What does render() do in Zend Framework - zend-framework

Question

This is another of those utilities where every blogger\tutor assumes we all know what it is, therefore they never bother to explain what it actually does. They just go on to use it in their examples, believing we all know what's going on.
From how people use or refer to render(), it would suggest that it displays content(eg: view content) but if this is so, then why do we use echo to actually display it's content?
Other uses suggests that it formats content, as used in form-decorators where internally we employ sprintf() to inject variables into strings.
So what does render() do in cases like Zend_View, Zend_Layout, etc? Can someone please explain it's workings on a fundamental level(under the hood). Thanks.

Answer 1

It loads a view script and outputs it as a string.
Simplifying a bit, Zend_View takes a view script file (like index.phtml) and includes it internally to produce the HTML output. By using the render() method, it's possible to take an additional view script (like maybe nav.phtml) and output it inside your parent view script. The idea is to render elements that are repeated on many pages just one single time instead of repeating the same HTML over and over again.
The code for the render method can be found in the Zend_View_Abstract class and is the following:
/**
* Processes a view script and returns the output.
*
* #param string $name The script name to process.
* #return string The script output.
*/
public function render($name)
{
// find the script file name using the parent private method
$this->_file = $this->_script($name);
unset($name); // remove $name from local scope
ob_start();
$this->_run($this->_file);
return $this->_filter(ob_get_clean()); // filter output
}
The implementation of the _run() method can be found in the class Zend_View and is the following:
/**
* Includes the view script in a scope with only public $this variables.
*
* #param string The view script to execute.
*/
protected function _run()
{
if ($this->_useViewStream && $this->useStreamWrapper()) {
include 'zend.view://' . func_get_arg(0);
} else {
include func_get_arg(0);
}
}
As you can see, render() takes a view script name, resolves its file name, initiates output buffering, includes the view script file (this is what the _run() method does internally), then passes the output through optional filters and finally returns the generated string.
The neat thing about it is that it retains the properties (variables) of the view object it is called from (because it's the same Zend_View object, just with a different view script loaded). In this respect, it differs from the partial() method, which has its own variable scope and you can pass variables into it (making it useful for rendering smaller elements, such as single rows of data when you foreach over a dataset).