Creating Hello world event dispatcher(observer) in Magento?

I am trying to create an event dispatcher in Magento (which should be called after a product gets added to cart).

What I've done so far:

I Googled this and found this link. I followed the instructions specified in this link. I configured the config.xml file and created a Observer.php filder under mymodule/model folder. But, I can't see any result from this.

(The code for config.xml and Observer.php file that i used in my example can be found under http://goo.gl/O7dBy, my custom module name is Crossdata and package name is MyModule - am i doing it wrong?)

Any other link with simple helloworld event dispatcher example would be helpful.

Thanks, Balan

Looking at your code you define:

<events>
    <add_to_cart_after>
        <observers>
            <add_to_cart_after>
                <class>dispatcher/observer</class>
                <method>hookToAddToCartAfter</method>
            </add_to_cart_after>
        </observers>
    </add_to_cart_after>
</events>

and define the model alias of dispatcher as:

<models>
    <dispatcher>
        <class>MyPackage_Crossdata_Dispatcher_Model</class>
    </dispatcher>
</models>

The resulting class name would be MyPackage_Crossdata_Model_Dispatcher_Model_Observer, but your observer class is named MyPackage_Crossdata_Dispatcher_Model_Observer, missing the Model in between Crossdata and Dispatcher.

I'd recommend to drop the whole dispatcher models definition above and only use the other model alias crossdata which you've already defined in config.xml:

<crossdata>
    <class>MyPackage_Crossdata_Model</class>
    <resourceModel>crossdata_mysql4</resourceModel>
</crossdata>   

Then change the event definition to:

<add_to_cart_after>
    <class>crossdata/observer</class>
    <method>hookToAddToCartAfter</method>
</add_to_cart_after>

Create a file /app/code/local/MyPackage/Crossdata/Model/Observer.php and define your observer class in it:

class MyPackage_Crossdata_Model_Observer
{
    public function hookToAddToCartAfter($observer)
    {
        // your observer code
    }
}