RE: [eclipse-incubator-e4-dev] Declarative UI

[Kevin McGuire <Kevin_McGuire@xxxxxxxxxx>]

Hi folks,

I just got caught up on this great thread. 

Hallvard, good summary.

As another cut through the space, this
is what I'm hearing, two extremes, both compelling:

A) A "literal" model of the
UI. 
 
You know the target is SWT and the model
reflects exactly that.  If you know SWT, you can guess pretty easily
what to put in the angle brackets.  You get a serialization/deserialization
format.  For large UIs it can reduce your total Java code in-memory
footprint.  You can do things like build up the model in memory first,
then create the widget structure as a walk through the model.  You
can build that model from reading the current widget tree.  It allows
you to avoid widget reparenting issues by reading the widgets, destroying
them, then recreating them elsewhere (e.g in a second workbench window).
 It facilitates GUI builders.  Its a good basis from which to
build other model abstractions (see below).

B) An abstract model of UIs (say, functional).

Here you want to get "above"
the level of the widgets.  The domain of discorse is maybe one of
data display and user interaction, or common UI solution patterns, not
widgets and layouts.  This might be a model of UI requirements and
capabilities that get translated into concrete widgets. For example, "I
need a table, the user will add and remove from the table" generates
a table widget with add/remove buttons.  This can be handy if you
are generating a lot of UI panels for say pages of entry fields, dialogs,
and wizards.  It also provides a natural way to bridge to different
widget sets (e.g. gen to SWT, gen to web).  You likely forgo some
ability to tweak the UI but gain in speed of authoring, easier refactoring,
etc.  You also get free consistency in your UI since functionally
equivalent UI areas get gen'd the same.  Such models are much more
contentious though since you must convince yourself you're modelling the
right thing, and that either the limitations of the model are acceptable
or there's some "escape to assembler" path.

These two aren't mutually exclusive.
 If you're doing (B), its probably handy having (A) so you can do
a model to model transformation as the path to instantiating the actual
widgets.

The practical me likes (A) since the
benefits are clear and you don't need to think too deeply about the model
(this is a feature).
The theoretical me likes (B) since I
really love the notion of elevating the task of programming beyond the
mostly administrative task of 3GL programming.

I need to learn more, but it sounds
like XSWT is close to (A) although you might not get everything currently
like the live model.
Again I need to learn more, but is XAML
much more than (A)?  It seems less than (B) since I'm still talking
about a literal UI with a certain layout, labels, etc., although perhaps
in a more general manner.

Regards,
Kevin

"Yves YANG" <yves.yang@xxxxxxxxxxx>
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11/09/2008 11:16 AM

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Subject	RE: [eclipse-incubator-e4-dev] Declarative UI

Hi Hallvard,

Regarding the comparison between XAML and XSWT, I agree with you. 

As for the goals, I think the goal (1) is a wrong goal for XML since there
are other formats are more compact like JSON, or binary directly. The goal
(2) is necessary as declarative UI language. The goal (3) is rather than
a
model in memory. I vote (2) + (3). 

yves
-----Original Message-----
From: eclipse-incubator-e4-dev-bounces@xxxxxxxxxxx
[mailto:eclipse-incubator-e4-dev-bounces@xxxxxxxxxxx] On Behalf Of Hallvard
Trætteberg
Sent: Sunday, November 09, 2008 4:54 PM
To: E4 developer list
Subject: Re: [eclipse-incubator-e4-dev] Declarative UI

Kevin,

Kevin McGuire wrote:

> Shall I try to pick a time in say about two weeks?

OK for me. It has been mentioned that some will meet at ESE. I'm going
there

myself, but haven't yet received a confirmation about the e4 symposium.
I
was a 
day late with the position paper (didn't post here but to the email address
found in the call), but still I hope to be allowed to attend.

> Specifically, while it would be good to have presentations on XSWT,
XUL,
etc.
 > I think the agenda has to be more around approaches and goals.

In the last postings (Yves Yang and David Orme), there has been some
comparison 
of XML notations (XAML and XSWT). As pointed out by Yang, XSWT is perhaps
more 
targeted at serializing SWT. Or rather, it is a description of how to 
(procedurally) _build_ a specific SWT UI, while a XAML is a (declarative)
model 
of the (initial) _state_ of a UI. David and Yves, do you agree? Whether
or
not 
this difference is important, depends on the goal.

If the goal (1) is a compact notation from which to render an SWT UI, I
think 
XSWT's approach (guessing the meaning of names, based on type information
acquired by means of reflection) is best. If the goal (2) is a model for
describing the state of the UI, a model which lends itself to generation,
transformation and other processing, something XAML-like may be best. A
third 
(level) goal (3) is having a "live" model which is kept in sync
with the
running 
UI. Such a model can provide a more uniform, API-independent way of
manipulating 
  and listening to the UI.

These are different goals I can identify, and that I hope is a constructive
contribution to this discussion.

Personally, I favor goal (3), a model supporting live syncing with the
real
UI. 
If we design this model using EMF, we get scripting and databinding for
free
(it 
already exists). I think we can still use XSWT, XAML and other XML languages
as 
concrete syntaxes, since they may be more usable than EMF's native one.
The
XSWT 
processor can we thought of as a compiler that generates the EMF model
as 
intermediate code, instead of building the SWT UI directly. It should also
be 
possible to generate Java code from the EMF model, or perhaps compile it
directly to bytecode, for use in mobile applications.

Hallvard
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