RE: [flexcoders] Extending MXML components (change from 1.5 to 2)

Thu, 23 Mar 2006 06:51:25 -0800

Tony,

 

Yes, we absolutely intend to continue supporting extending MXML with MXML, with the constraint that only one set of children be specified anywhere in the chain of derived components or the component instantiation.

 

What you’re seeing is a bug in beta 2 – the framework incorrectly raises the “multiple sets of children in base and derived components” error in cases where the superclass (A.mxml in your example) in fact has no children.

 

This will be fixed for beta 3; the workaround in beta 2 is to insert the following <Script/> code into the superclass, e.g. A.mxml:

 

<mx:Script>

/**

 *  This namespace is used for undocumented APIs -- usually implementation

 *  details -- which can't be private because they need to visible

 *  to other classes.

 *  APIs in this namespace are completely unsupported and are likely to

 *  change in future versions of Flex.

 */

namespace mx_internal = "http://www.adobe.com/2006/flex/mx/internal";

 

override mx_internal function setDocumentDescriptor(desc:mx.core.UIComponentDescriptor):void

{

       if (mx_internal::_documentDescriptor && mx_internal::_documentDescriptor.properties.childDescriptors)

       {

              if (desc.properties.childDescriptors)

              {

                     throw new Error("Multiple sets of visual children have been specified for this component (base component definition and derived component definition).");

              }

       }

       else

       {

              mx_internal::_documentDescriptor = desc;

              mx_internal::_documentDescriptor.document = this;

       }

}

</mx:Script>

 

Basil

 

From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Tony Pujals
Sent: Wednesday, March 22, 2006 6:02 PM
To: [email protected]
Subject: [flexcoders] Extending MXML components (change from 1.5 to 2)

 

In Flex 1.5, you could create an MXML component and then extend it with another custom component. For example, this would work:

 

A.mxml

<?xml version="1.0" encoding="utf-8"?>

<mx:Canvas xmlns:mx="http://www.adobe.com/2006/mxml">

</mx:Canvas>

 

 

B.mxml

<A xmlns:mx="http://www.adobe.com/2006/mxml">

                <mx:Button label="Hello" click="mx.controls.Alert.show('Hello')" />

</A>

 

 

Test.mxml

<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">

                <B />

</mx:Application>

 

 

 

 

How was this useful? Well, for example, for an HTML page editor, we had an Element.mxml component subclassed by ImageElement.mxml and TextElement.mxml.

 

This does not work with any of the Flex 2 alpha/betas. Flash 8.5 displays this diagnostic:

 

Error: Multiple sets of visual children have been specified for this component (base component definition and derived component definition)

                at mx.core::Container/http://www.adobe.com/2006/flex/mx/internal::setDocumentDescriptor()

                at A/initialize()

                at B/initialize()

                at mx.core::UIComponent/http://www.adobe.com/2006/flex/mx/internal::rawChildAdded()

                at mx.core::UIComponent/addChildAt()

                at mx.core::Container/addChild()

                at mx.core::Container/createComponentFromDescriptor()

                at mx.core::Container/createComponentsFromDescriptors()

                at mx.core::Application/createComponentsFromDescriptors()

                at mx.core::Container/mx.core:Container::createChildren()

                at mx.core::UIComponent/initialize()

                at mx.core::Container/initialize()

                at mx.core::Application/initialize()

                at flextest/initialize()

                at mx.managers::SystemManager/::initializeChild()

                at mx.managers::SystemManager/::initializeTopLevelWindow()

                at mx.managers::SystemManager/::frameEndHandler()

 

 

 

It’s not that the error message isn’t clear, per se, but since this is different behavior, I’m curious …. Can you only extend mx components but not you’re own, or this only possible with ActionScript components and not mxml….?

 

Thanks,

 

Tony

 

 

tony pujals| senior engineer | Yahoo! SiteBuilder Express

p. 408.349.6284 | e. tonyp * yahoo-inc * com | y!id tonypujals

 

 

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