Dynamically add links to 'my account navigation' in magento

Question

I'm creating a Magento Extension and want to be programatically add links to the 'My account' navigation. I've read the following thread (Magento - How to add/remove links on my account navigation?) and the sites it references, but they only talk about adding a link statically.

By adding the following to a layout file in my module I can get a new link to appear in the customer account navigation.

<customer_account>
    <reference name="customer_account_navigation">
        <action method="addLink" translate="label" module="mymodule">
            <name>modulename</name>
            <path>mymodule/</path>
            <label>New link</label>
        </action>
    </reference>
</customer_account>

How can I make it so that this links appearance depends on the results of a method call to one of my extensions models.

Answer 1

You have to use event-observer functionality of magento The event you have to use it "controller_action_layout_load_before" In your module's config.xml

<controller_action_layout_load_before>
    <observers>
        <uniquename>
            <type>singleton</type>
            <class>Package_Modulename_Model_Observer</class>
            <method>customlink</method>
        </uniquename>
    </observers>
</controller_action_layout_load_before>

and in the corresponding observer.php use the following code

public function customlink(Varien_Event_Observer $observer)
{
    $update = $observer->getEvent()->getLayout()->getUpdate();
    $update->addHandle('customer_new_handle');
}

and in local.xml write

<customer_new_handle>
    <reference name="customer_account_navigation">
        <action method="addLink" translate="label" module="mymodule">
            <name>modulename</name>
            <path>mymodule/</path>
            <label>New link</label>
        </action>
    </reference>
</customer_new_handle>