PHP:Invalid argument supplied for foreach 解决办法

Warning: Invalid argument supplied for foreach() 
问题Warning: Invalid argument supplied for foreach() in 完善解决方案
将报错的语句做如下修改（例）：
把

QUOTE:
foreach($extcredits as $id => $credit) 
{
         if($credit['ratio']) 
         {
                 $exchcredits[$id] = $credit;
         }
}
改为

QUOTE:
if(is_array($extcredits))    //add
{                           
         foreach($extcredits as $id => $credit) 
         {
                  if($credit['ratio']) 
                  {
                              $exchcredits[$id] = $credit;
                  }         
        }
}   //add
或

QUOTE:
foreach((array)$extcredits as $id => $credit) 
{
         if($credit['ratio']) 
         {
                 $exchcredits[$id] = $credit;
         }
}