注意：会话中的未定义索引[重复]

I having this error Notice: Undefined index: uid_fb

please help

<?php 
include "common.php";
if($_SESSION['uid_fb']!='' && $_SESSION['login_fb']=='true')
{
// header("Location:home.php"); 
}

</div>

<?php 
   include "common.php";
   if (!empty($_SESSION['uid_fb']) &&
        isset($_SESSION['login_fb']) &&
        $_SESSION['login_fb']=='true')
   {
      // ...
   }

Use isset to determine if a variable has a value. Use empty to determine if a variable is not set, or empty.

Add isset:

<?php 
include "common.php";
if(isset($_SESSION['uid_fb']) && $_SESSION['uid_fb']!='' && $_SESSION['login_fb']=='true')
{
// header("Location:home.php"); 
}