Components: Events

Available from Prado versions 3.2.3 onwards.

Component events

An event is defined by the presence of a method whose name starts with on. The event name is the method name and is thus case-insensitive. An event can be attached with one or several methods (called event handlers). An event can be raised by calling raiseEvent method, upon which the attached event handlers will be invoked automatically in the order they are attached to the event. Event handlers must have the following signature,

function eventHandlerFuncName($sender, $param) { ... }

where $sender refers to the object who is responsible for the raising of the event, and $param refers to a structure that may contain event-specific information. To raise an event (assuming named as 'Click') of a component, use

$component->raiseEvent('OnClick', $this, $param);

To attach an event handler to an event, use one of the following ways,

$component->OnClick = $callback;
$component->attachEventHandler('OnClick', $callback);

The first two ways make use of the fact that $component->OnClick refers to the event handler list TWeakCallableCollection for the 'OnClick' event. The variable $callback contains the definition of the event handler that can be either:

  • a string referring to a global function name
  • $component->OnClick = 'buttonClicked';
    // will cause the following function to be called
    buttonClicked($sender, $param);
  • an array whose first element refers to an object and second element a method name/path that is reachable by the object
    $component->OnClick = [$object, 'buttonClicked'];
    // will cause the following function to be called
    $object->buttonClicked($sender, param);
    // the method can also be expressed using the PRADO namespace format
    $component->OnClick = [$object, 'MainContent.SubmitButton.buttonClicked'];
    // will cause the following function to be called
    $object->MainContent->SubmitButton->buttonClicked($sender, $param);

Global events

With the addition of behaviors, a more expansive event model is needed. There are two new event types (global and dynamic events) as well as a more comprehensive behavior model that includes class wide behaviors.

A global event is defined by all events whose name starts with fx. The event name is potentially a method name and is thus case-insensitive. All fx events are valid as the whole fx event/method space is global in nature. Any object may patch into any global event by defining that event as a method. Global events have priorities just like 'on' events; so as to be able to order the event execution. Due to the nature of all events which start with fx being valid, in effect, every object has every fx global event. It is simply an issue of tapping into the desired global event.

A global event that starts with fx can be called even if the object does not implement the method of the global event. A call to a non-existing fx method will, at minimal, function and return null. If a method argument list has a first parameter, it will be returned instead of null. This allows filtering and chaining. fx methods do not automatically install and uninstall. To install and uninstall an object's global event listeners, call the object's listen and unlisten methods, respectively. An object may auto-install its global event during __construct by overriding getAutoGlobalListen and returning true.

As of PHP version 5.3, nulled objects without code references will still continue to persist in the global event queue because __destruct is not automatically called. In the common __destruct method, if an object is listening to global events, then unlisten is called. unlisten is required to be manually called before an object is left without references if it is currently listening to any global events. This includes class wide behaviors. This is corrected in PHP 7.4.0 with WeakReferences and TWeakCallableCollection.

An object that contains a method that starts with fx will have those functions automatically receive those events of the same name after listen is called on the object.

An object may listen to a global event without defining an fx method of the same name by adding an object method to the global event list. For example

$component->fxGlobalCheck = $callback;
$component->attachEventHandler('fxGlobalCheck', [$object, 'someMethod']);

Events between Objects and their behaviors, Dynamic Events

An intra-object/behavior event is defined by methods that start with dy. Just as with fx global events, every object has every dynamic event. Any call to a method that starts with dy will be handled, regardless of whether it is implemented. These events are for communicating with attached behaviors.

Dynamic events can be used in a variety of ways. They can be used to tell behaviors when a non-behavior method is called. Dynamic events could be used as data filters. They could also be used to specify when a piece of code is to be run, eg. should the loop process be performed on a particular piece of data. In this way, some control is handed to the behaviors over the process and/or data.

If there are no handlers for an fx or dy event, it will return the first parameter of the argument list. If there are no arguments, these events will return null. If there are handlers an fx method will be called directly within the object. Global fx events are triggered by calling raiseEvent. For dynamic events where there are behaviors that respond to the dynamic events, a TCallChain is developed. A call chain allows the behavior dynamic event implementations to call further implementing behaviors within a chain.

