Facebook 2008 FBML Guida Utente Scaricare il pdf (Pagina 152)

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firedByDescription.setTextValue('');

return true;

}

//otherwise... do some processing:

//*VERY IMPORTANT*: note that the object, which fired the event is located two nodes up in the DOM tree

//See note below

//eventFiredBy_ObjectId = evt.target.getParentNode().getParentNode().getId();

//On newer versions, it seems that there is no need to go up two levels int he DOM tree, hence

eventFiredBy_ObjectId = evt.target.getId();

//works, whereas the first does not!

//**NOTE** My testing of this suggests that when you call addEventListener() it adds it to the element, AND

all it's descendants

// This can then cause the event to be fired multiple times, as it is fired for the element and it's descendant

elements.

// When fired by a descendant element, you will probably have to do some kind of getParent()-ing

// I'm raising this as a bug, as it does make things a little unworkable!

//once you have the ID, you may, for example, drop its id into the firedByDescription div:

firedByDescription.setTextValue(eventFiredBy_ObjectId);

//... or do some conditional processing:

if (eventFiredBy_ObjectId == 'foo') {

//do something if the event was fired by 'foo'

} else {

//do something if the event was fired by 'bar'

}

//add event listener to 'foo' div (mouseover & mouseout)

document.getElementById('foo').addEventListener('mouseover',myEventHandler);

document.getElementById('foo').addEventListener('mouseout',myEventHandler);

//add *the same* event listener to 'bar' div (mouseover & mouseout)

document.getElementById('bar').addEventListener('mouseover',myEventHandler);

document.getElementById('bar').addEventListener('mouseout',myEventHandler);

</script>

This functionality is very useful in cases where you have one event handler for multiple objects of the same

type. Take for instance a shopping cart of some sort, or any type of object browser. When a user moves her

mouse over one of the items in the cart, you may want to conditionally display information about the item -- by

finding its ID, you may associate a description text for that item and display it to the user in another div. As you

can see, using event listeners can be a very powerful way to display useful additional information to the user,

based on where they move their mouse within your Facebook application. Happy coding and creativity!

www.yapish.com

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Facebook 2008 FBML Guida Utente Pagina 152