Re: [gef-dev] 2.2 suggestion: Draw2D LayoutManagers as decorators

[Randy Hudson <hudsonr@xxxxxxxxxx>]

Could you try explaining the overall
problem you are trying to solve first and then propose a solution? What
did you mean by "layouts ... that have associated layouts"?  Are
you talking about constraints?

I don't think you have run into a limitation
of the layout mechanism, maybe just the provided layout managers. The layout
mechanism is very capable, just look at IBM's PageDesigner which renders
HTML, or the TreeExample in the draw2d.examples project.  Is there
any reason why you can't write your own chained or compound layoutmanager
within the current API?

-randy

Richard Clark <rdclark@xxxxxxxxxxxxxxxx> Sent by: gef-dev-admin@xxxxxxxxxxx 05/01/2003 12:57 PM Please respond to gef-dev

To:        <gef-dev@xxxxxxxxxxx>         cc:                 Subject:        [gef-dev] 2.2 suggestion: Draw2D LayoutManagers as decorators

As I've worked on several editors, I've run into limitations
in the Draw2D layout and LayoutManager classes. In particular, there are
times I'd like to restrict a layout to a specific area of the screen (a
la XYLayout), but let the individual components arrange themselves (a la
DelegatingLayout.) 

Some layouts stand alone, while others have associated layout managers
(and only work with those managers). This can make it difficult to choose
an appropriate layout or to use the layout manager of one's choice. So
I'd like to suggest a refactoring of the Layout code to use "decorators":
1. Allow a Layout to have a chain of Layout Managers, ending in a default
"null" manager contained within AbstractLayout (replace setLayoutManager
with addLayoutManager / removeLayoutManager)
2. replace (or extend) setConstraint with boolean addConstraint(IFigure,
Object) & removeConstraint(IFigure, Object). These calls would be chained,
and could "consume" the constraint (by returning true) in which
case the chain ends. Unconsumed constraints could be caught by the null
layout manager and either be swallowed silently (returning false at the
top level) or raise an exception.

This would move us a long way toward having "toolkits" of layout
managers that could be composed together to get the desired effect (as
in the "arrange yourselves within this rectangle" example).

..Richard

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