If an object implements IDynamicMethods, all global and object dynamic events will be sent to __dycall. In the case of global events, all global events will trigger this method. In the case of behaviors, all undefined dynamic events which are called will be passed through to this method.


There are two types of behaviors. There are individual object behaviors and there are class wide behaviors. Class behaviors depend upon object behaviors.

When a new class implements IBehavior or IClassBehavior or extends TBehavior or TClassBehavior, it may be attached to an object by calling the object's attachBehavior. The behaviors associated name can then be used to enableBehavior or disableBehavior the specific behavior.

All behaviors may be turned on and off via enableBehaviors and disableBehaviors, respectively. To check if behaviors are on or off a call to getBehaviorsEnabled will provide the variable.

Attaching and detaching whole sets of behaviors is done using attachBehaviors and detachBehaviors. clearBehaviors removes all of an object's behaviors.

asa returns a behavior of a specific name. isa is the behavior inclusive function that acts as the PHP operator instanceof. A behavior could provide the functionality of a specific class thus causing the host object to act similarly to a completely different class. A behavior would then implement IInstanceCheck to provide the identity of the different class.

Class behaviors are similar to object behaviors except that the class behavior is the implementation for all instances of the class. A class behavior will have the object upon which is being called be prepended to the parameter list. This way the object is known across the class behavior implementation.

Class behaviors are attached using attachClassBehavior and detached using detachClassBehavior. Class behaviors are important in that they will be applied to all new instances of a particular class. In this way class behaviors become default behaviors to a new instances of a class in __construct. Detaching a class behavior will remove the behavior from the default set of behaviors created for an object when the object is instanced.

Class behaviors are also added to all existing instances via the global fx event mechanism. When a new class behavior is added, the event fxAttachClassBehavior is raised and all existing instances that are listening to this global event (primarily after listen is called) will have this new behavior attached. A similar process is used when detaching class behaviors. Any objects listening to the global fx event fxDetachClassBehavior will have a class behavior removed.

Dynamic Intra-Object Events

Dynamic events start with dy. This mechanism is used to allow objects to communicate with their behaviors directly. The entire dy event space is valid. All attached, enabled behaviors that implement a dynamic event are called when the host object calls the dynamic event. If there is no implementation or behaviors, this returns null when no parameters are supplied and will return the first parameter when there is at least one parameter in the dynamic event.

null == $this->dyBehaviorEvent();
	5 == $this->dyBehaviorEvent(5); //when no behaviors implement this dynamic event

Dynamic events can be chained together within behaviors to allow for data filtering. Dynamic events are implemented within behaviors by defining the event as a method.

class TObjectBehavior extends TBehavior {
    public function dyBehaviorEvent($param1, $callchain) {
			//Do something, eg:  $param1 += 13;
			return $callchain->dyBehaviorEvent($param1);

This implementation of a behavior and dynamic event will flow through to the next behavior implementing the dynamic event. The first parameter is always return when it is supplied. Otherwise a dynamic event returns null.

In the case of a class behavior, the object is also prepended to the dynamic event.

class TObjectClassBehavior extends TClassBehavior {
    public function dyBehaviorEvent($hostobject, $param1, $callchain) {
			//Do something, eg:  $param1 += $hostobject->getNumber();
			return $callchain->dyBehaviorEvent($param1);

When calling a dynamic event, only the parameters are passed. The host object and the call chain are built into the framework.

Global Event and Dynamic event catching

Given that all global fx events and dynamic dy events are valid and operational, there is a mechanism for catching events called that are not implemented (similar to the built-in PHP method __call). When a dynamic or global event is called but a behavior does not implement it, yet desires to know when an undefined dynamic event is run, the behavior implements the interface IDynamicMethods and method __dycall.

In the case of dynamic events, __dycall is supplied with the method name and its parameters. When a global event is raised, via raiseEvent, the method is the event name and the parameters are supplied.

When implemented, this catch-all mechanism is called for event global event event when implemented outside of a behavior. Within a behavior, it will also be called when the object to which the behavior is attached calls any unimplemented dynamic event. This is the fall-back mechanism for informing a class and/or behavior of when an global and/or undefined dynamic event is executed.