Re: Overriding/Extending cgiapp_postrun()

On Wed, 17 Nov 2004 09:20:43 -0600, Jason A. Crome <crome@xxxxxxxxxxxxx> wrote:
> So I am getting a little fancier with my CGI::Applications these days. . .
> I'm using inheritance to cut down the amount of duplicate code and
> maintenance hassles I created for myself.  I'm having some issues extending
> the functionality of cgiapp_postrun() however.  Allow me to explain my
> intent a bit:
> 
<snip - base object's cgiapp_postrun>
> 
> So I threw this code in my base object (let's call it My::App) and it works
> great!
> 
> I have an instance now where an app derived from My::App wants to process
> the output of one of it's runmodes before the base object processes it.  The
> code for this looks like:
> 
> sub cgiapp_postrun
> {
>     my $self     = shift;
>     my $html_ref = shift;
> 
>     # Drop out if we are printing a tax statement
>     return if $self->get_current_runmode() eq "print";
> 
>     # Dereference the output data
>     my $html = $$html_ref;
> 
>     # Draw the tab page
>     my $tabs = $self->draw_tabs($html);
> 
>     # Replace old page with the new one
>     $$html_ref = $tabs;
> 
>     # Invoke our ancestor's functionality
>     $self->SUPER::cgiapp_postrun(\$tabs);
> }
> 
> And for a reason I can't explain, it seems as if the output in the base
> object is completely ignored.  I know it's being called, because if I throw
> a die() in there, the app does in fact die.  But the output of the runmode
> isn't displayed.  What am I doing wrong?  I've been staring at this a while
> and I have the feeling something simple is glaring at me.  I just can't see
> it.

The issue is that you're passing a different reference to the base class
than is getting passed to the child class:
      
      # Invoke our ancestor's functionality
      $self->SUPER::cgiapp_postrun(\$tabs);

run() passes a reference to cgiapp_postrun(), but doesn't expect
anything returned. After the cgiapp_postrun() method has finished, run()
basically spits out the reference as the page output. So, what I see
happening is that your child class grabs the reference into $html_ref,
which gets modified... but then you pass a reference to $tabs to the
parent class' cgiapp_postrun(). $html_ref never gets changed by the
parent class, in that situation.

Easy fix: pass $html_ref to the parent's cgiapp_postrun().

-- 
Matthew Weier O'Phinney
mweierophinney@xxxxxxxxx
http://weierophinney.net/matthew/

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