[Laszlo-dev] About implicit attribute handlers

[Rami Ojares]

Also would be great if one could define more than reference in handler tag

Like this

<handler name="eventName" reference="eventSender1, eventSender2, 
eventSender3" args="eventArg">
     ...
</handler>

Or is this already possible?

- rami

10.2.2010 21:47, Rami Ojares kirjoitti:
> Hi,
>
> Here is a piece of typical OL xml
>
> <SomeClass height="${this.program.duration * x + y}">
> <attribute name="program"/>
> </SomeClas>
>
> This creates automatically a handler something along these lines
>
> <handler name="onduration" reference="this.program" args="newDuration">
>     this.setAttribute("height", this.program.duration * x + y);
> </handler>
>
> In my app it is very common that not only the duration of the program 
> changes but also the program
> attribute of SomeClass changes too.
>
> That's when things go wrong.
>
> I have ended up writing my own handlers in many places to alleviate 
> this issue.
>
> So my question is have others suffered from this also?
>
> Sometimes this issue arises also if the program is initialized so late 
> that the reference evaluates to null or undefined when the handler is 
> instantiated. And then the constraint does not work at all.
>
> Here is an exmaple that shows you what I mean.
> (I tried to make it as short as possible to demonstrate the issue)
>
> <canvas debug="true">
>
> <node name="dataNode1">
> <attribute name="data" type="string" value="AAA"/>
> </node>
>
> <node name="dataNode2">
> <attribute name="data" type="string" value="111"/>
> </node>
>
> <view name="dataConsumer" width="100" height="100" bgcolor="dodgerblue">
>
> <attribute name="dataSrc" value="${canvas.dataNode1}"/>
> <!-- If you don't provide initial value you will not get text at all 
> no matter how much you push the button -->
> <!-- <attribute name="dataSrc"/> -->
>
> <text text="${'[' + parent.dataSrc.data + ']'}"/>
> </view>
>
> <!-- This button tries to set a new value to dataConsumer but fails -->
> <button text="Push" y="100">
> <handler name="onclick">
>             dataConsumer.setAttribute("dataSrc", canvas.dataNode2);
> </handler>
> </button>
> </canvas>
>
> So here is my suggestion:
> when writing a constraint like
> - obj1.obj2.attr1
> - this.obj1.obj2.attr1
> - classroot.obj1.obj2.attr1
>
> Then the following code would be autogenerated
>
> - code for the method that "handles" the constraint logic (already 
> done in the current version)
> - Delegate that calls that method (already done in the current version)
> - delegate would be registered to listen onattr1 event from obj2 
> (already done in the current version)
> - delegate would be registered to listen onobj2 event from obj1 (new)
> - delegate would be registered to listen onobj1 event from this (first 
> 2 cases) or classroot (new)
>
> I don't know what the performance considerations for this would be but 
> I remember reading somewhere that delegates that do nothing have a 
> negligible performance impact.
> This would make the constraint system behave more as expected because 
> then it would truly follow the value you have declaratively commanded 
> that it should follow.
>
> What do you think?
>
> - rami
>