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layout: docpage title: Metadata description: Decorate classes, properties and methods with extra information that can be used at compile or run time permalink: /features/as3/metadata

Metadata

Decorate classes, properties and methods with extra information that can be used at compile or run time

Metadata decorate classes, properties and methods to give extra data to the compiler that can be used to generate code at compile time that depends on that metadata values, or can be used at runtime for code that can interpret that data to perform some specific functionality. With Apache Royale, you can use meta in both AS3 and MXML.

An example in AS3 of a Bindable Metadata declaration decorating a variable is the following:

[Bindable]
public var someVariable:Boolean = true;

In *MXML an example of an Event Metadata declared for that MXML file will be the following. Notice that you need to add to the special fx:Metadata tag:

<fx:Metadata>
	[Event(name="someEvent", type="org.apache.royale.events.Event")]
</fx:Metadata>

Available Metadata

Here you can find the list of all possible Royale Metadata available:

Bindable

Event

DefaultProperty

The default property used when additional MXML content appears within an element's definition in an MXML file.

For example, Jewel Group defines [DefaultProperty("mxmlContent")] in its class code. When using this component, instead of writting:

<j:Group>
    <j:mxmlContent>
        <j:Button/>
    </j:mxmlContent>
</j:Group>

we can simplify declarations by removing mxmlContent tags saving several lines of code:

<j:Group>
    <j:Button/>
</j:Group>

RemoteObject

Managed

ChangeEvent

NonCommittingChangeEvent

Transient

SWFOverride

Inspectable

PercentProxy

Example of use

For example, you may create an MXML component that defines a new event. To make that event known to the Royale compiler that you can reference it in MXML, you insert the [Event] metadata tag into your component, as the following example shows:

<fx:Metadata>
	[Event(name="someEvent")]
</fx:Metadata>

In this example, you use metadata to make the someEvent event available to the MXML compiler.

In an MXML file, you insert the metadata tags either in an fx:Script block along with your ActionScript code, or in an fx:Metadata block, as the following example shows:

<j:Group xmlns:fx="http://ns.adobe.com/mxml/2009"
	xmlns:j="library://ns.apache.org/royale/jewel">

    <fx:Metadata>
        [Event("enableChange")]
    </fx:Metadata>

    <fx:Script>
    <![CDATA[
        private var _enable:Boolean;

        // Add the [Inspectable] metadata tag before the individual property.
        [Inspectable(defaultValue="false")]
        public function set enable(val:Boolean):void {
            _enable = val;
            this.enabled = val;

            // Define event object, initialize it, then dispatch it. 
            var eventObj:Event = new Event("enableChange");
            dispatchEvent(eventObj);
        }
    ]]>
    </fx:Script>
</j:Group>

When using metadata tags in ActionScript class files, you insert the metadata tag directly into the class definition; you do not use the fx:Metadata tag. In AS3 you can use metadata as well in methods and properties of the class.

Custom Metadata

You can create your own custom metadata. This info will come soon...