run php function when order complete

Question

I'm new to magento and i don't have any idea about how I can run specific PHP function when user order completion.
can anyone explain me how I can do this?
I read about event/observer but I don't understand how to use
Thanks

Answer 1

An "observer" is a fancy name for a method on a class definition that is executed on an event. Any number of observers can be fired for any one event.

To create one you first create a module. In the module config.xml definition locate (or create) the <global>, <frontend> and <adminhtml> nodes. You can create the event listener in any one of those 3 nodes. To register it, do the following:

<events>
    <event_name_here>
        <observers>
            <store>
                <class>yourmodule/observer</class>
                <method>methodName</method>
            </store>
        </observers>
    </event_name_here>
</events>

To get a list of valid event names you can visit this site here.

In your module, create a class file called Observer.php in the Model directory. It will look something like:

class YourCompany_YourModule_Model_Observer
{
    public function methodName($observer)
    {
        //observer data is in $observer->getEvent()
    }
}

From there, whenever the event name you're listening to is called, your module's Observer model will be loaded and the method you've registered will fire.