个事件推送到开发者填写的URL,方便开发者给用户下发欢迎消息或者做帐号的解绑.

下面是一个微信公众平台关注和取消关注的实例,代码如下:

复制代码 代码如下:

define("TOKEN", "w3note");//定义识别码
$wechatObj = new wechatCallbackapiTest();//实例化wechatCallbackapiTest类
 
if(!isset($_GET["echostr"])){
     $wechatObj->responseMsg();
}else{
 $wechatObj->valid();
}
class wechatCallbackapiTest
{
 public function valid()
    {
        $echoStr = $_GET["echostr"];
        if($this->checkSignature()){
         echo $echoStr;
         exit;
        }
    }
    public function responseMsg()//执行接收器方法
    {
    $postStr = $GLOBALS["HTTP_RAW_POST_DATA"];
    if (!emptyempty($postStr)){
      $postObj = simplexml_load_string($postStr, 'SimpleXMLElement', LIBXML_NOCDATA);
      $RX_TYPE = trim($postObj->MsgType);
      switch($RX_TYPE){
       case "event":
       $result = $this->receiveEvent($postObj);
       breadk;
      }
      echo $result;
  }else{
   echo "";
   exit;
  }
 }
  private function receiveEvent($object){
   $content = "";
   switch ($postObj->Event){
    case "subscribe":
    $content = "欢迎关注网志博客";//这里是向关注者发送的提示信息
    break;
    case "unsubscribe":
    $content = "";
    break;
   }
   $result = $this->transmitText($object,$content);
   return $result;
    }
 private function transmitText($object,$content){
   $textTpl = "
      
      
       %s
      
      
       0
       ";
    $result = sprintf($textTpl, $object->FromUserName, $object->$ToUserName, time(), $content);
    return $result;
  }
 private function checkSignature()
 {
  $signature = $_GET["signature"];
  $timestamp = $_GET["timestamp"];
  $nonce = $_GET["nonce"];
  $token = TOKEN;
  $tmpArr = array($token, $timestamp, $nonce);
  sort($tmpArr, SORT_STRING);
  $tmpStr = implode( $tmpArr );
  $tmpStr = sha1( $tmpStr );
  if( $tmpStr == $signature ){
   return true;
  }else{
   return false;
  }
 }
}

代码相关参数说明: