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Understanding the view rendering flow
Difference between #11 and #10 of Understanding the view rendering flow
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FAQs
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layouts, views, render, renderPartial, variables, beginContent, understanding
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Introduction ------------------ There arelot ofmany confusionsaboutregarding what is happening behind thescenescenes when you renderthea view. If we take a look at the blog demo we have 3 major parts of our view rendering and they are: **1)** The layouts/column1 and column2 thatlookslook like (column1.php and column2.php): ~~~ [php] <?php $this->beginContent('/layouts/main'); ?> <div class="container"> <div id="content"> <?php echo $content; ?> </div><!-- content --> </div> <?php $this->endContent(); ?> ~~~ **2)** We have layouts/main ~~~ [php] <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta name="language" content="en" /> <!-- blueprint CSS framework --> <link rel="stylesheet" type="text/css" href="<?php echo Yii::app()->request->baseUrl; ?>/css/screen.css" media="screen, projection" /> <!-- some more headers... --> <title><?php echo CHtml::encode($this->pageTitle); ?></title> </head> <body> <!-- ... --> <?php $this->widget('zii.widgets.CBreadcrumbs', array( 'links'=>$this->breadcrumbs, )); ?><!-- breadcrumbs --> <?php echo $content; ?> </body> </html> ~~~ **3)** and the view that we render , for example site/contact ~~~ [php] <?php $this->pageTitle=Yii::app()->name . ' - Contact Us'; $this->breadcrumbs=array( 'Contact', ); ?> <h1>Contact Us</h1> <!-- ... --> ~~~ The call to the view rendering in the contact looks like the following:- ~~~ [php] /** * Displays the contact page */ public function actionContact() { $model=new ContactForm; //some form code was here... $this->render('contact',array('model'=>$model)); } ~~~ <center>  </center> The common questions andconfusions:confusions we will address: ---------------------------- **1)**whatWhy if I pass the contact some $test variable like $this->render('contact',array('model'=>$model,'test' => 123));Andand I echo it in the layout with echo $test, I get error 500 undefind variable error? **2)** I didn'tpassedpass any $content variable so what is ~~~ [php] <?php echo $content; ?> ~~~insidedoing inside the beginContent tagsinsideof column1.php ? **3)** Why does the layouts/main.phphashave ~~~ [php] <?php echo $content; ?> ~~~Don't passedI didn't pass such variable... **4)** Why do both column1.php and main.php echo the $content ? **5)**What if I changeWhy does setting the title insidecontact.php, does itcontact.php change the variable $this->titleinside thein main.php? ~~~ [php] <title><?php echo CHtml::encode($this->pageTitle); ?></title> /* in contact.php $this->pageTitle=Yii::app()->name . ' - Contact Us'; */ ~~~ #### And the main confusion: **6)**whatWhat is called before what?whatWhat the heck is going on there ? ;-) <center>  </center> Diving in the source code ------------------------- You have two options:<br> **1)** You can accept the rules and follow them without understanding<br> **2)** You can understand and follow the rules... If you choose number 1, tutorial is over for you ;-) But if you really want to learn and understand,letslet's dive together... <center>  </center> Every good IDE has the ability to go directly to the function by pressing ctrl andthan thethe function name... So lets go to SiteController.php, to the actionContact and press the render wordinat this line: ~~~ [php] $this->render('contact',array('model'=>$model)); ~~~ After pressing you will find yourself inside yii/web/CController.php on line 775 ~~~ [php] public function render($view,$data=null,$return=false) { if($this->beforeRender($view)) { $output=$this->renderPartial($view,$data,true); if(($layoutFile=$this->getLayoutFile($this->layout))!==false) $output=$this->renderFile($layoutFile,array('content'=>$output),true); $this->afterRender($view,$output); $output=$this->processOutput($output); if($return) return $output; else echo $output; } } ~~~ The rendering is starting with a call to beforeRender, This is a preprocessing, if we are talking about the blog demo, no preprocessing there, so it just returns true... ~~~ [php] protected function beforeRender($view) { return true; } ~~~ After we got true, we can continue ... We have, ~~~ [php] $output=$this->renderPartial($view,$data,true); ~~~ So our 'contact' view is rendered partially, with third parameter as true, this means that the result is not echoed to the page, it is captured and passed to the $output variable... At this stage the contact page is rendered, all the $data it got (the variable array) is passed to the view was processed After this, if a layout is defined ~~~ [php] if(($layoutFile=$this->getLayoutFile($this->layout))!==false) $output=$this->renderFile($layoutFile,array('content'=>$output),true); ~~~ we pass the $output we captured from the contact.php file, and pass it as $content to our layout file column1.php Also this time the third parameter is true, meaning we done echo the output, we capture it and pass to $output variable (at this point the view output is overwritten, we don't need it any more cause we passed it to the view and it processed). After this the afterRender called, and the processOutput, it's role is to insert all the javascript css etc. we registered as client scripts etc. <center>  </center> Time for answers ---------------- After we followed all the life cycle of the render method, we can answer to all the questions... **1)** why if I pass to the contact some $test variable like $this->render('contact',array('model'=>$model,'test' => 123)); And I echo it in the layout with echo $test, I get error 500 undefind variable error? **Answer:** Because the parameters we pass to the $this->render method, are processed in the view file , in this example contact.php, and then we pass to the layout the generated view, and the variable $test is out of the scope for hte layout. What to do if you need it? you can use the Yii registry(params), or you can define some class field, or consider creating widget ... (depends on the task) **2)** I dont passed any $content variable so what is ~~~ [php] <?php echo $content; ?> ~~~ Inside the beginContent tags inside column1.php ? **Answer:** the captured view is passed to the layout as content parameter **3)** Why the layouts/main.php has ~~~ [php] <?php echo $content; ?> ~~~ Don't passed such variable... **Answer:** ~~~ [php] <?php $this->beginContent('//layouts/main'); //... $this->endContent(); ~~~ All what between beginContent and endContent, is captured and passed to the layouts/main as content variable... **4)** Why both column1.php and main.php echo the $content ? **Answer:** If you understood answers to 1-3, you know the answer for this one... they are not the same, and don't have the same value **5)** why if I change inside contant.php the title, it changes the main.php $this->title variable ? ~~~ [php] <title><?php echo CHtml::encode($this->pageTitle); ?></title> /* in contact.php $this->pageTitle=Yii::app()->name . ' - Contact Us'; */ ~~~ **Answer:** as we saw, the contact.php is rendered before the layout, so every field( aka class parameters), you change from the view file (contact.php) will effect the layout because it rendered after... #### And the main confusion: **6)** what is called before what? what the heck is going on there ? ;-) <center> **contact.php (passed as content)-> column1.php (passed as content)-> main.php** </center> <center> <img src="http://i30.fastpic.ru/big/2011/1007/21/6c07cda81e332dba19bd59a812abc121.png" width="750"/></center> That's it, now you pro in layouts ;-)
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- Written by: dckurushin
- Updated by: Jorgee
- Category: FAQs
- Votes: +65 / -1
- Viewed: 67,784 times
- Created on: Oct 7, 2011
- Last updated: Apr 15, 2013
- Tags: layouts, views, render, renderPartial, variables, beginContent, understanding