Adobe® Flex® 4 Language Reference
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mx.core 
ComponentDescriptor 
Packagemx.core
Classpublic class ComponentDescriptor
InheritanceComponentDescriptor Inheritance Object
Subclasses UIComponentDescriptor

Language Version: ActionScript 3.0
Product Version: Flex 3
Runtime Versions: Flash Player 9, AIR 1.1

ComponentDescriptor is the base class for the UIComponentDescriptor class, which encapsulates the information that you specified in an MXML tag for an instance of a visual component. In Flex, non-visual components are treated differently and do not have descriptors, but in a future version the ComponentDescriptor base class may be used for them as well.

Most of the tags in an MXML file describe a tree of UIComponent objects. For example, the <mx:Application> tag represents a UIComponent object, and its child containers and controls are all UIComponent objects.

The MXML compiler compiles each of these MXML tags into a UIComponentDescriptor instance. To be precise, the MXML compiler autogenerates an ActionScript data structure which is a tree of UIComponentDescriptor objects.

At runtime, the createComponentsFromDescriptors() method of the Container class uses the information in the UIComponentDescriptor objects in the container's childDescriptors array to create the actual UIComponent objects that are the container's children, plus deeper descendants as well. Depending on the value of the container's creationPolicy, property, the descendants might be created at application startup, when some part of the component is about to become visible, or when the application developer manually calls the createComponentsFromDescriptors() method.

You do not typically create ComponentDescriptor or UIComponentDescriptor instances yourself; you can access the ones that the MXML compiler autogenerates, via the childDescriptors array of the Container class.

See also



Public Properties
 PropertyDefined By
 Inheritedconstructor : Object
A reference to the class object or constructor function for a given object instance.
Object
  document : Object
A reference to the document Object in which the component is to be created.
ComponentDescriptor
  events : Object
An Object containing name/value pairs for the component's event handlers, as specified in MXML.
ComponentDescriptor
  id : String
The identifier for the component, as specified in MXML.
ComponentDescriptor
  properties : Object
[read-only] An Object containing name/value pairs for the component's properties, as specified in MXML.
ComponentDescriptor
  propertiesFactory : Function
A Function that returns an Object containing name/value pairs for the component's properties, as specified in MXML.
ComponentDescriptor
 Inheritedprototype : Object
[static] A reference to the prototype object of a class or function object.
Object
  type : Class
The Class of the component, as specified in MXML.
ComponentDescriptor
Public Methods
 MethodDefined By
  
ComponentDescriptor(descriptorProperties:Object)
Constructor.
ComponentDescriptor
 Inherited
Indicates whether an object has a specified property defined.
Object
  
Invalidates the cached properties property.
ComponentDescriptor
 Inherited
Indicates whether an instance of the Object class is in the prototype chain of the object specified as the parameter.
Object
 Inherited
Indicates whether the specified property exists and is enumerable.
Object
 Inherited
Sets the availability of a dynamic property for loop operations.
Object
 Inherited
Returns the string representation of this object, formatted according to locale-specific conventions.
Object
  
Returns the string "ComponentDescriptor_" plus the value of the id property.
ComponentDescriptor
 Inherited
Returns the primitive value of the specified object.
Object
Property Detail

document

property
public var document:Object

Language Version: ActionScript 3.0
Product Version: Flex 3
Runtime Versions: Flash Player 9, AIR 1.1

A reference to the document Object in which the component is to be created.

See also

events

property 
public var events:Object

Language Version: ActionScript 3.0
Product Version: Flex 3
Runtime Versions: Flash Player 9, AIR 1.1

An Object containing name/value pairs for the component's event handlers, as specified in MXML.

For example, if you write

      <mx:DataGrid id="dg" initialize="fetchData(); initDataGrid();"  change="changeHandler(event);"/>
      

then the descriptor's events property is the Object

      { initialize: "__dg_initialize", change: "__dg_change" }
      

The eventproperty is null if no MXML event handlers were specified for the component

The strings "__dg_initialize" and "__dg_change" are the names of event handler methods that the MXML compiler autogenerates. The body of these methods contain the ActionScript statements that you specified as the values of the event attributes. For example, the autogenerated initialize handler is

      public function __dg_initialize(event:mx.events.FlexEvent):void
      {
          fetchData();
          initDataGrid();
      }
      

You should not assume that the autogenerated event handlers will always be specified by name; this may change in a future version of Flex.

This property is used by the Container method createComponentsFromDescriptors() to register the autogenerated event handlers using the addEventListener() method.

id

property 
public var id:String

Language Version: ActionScript 3.0
Product Version: Flex 3
Runtime Versions: Flash Player 9, AIR 1.1

The identifier for the component, as specified in MXML.

