I recently had a report from a user that many of the pages within the wp-SwimTeam plugin were blank.  This is odd and incorrect behavior but I have seen it before.  When I last chased it down I found that the way various versions of PHP 5.2.x and 5.3.x handled Constructors was different and in some versions Constructors in parent classes would be called and in some versions they wouldn’t.

I assumed this new report of blank pages meant that I had missed one of these Constructor issues somewhere.  It turns out that wasn’t the case.  This time I found that PHP’s method_exists() function behaves differently between different versions of PHP on different platforms.

The report came in from a site running PHP 5.3.13 which is the same as what I am running in my development area.  The only difference I can see between the two servers is mine is running on Windows under IIS where as the problematic site is running Apache under Linux.

When a page is rendered for wp-SwimTeam, the objects on the page are traversed and HTML code is generated.  The objects which comprise the page content can either be strings (HTML code) or objects themselves which then traversed recursively until all of the leaf HTML is assembled.  This is core functionality in phpHtmlLib that I have been using for years without any issues until now.

What I found was that if the variable passed to method_exists() was a string instead of an object, PHP goes out in the weeds and never returns which ultimately results in the blank page.  This is the code that has been rendering objects in phpHtmlLib for 10+ years:

if (method_exists($item, "render") ) {

It was fairly simple to fix it.  By checking to see if the item is an object prior to checking for it’s render method, the problem is resolves and the page renders correctly.

if (is_object($item) && method_exists($item, "render") ) {

I will be updating phpHtmlLib with this fix shortly.