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

[James Robey]

Its quite clear using the sendEvent method, like you illustrate, and  
although i like One Way to Do things, it reads right! So on that score  
carry on. On another angle, what if i get a name from a server source  
and the name is the same, but other values are different, and because  
of that other operations don't occur? I think it's a iffy move. If you  
do change it, it's certainly not the end of the world.

.j

On Apr 25, 2009, at 7:21 PM, Henry Minsky wrote:

>
> It seems to me that in your example, you really want to send an  
> event, and setting the attribute is one step removed from that. So  
> maybe the most
> clear way to implement that would be to call sendEvent directly
>
>
> <method name="update">
>    canvas.onupdate.sendEvent( true);
> </method>
>
>
>
>
> On Sat, Apr 25, 2009 at 6:46 PM, jamesr <circlecycle at gmail.com> wrote:
>
>
> On Fri, Apr 17, 2009 at 6:36 PM, P T Withington <ptw at pobox.com> wrote:
> I'm working on http://jira.openlaszlo.org/jira/browse/LPP-8058 to  
> reduce the number of extraneous events sent by implementing the  
> following optimization:
>
> If an attribute is constrained, and the values the constraint  
> depends on change, but the result of the constraint does _not_  
> change, then the attribute will not be updated (to the identical  
> value) and, more importantly, no `on` event will be sent.  The  
> change can be demonstrated by considering the following:
>
> <canvas layout="axis: x; spacing: 5" debug="true">
>    <attribute name="jay" value="2" />
>    <handler name="onjay">Debug.info("onjay")</handler>
>    <attribute name="kay" value="4" />
>    <handler name="onkay">Debug.info("onkay")</handler>
>    <attribute name="jaykay" value="${jay*kay}" />
>    <handler name="onjaykay">
>       Debug.info("onjaykay: %d * %d = %d", jay, kay, jaykay);
>    </handler>
>    <button onclick="canvas.setAttribute('jay', canvas.jay)">Same</ 
> button>
>    <button onclick="canvas.setAttribute('jay', canvas.jay +  
> 1)">Different</button>
> </canvas>
>
> In the current system, setting `jay` will _always_ cause `jaykay` to  
> be updated, and for there to be an `onjaykay` event.  In the  
> proposed change, setting `jay` to the same value, will cause an  
> `onjay` event, but the constraint on `jaykay` will have the same  
> result, so `jaykay` will _not_ be updated and there will be _no_  
> `onjaykay` event sent.
>
> Comments?  Questions?
>
> 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>
>
> where i expect the update handlers to get run on true regardless of  
> whether they were already true before. This change would require  
> that i set update to false after such an event. In my own runtime, i  
> include a "touch" method which allows me to fire an event without  
> having to set an explicit value, just for these type of delegate  
> networks. I would toss in my two cents by saying that it would be  
> nice to have one or the other available to me.
>
> there might be other methods to accomplish the same thing - i'm just  
> pointing out a pattern that my code depends on, currently
>
> -james
>
>
>
> -- 
> Henry Minsky
> Software Architect
> hminsky at laszlosystems.com
>
>

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