silverstripe init() function - php

Question

Can someone explain this code in Silverstripe:
public function init() {
RSSFeed::linkToFeed($this->Link() . "rss");
parent::init();
}
What exactly is init function?
what parent::init();
exactly do in code

Answer 1

in php classes when you overwrite a method of parent class you still can call the parent class with this code, it will help you to put some code at the beginning of the real method without removing it.
you can find out more about it at php documentation

Answer 2

The upmost init() method is defined in the Controller class.
Then ContentController extends Controller, which overrides the Controller class's init() method, but it's also calling parent::init() on the first line. Then usually you define all your page controller classes like this (for any new page type), in the example below for the default Page_Controller class:
class Page_Controller extends ContentController {
public function init() {
parent::init();
// do your own stuff here
}
}
So this is the traditional PHP based class extension mechanism, but Silverstripe also allows you to use Extensions and Data Extensions, which is basically extending the functionality of already existing controllers, data objects. I won't go into details with this... You can find out more about this here: https://docs.silverstripe.org/en/4/developer_guides/extending/extensions/
I usually have something like this in my controller classes:
class Page_Controller extends ContentController {
public function init() {
parent::init();
// do your own stuff here
$this->extend('updateInit');
}
}
Notice the $this->extend('updateInit'); line above.
I can have another extension defined for the Page_Controller class inside a YAML config file somewhere, and than have the updateInit() method defined in that class. Example:
class Page_Controller_Extension extends Extension {
public function updateInit() {
// do some more stuff here
}
}
...and in this case you would have something like this in a YAML config file:
---
Name: siteextensions
After:
- 'framework/*'
- 'cms/*'
---
Page_Controller:
extensions:
- Page_Controller_Extension
Note that this is not really the traditional way of extending classes, like in PHP, it's more like defining some decorators for a controller class. Also, to refer to the parent, or object being decorated, you can't use just $this, you'll need to use $this->owner. Example below:
class Page_Controller_Extension extends Extension {
public function updateInit() {
// do some more stuff here
if ($this->owner->IsFeatured) {
// do something here
}
}
}
You usually decorate controllers extending the Extension class, and you extend the DataExtension class if you want to decorate DataObjects - works the same way as explained above.