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Component is the base class that implements the property, event and behavior features.
Component provides the event and behavior features, in addition to the property feature which is implemented in its parent class Object.
Event is a way to "inject" custom code into existing code at certain places. For example, a comment object can trigger an "add" event when the user adds a comment. We can write custom code and attach it to this event so that when the event is triggered (i.e. comment will be added), our custom code will be executed.
An event is identified by a name that should be unique within the class it is defined at. Event names are case-sensitive.
One or multiple PHP callbacks, called event handlers, can be attached to an event. You can call trigger() to raise an event. When an event is raised, the event handlers will be invoked automatically in the order they were attached.
To attach an event handler to an event, call on():
$post->on('update', function($event) {
// send email notification
});
In the above, an anonymous function is attached to the "update" event of the post. You may attach the following types of event handlers:
- anonymous function:
function($event) { ... } - object method:
[$object, 'handleAdd'] - static class method:
['Page', 'handleAdd'] - global function:
'handleAdd'
The signature of an event handler should be like the following:
function foo($event)
where $event is an Event object which includes parameters associated with the event.
You can also attach a handler to an event when configuring a component with a configuration array. The syntax is like the following:
[
'on add' => function($event) { ... }
]
where on add stands for attaching an event to the add event.
Sometimes, you may want to associate extra data with an event handler when you attach it to an event and then access it when the handler is invoked. You may do so by
$post->on('update', function($event) {
// the data can be accessed via $event->data
}, $data);
A behavior is an instance of Behavior or its child class. A component can be attached with one or multiple behaviors. When a behavior is attached to a component, its public properties and methods can be accessed via the component directly, as if the component owns those properties and methods.
To attach a behavior to a component, declare it in behaviors(), or explicitly call attachBehavior. Behaviors declared in behaviors() are automatically attached to the corresponding component.
One can also attach a behavior to a component when configuring it with a configuration array. The syntax is like the following:
[
'as tree' => [
'class' => 'Tree',
],
]
where as tree stands for attaching a behavior named tree, and the array will be passed to \Yii::createObject()
to create the behavior object.