Oct 7, 2006

PRADO Component

A component is an instance of TComponent or its child class. The base class TComponent implements the mechanism of component properties and events.

Component Properties PRADO

A component property can be viewed as a public variable describing a specific aspect of the component, such as the background color, the font size, etc. A property is defined by the existence of a getter and/or a setter method in the component class. For example, in TControl, we define its ID property using the following getter and setter methods,

class TControl extends TComponent {  
public function getID()
{
...
}

public function setID($value)
{
...
}
}

To get or set the ID property, do as follows, just like working with a variable,

$id = $component->ID; $component->ID = $id;
This is equivalent to the following,
$id = $component->getID(); $component->setID( $id );

A property is read-only if it has a getter method but no setter method. Since PHP method names are case-insensitive, property names are also case-insensitive. A component class inherits all its ancestor classes' properties.

Subproperties

A subproperty is a property of some object-typed property. For example, TWebControl has a Font property which is of TFont type. Then the Name property of Font is referred to as a subproperty (with respect to TWebControl).

To get or set the Name subproperty, use the following method,

$name = $component->getSubProperty('Font.Name'); $component->setSubProperty('Font.Name', $name);
This is equivalent to the following,
$name = $component->getFont()->getName();
$component->getFont()->setName( $name );

Component Events

Component events are special properties that take method names as their values. Attaching (setting) a method to an event will hook up the method to the places at which the event is raised. Therefore, the behavior of a component can be modified in a way that may not be foreseen during the development of the component.

A component event is defined by the existence of a method whose name starts with the word on. The event name is the method name and is thus case-insensitve. For example, in TButton, we have

class TButton extends TWebControl {  
public function onClick( $param ) {
...
}
}
This defines an event named OnClick, and a handler can be attached to the event using one of the following ways,
$button->OnClick = $callback;
$button->OnClick->add( $callback );
$button->OnClick[] = $callback;
$button->attachEventHandler( 'OnClick' , $callback );
where $callback refers to a valid PHP callback (e.g. a function name, a class method array($object,'method'), etc.)

Namespaces

A namespace refers to a logical grouping of some class names so that they can be differentiated from other class names even if their names are the same. Since PHP does not support namespace intrinsically, you cannot create instances of two classes who have the same name but with different definitions. To differentiate from user defined classes, all PRADO classes are prefixed with a letter 'T' (meaning 'Type'). Users are advised not to name their classes like this. Instead, they may prefix their class names with any other letter(s).

A namespace in PRADO is considered as a directory containing one or several class files. A class may be specified without ambiguity using such a namespace followed by the class name. Each namespace in PRADO is specified in the following format,

PathAlias.Dir1.Dir2
where PathAlias is an alias of some directory, while Dir1 and Dir2 are subdirectories under that directory. A class named MyClass defined under Dir2 may now be fully qualified as PathAlias.Dir1.Dir2.MyClass.

To use a namespace in code, do as follows,

Prado::using('PathAlias.Dir1.Dir2.*');
which appends the directory referred to by PathAlias.Dir1.Dir2 into PHP include path so that classes defined under that directory may be instantiated without the namespace prefix. You may also include an individual class definition by
Prado::using('PathAlias.Dir1.Dir2.MyClass');
which will include the class file if MyClass is not defined.

Component Instantiation

Component instantiation means creating instances of component classes. There are two types of component instantation: static instantiation and dynamic instantiation. The created components are called static components and dynamic components, respectively.

Dynamic Component Instantiation

Dynamic component instantiation means creating component instances in PHP code. It is the same as the commonly referred object creation in PHP. A component can be dynamically created using one of the following two methods in PHP,

$component = new ComponentClassName; $component = Prado::createComponent('ComponentType');
where ComponentType refers to a class name or a type name in namespace format (e.g. System.Web.UI.TControl). The second approach is introduced to compensate for the lack of namespace support in PHP.

Static Component Instantiation

Static component instantiation is about creating components via configurations. The actual creation work is done by the PRADO framework. For example, in an application configuration, one can configure a module to be loaded when the application runs. The module is thus a static component created by the framework. Static component instantiation is more commonly used in templates. Every component tag in a template specifies a component that will be automatically created by the framework when the template is loaded. For example, in a page template, the following tag will lead to the creation of a TButton component on the page,

<com:TButton Text="Register" />

No comments:

Post a Comment

Newer Post Older Post Home