ZF2: How to pass a variable from the method attached to MvcEvent::EVENT_FINISH to the layout attached in MvcEvent::EVENT_RENDER? - zend-framework2

Question

I am trying to understand Zend Framework 2 (ZF2). Few days ago I bought the book "Learn ZF2: Learning By Example" by Slavey Karadzhov. Now I am reading it and trying to get some examples working.
I am stuck in page 60. The example shown in the book works well, but the modification I just made does not work... Why? How to fix it?
To get into the same code/situation you would have to:
git clone https://github.com/slaff/learnzf2 .
composer.phar self-update
composer.phar install
git stash
git checkout 'ch-view'
After that You will have the same setup as I do.
Now I have changed the file /module/Debug/view/debug/layout/sidebar.phtml from this:
<h1>Top Line</h1>
<?= $this->content ?>
<h1>Bottom Line</h1>
to this (just added one line at the end):
<h1>Top Line</h1>
<?= $this->content ?>
<h1>Bottom Line</h1>
<p>MVC duration: <?= $this->mvcDuration ?></p>
I would like $this->mvcDuration to be the value of $duration from /module/Debug/Module.php file getMvcDuration method.
I changed the content of method getMvcDuration from this:
public function getMvcDuration(MvcEvent $event)
{
// Here we get the service manager
$serviceManager = $event->getApplication()->getServiceManager();
// Get the already created instance of our timer service
$timer = $serviceManager->get('timer');
$duration = $timer->stop('mvc-execution');
// and finally print the duration
error_log("MVC Duration:".$duration." seconds");
}
to this (added two lines at the end of the method):
public function getMvcDuration(MvcEvent $event)
{
// Here we get the service manager
$serviceManager = $event->getApplication()->getServiceManager();
// Get the already created instance of our timer service
$timer = $serviceManager->get('timer');
$duration = $timer->stop('mvc-execution');
// and finally print the duration
error_log("MVC Duration:".$duration." seconds");
$viewModel = $event->getViewModel();
$viewModel->setVariable('mvcDuration', $duration);
}
However, this kind of change does not work and the value of $duration is not passed to the layout. The question is WHY? How can I pass $duration to $this->mvcDuration of the layout?
p.s. The code downloaded from official github repo (https://github.com/slaff/learnzf2) is acting quite strange... Changing project files (e.g.: /module/Debug/view/debug/layout/sidebar.phtml) does not change the output. If You have the same situation while trying to help me with this case then I would suggest you to modify files in /vendor/learnzf2 directory instead of files in /module directory. I know that modifying code in vendor directory is not good thing to do, but let this post (my question) be about the one problem only.

Answer 1

Good book. Your basic problem is that you are Trying to update a variable into the view in a method that is triggered after the view has already been sent. You probably can't do this, unless you redefine which event triggers it, but that would defeat the intended purpose of timing the whole mvc duration.
All that said, you shouldn't be injecting variables into the view model from module.php. It's very hard to test that. This is what view helpers are good for.