[Laszlo-user] Proposal to change how constraints are propagated

[P T Withington]

On 2009-04-25, at 18:46EDT, jamesr wrote:

> I use handlers to fire functionality without actually changing any  
> values.
> An example would be
>
> <canvas>
>    <attribute name="update" type="boolean" value="false"/>
>    <...>
>       <handler name="onupdate" reference="canvas">
>           //do something
>       </handler>
>    </...>
> <canvas>
>
> <method name="update">
>   canvas.setAttribute('update', true);
> </method>

I think a more straightforward way to do this would be:

<canvas>
    <event name="onupdate" />
    <...>
       <handler name="onupdate" reference="canvas">
           //do something
       </handler>
    </...>
<canvas>

<method name="update">
   canvas.onupdate.sendEvent(true);
</method>

You don't actually have to name your event 'on'something, that is just  
the convention for events that get automatically created for  
attributes.  But you can also have straight-up events that are just  
used to hang handlers off of (that will all get run when the event is  
sent).  You get to send one value along with the event, which your  
handler will receive, if it specifies and argument.

See also:  http://jira.openlaszlo.org/jira/browse/LPP-6034