For example, if you write

      <mx:TextInput id="firstName" text="Enter your first name here"/>
      

then the descriptor's id property is the String "firstName".

The id property is null if no MXML id was specified for the component.

The value of the id property becomes the name of a public variable in the MXML document object, autogenerated by the MXML compiler. The value of this variable is a reference to the UIComponent object created from this descriptor. This is why you can, for example, reference the TextInput control's text property as firstName.text from anywhere within the document containing this TextInput instance.

If an id is specified, and it isn't the empty string, it also becomes the name of the DisplayObject object. If an id is not specified or is empty, the DisplayObject object's name remains an autogenerated string, such as "Button3", as returned by the NameUtil.createUniqueName() method. The name is used in generating the string returned by the toString() method. It can also be used to find the component from its parent by calling getChildByName().

See also

properties

property 
properties:Object  [read-only]

Language Version: ActionScript 3.0
Product Version: Flex 3
Runtime Versions: Flash Player 9, AIR 1.1

An Object containing name/value pairs for the component's properties, as specified in MXML.

For example, if you write

      <mx:TextInput width="150" text="Hello"/>
      

then the descriptor's properties property is the Object

      { width: 150, text: "Hello" }
      

The properties property is null if no MXML properties were specified for the component. In this case, the component will use default property values.

This Object is produced by calling the function specified by the propertiesFactory property, and then cached for subsequent access. However, when a Repeater produces multiple instances of a component from the same descriptor, a fresh copy of the properties Object should be produced for each component instance so that they don't share property values which are Arrays or Object references. The Repeater accomplishes this by calling the invalidateProperties() method on the descriptor.



Implementation
    public function get properties():Object

See also

propertiesFactory

property 
public var propertiesFactory:Function

Language Version: ActionScript 3.0
Product Version: Flex 3
Runtime Versions: Flash Player 9, AIR 1.1

A Function that returns an Object containing name/value pairs for the component's properties, as specified in MXML.

For example, if you write

      <mx:TextInput width="150" text="Hello">
      

then the descriptor's propertiesFactory property is the Function:

      function():Object { return { width: 150, text: "Hello" }; }
      

The propertiesFactoryproperty is null if no MXML properties were specified for the component. In this case, the component will use default property values.

The reason that propertyFactory is a Function returning an Object rather than an actual Object is to allow the tree of ComponentDescriptor objects to "unfold" incrementally. If all the descriptors in the descriptor tree for the document were created at launch time, the time to launch would be greater.

The properties property returns a cached Object that was produced by this factory function.

Note: Event handlers such as click="doSomething();" appear in the events Object, not in the properties Object.

See also

type

property 
public var type:Class

Language Version: ActionScript 3.0
Product Version: Flex 3
Runtime Versions: Flash Player 9, AIR 1.1

The Class of the component, as specified in MXML.

For example, if you write

      <mx:TextInput/>
      

then the descriptor's type property the Class mx.controls.TextInput.

The property is never null for the ComponentDescriptor objects created by the MXML compiler, because every MXML tag has a tag name such as mx:TextInput.

The mapping between an MXML tag and its corresponding class is determined by the XML namespace and the "manifest" file, if any, that is associated with that namespace. For example, the standard Flex namespace http://www.adobe.com/2006/mxml represented by the mx: prefix is associated (in the flex-config.xml file) with the manifest file mxml-manifest.xml, and this file has the tag

      <component id="TextInput" class="mx.controls.TextInput"/>
      

which maps the tag name mx:TextInput to the Class mx.controls.TextInput. Note that the use of a manifest file allows components in single XML namespace to map to classes in multiple ActionScript packages.

Constructor Detail

ComponentDescriptor

()Constructor
public function ComponentDescriptor(descriptorProperties:Object)

Language Version: ActionScript 3.0
Product Version: Flex 3
Runtime Versions: Flash Player 9, AIR 1.1

Constructor.

Parameters
descriptorProperties:Object — An Object containing name/value pairs for the properties of the ComponentDescriptor object, such as its type, id, propertiesFactory and events.
Method Detail

invalidateProperties

()method
public function invalidateProperties():void

Language Version: ActionScript 3.0
Product Version: Flex 3
Runtime Versions: Flash Player 9, AIR 1.1

Invalidates the cached properties property. The next time you read the properties property, the properties are regenerated from the function specified by the value of the propertiesFactory property.

toString

()method 
public function toString():String

Language Version: ActionScript 3.0
Product Version: Flex 3
Runtime Versions: Flash Player 9, AIR 1.1

Returns the string "ComponentDescriptor_" plus the value of the id property.

Returns
String — The string "ComponentDescriptor_" plus the value of the id property.