Event Handlers

Last updated 4 months ago

Event handlers are ColdBox's version of controllers in the MVC design pattern. So every time you hear "event handler", you are talking about a controller that can listen to external events or internal events in ColdBox. These event handlers carry the task of controlling your application flow, calling business logic, preparing a display to a user and much more.

Locations

All your handlers will go in the handlers folder of your application template. If you get to the point where your application needs even more decoupling and separation, please consider building ColdBox Modules instead.

Tip: You can create packages or sub-folders inside of the handlers directory. This is encouraged on large applications so you can section off or package handlers logically and get better maintenance and URL experience.

External Location

You can also declare a HandlersExternalLocation directive in your Configuration CFC. This will be a dot notation path or instantiation path where more external event handlers can be found.

coldbox.handlersExternalLocation = "shared.myapp.handlers";

If an external event handler has the same name as an internal conventions event, the internal conventions event will take precedence.

Development Settings

By default, ColdBox will only scan for event handlers on startup. For development we highly encourage you leverage the following configuration directives:

// Rescan handlers on each request, turn OFF in production please
coldbox.handlersIndexAutoReload = true;
// Deactivate singleton caching of the handlers, turn ON in production pleaese
coldbox.handlerCaching = false;

Anatomy

Event handlers are CFCs that will respond to FORM posts, HTTP requests and/or remote requests (like Flex,Air, SOAP, REST) via an incoming variables called event or by URL mappings (Which we saw in the previous section).

Components

Main.cfc
component extends="coldbox.system.EventHandler"{
/**
* Default Action
*/
function index( event, rc, prc ){
prc.message = "Hello From ColdBox";
event.setView( "main/index");
}
/**
* Action returning complex data, converted to JSON automatically by ColdBox
*/
function data( event, rc, prc ){
var data = getInstance( "MyModel" ).getArray();
return data;
}
}

You can also remove the inheritance from the CFC and WireBox will extend the coldbox.system.EventHandler for you using Virtual Inheritance.

Event Handlers are treated as singletons by ColdBox, so make sure you make them thread-safe and properly scoped. Persistence is controlled by the coldbox.handlerCaching directive

Actions

They are composed of functions which are called actions that will always have the following signature:

function name( event, rc, prc )

Each action receives three arguments:

  1. event - An object that models and is used to work with the current request

  2. rc - A struct that contains both URL/FORM variables (unsafe data)

  3. prc - A secondary struct that is private only settable from within your application (safe data)

An action will usually do the following:

  • Set a view/layout to render

  • Return HTML

  • Return Complex Data which is converted to JSON by default

  • Relocate to another event/URL Route

The default action for all event handlers is called index(). This means that when you execute an event, you can omit the index if you so desire.

component extends="coldbox.system.EventHandler"{
function index( event, rc, prc ){
return "<h1> Hi from handler land!</h1>";
}
function save( event, rc, prc ){
getInstance( "MyService" ).save( rc );
relocate( "users/list" );
}
function myData( event, rc, prc ){
return ['coldbox', 'wirebox', 'cachebox', 'logbox'];
}
}

Private Actions

So what about private functions? Private functions are not executable from the outside world, but can be executed internally via a function available to all handlers called runEvent(), which we will explore later.

Composed Properties

It is imperative that you realize that there is a great object model behind every event handler controller that will enable you to do your work more efficiently. The following are the composed properties every event handler has in their variables scope, you do not need to do anything to retrieve them, they are already there :)

Event Handler UML
  • cachebox : A reference to the CacheBox library (coldbox.system.cache.CacheFactory)

  • controller : A reference to the Application Controller (coldbox.system.web.Controller)

  • flash: A flash memory object (coldbox.system.web.flash.AbstractFlashScope)

  • logbox: A reference to the application LogBox (coldbox.system.logging.LogBox)

  • log: A pre-configured logging logger object (coldbox.system.logging.Logger)

  • wirebox : A reference to the application WireBox Injector (coldbox.system.ioc.Injector)

  • $super: A reference to the virtual super class if using non-inheritance approach.