Event Messaging in ZXAF

Event Messaging in ZXAF admin 9 November, 2009 - 15:30

The hardest thing to grasp completely with ZXAF is probably the way that the inter object communications can be used.

The easiest way of showing this is to refer to views/view-main.php, search for GlobalEventBus::notify_all and you will see many occurrences. Each one of these messages sent is really related to the standard stuff that you need to be in the page container. The beauty of the event notifications is that the view module does not concern itself with how the message is handled, all it knows is that someone, somewhere will receive the message and do the right thing with it.

This is important because it decouples view-main from the WebPage container, it frees view-main from specific chunks of code related to templates.

The other benefit is that the recipient can manage the messages as they come in, for example when using the following to request the inclusion of a javascript module:

GlobalEventBus::notify_all(new MessageRegisterJavascript(MessageRegisterJavascript::Type_Script, "javascripts/jquery.timeentry.js"));

It is the recipient that can decide to only do this once, so each object within view-main doesn't need to worry if that script has already been included it can simply state that it needs the module included, and be confident that it will be included

Another example is the callback processing during an Ajax update. The objects in view-main don't need to be concerned at how the updated HTML will be fed to back to the browser, all they need to do is to create the HTML together with the identifying key (id) and send a message as follows:

GlobalEventBus::notify_all(new MessageAjaxUpdate($key, $html));


Upon receipt the WebPage can store this, and later on during the processing it will convert this into JSON, output it and exit, because the WebPage knows that this is the right action, whereas the objects in view-main do not need to have this logic wired in.

As said at the beginning this is a hard concept to really grasp, and these worked examples on start to demonstrate the power that can be harnessed from this technique