Preside viewlets


Coldbox has a concept of viewlets (see what they have to say about it in their docs).

Preside builds on this concept and provides a concrete implementation with the renderViewlet() method. This implementation is used throughout Preside and is an important concept to grok when building custom Preside functionality (widgets, form controls, etc.).

The Coldbox Viewlet Concept

Conceptually, a Coldbox viewlet is a self contained module of code that will render some view code after performing handler logic to fetch data. The implementation of a Coldbox viewlet is simply a private handler action that returns the rendered view (the handler must render the view itself). This action will be directly called using the runEvent() method. For example, the handler action might look like this:

private any function myViewlet( event, rc, prc, id=0 ) {
    prc.someData = getModel( "someService" ).getSomeData( );
    return getPlugin( "renderer" ).renderView( "/my/viewlets/view" );

And you could render that viewlet like so:

#runEvent( event="SomeHandler.myViewlet", prePostExempt=true, private=true, eventArguments={ id=2454 } )#

The Preside renderViewlet() method

Preside provides a concrete implementation of viewlets with the renderViewlet() method. For the most part, this is simply a wrapper to runEvent() with a clearer name, but it also has some other differences to be aware of:

  1. If the passed event does not exist as a handler action, renderViewlet() will try to find and render the corresponding view
  2. It defaults the prePostExempt and private arguments to true (this is the usual recommended behaviour for viewlets)
  3. It formalizes how viewlet arguments are passed to the handler / view. When passing arguments to a handler action or view, those arguments will be available directly in the args structure

Example viewlet handler

Below is an example of a Preside viewlet handler action. It is much the same as the standard Coldbox viewlet handler action but receives an additional args structure that it can make use of and also passes any data that it gathers directly to the view rather than relying on the prc / rc (this is recommendation for Preside viewlets).

private any function myViewlet( event, rc, prc, args={} ) {
    args.someData = getModel( "someService" ).getSomeData( id=( ?: 0 ) );
    return getPlugin( "renderer" ).renderView( view="/my/viewlets/view", args=args );

You could then render the viewlet with:

#renderViewlet( event="SomeHandler.myViewlet", args={ id=5245 } )#

Example viewlet without a handler (just a view)

Sometimes you will implement viewlets in Preside without a handler. You might find yourself doing this for custom form controls or widgets (which are implemented as viewlets). For example:

<cfparam name="args.title" type="string" /> 
<cfparam name="args.description" type="string" />

Rendering the viewlet:

#renderViewlet( event="viewlets.myViewlet", args={ title="hello", description="world" } )#


The renderViewlet() method is available to your handlers and views directly. In any other code, you will need to use getController().renderViewlet() where getController() would return the Coldbox controller instance. It takes the following arguments:

Argument Type Required Description
event string Yes Coldbox event string, e.g. "mymodule:myHandler.myAction"
args struct No A structure of arguments to be passed to the viewlet
prePostExempt boolean No Whether or not pre and post events should be fired when running the handler action for the viewlet
private boolean No Whether or not the handler action for the viewlet is a private method