[Laszlo-dev] What is a node? [Was For Review: Change 20070806-hqm-8 Summary: make base abstract LzDataProvider class]

[P T Withington]

To me, a node is an element in the DOM.  It has a parent and  
children.  Nodes get created by LZX tags.  They don't participate in  
layout (only view and their subclasses do), but you can navigate to  
them in the DOM.  To me, that is the primary purpose of node-ness:   
that you can navigate to/from the node in the DOM, you can ask for  
the node's parent, etc.

Constraining an attribute to an expression is a feature of the LZX  
language.  Since the only thing in LZX that can have attributes is a  
node, that nifty constraint language also requires node-ness.  But we  
could think about separating that out.  Henry has asked that we  
invent a Javascript syntax to write constraints as concisely as we do  
in LZX.

But, the elements of a constraint expression do not have to be a  
node.  See, for example, LzGlobalMouse.  You can constrain a view  
attribute to the mouse position, even though the mouse is not a node.

By the same token, the LZX language makes sending an event when you  
use setAttribute on an attribute automatic.  Again, in LZX you have  
to be a node to call setAttribute.  This would be another thing we  
could extend to Javascript if we wanted.

Again, you do not have to be a node to send events.  Again,  
LzGlobalMouse is an example of an existing object that is not a  
node.  You can request to be notified of mouse events even though the  
mouse object is not a node.

There are already Javascript classes that the LZX developer has to  
know about, so this is not a new concept, although admittedly, it is  
not the usual case.  The LZX developer already has to write  
Javascript to implement methods, initialize attributes, handle  
events, etc.  Javascript is a part of the LZX language.  It is not a  
secret.

If we want to improve the performance of LZX programs, we need to  
stop using a sledgehammer where a tack hammer will do.

On 2007-08-06, at 20:24 EDT, Pablo Kang wrote:

> I'm ok with writing script as long it's documented as such.
>
> I do think this would be a departure from current recommended LZX  
> coding practices. As I understand it (from Sarah and David), the  
> policy is to make everything as LZX friendly as possible.
>
> I'm assuming if datarequest and dataprovider don't extend from node  
> this also means that they can't be constrained to or don't  
> participate in the event system, right?
>
> pablo
>
> On Mon, 6 Aug 2007, P T Withington wrote:
>
>> Right.  That is the question I am asking.  Is the script tag not  
>> sufficient? This seems like a 'experts only' area, where the  
>> script tag should be fine, to me.  Given that nodes are heavy, I  
>> would avoid making things a node if I didn't have to.
>>
>> On 2007-08-06, at 19:48 EDT, Pablo Kang wrote:
>>
>>> This is so I can extend datarequest and dataprovider using LZX in  
>>> diamond. The other option is that I extend these classes using a  
>>> script tag.
>>> On Mon, 6 Aug 2007, P T Withington wrote:
>>>> Question:
>>>> Is there a reason to make dataprovider a node?  Does it need to  
>>>> show up in the DOM, or is it just a property of a dataset?  Do  
>>>> we really need to extend it in LZX, or is making it extensible  
>>>> only from script sufficient? It seems that the answer should be  
>>>> the same for dataprovider and datarequest.  I think is should be  
>>>> just a javascript class.
>>>> Otherwise approved.
>>>> On 2007-08-06, at 17:05 EDT, Henry Minsky wrote:
>>>>> Change 20070806-hqm-8 by hqm at IBM-2E06404CB67 on 2007-08-06  
>>>>> 17:02:34 EDT
>>>>>   in /cygdrive/c/users/hqm/openlaszlo/wafflecone
>>>>>   for http://svn.openlaszlo.org/openlaszlo/branches/wafflecone
>>>>> Summary: make base abstract LzDataProvider class
>>>>> New Features:
>>>>> This implements a common base class for LzDataProvider  
>>>>> implementations
>>>>> to inherit from
>>>>> Bugs Fixed:
>>>>> Technical Reviewer: ptw (pending)
>>>>> QA Reviewer: (pending)
>>>>> Doc Reviewer: (pending)
>>>>> Documentation:
>>>>> Release Notes:
>>>>> Details:
>>>>> Tests:
>>>>> Files:
>>>>> M      WEB-INF/lps/lfc/kernel/swf/LzHTTPLoader.as
>>>>> M      WEB-INF/lps/lfc/data/LzHTTPDataProvider.lzs
>>>>> A      WEB-INF/lps/lfc/data/LzDataProvider.lzs
>>>>> Changeset: http://svn.openlaszlo.org/openlaszlo/patches/ 
>>>>> 20070806-hqm-8.tar
>>>>> -- 
>>>>> Henry Minsky
>>>>> Software Architect
>>>>> hminsky at laszlosystems.com
>>