How to make reusable widgets?

[ailinykh]

Hello, everybody!
I'm confused with latest MVP pattern. My problem is:
Let's say I have main layout which consists of several widgets.
Something like this

<g:DockLayoutPanel unit='EM'>
<g:north size="4">
<my:MyNorthWidget/>

</g:north>
<g:west size="20">
<my:MyWestWidget/>

</g:west>
<g:center>
<my:MyCenterWidget/>
</g:center>
</g:DockLayoutPanel>

So, I have three widgets- MyNorthWidget, MyWestWidget and
MyCenterWidget. I would like to have a presenter (Activity) for each
of them.
But I have only one Place, which means I may have only one Activity
and this Activity is aware about all widgets. Is there a way to make
widgets reusable?
Thank you,
Andrey

[Thomas Broyer]

Place <-> Activity is *not* a 1:1.

Its' hard to tell from your example how it'd better be done, so I'll
try to guess.

Case 1: you don't really have those widgets, but rather "placeholders"
where you'll put them on place change (what I call "display regions").
In other words, this is the layout of your app, at the "top level" of
your widget hierarchy
In this case, you'll have 3 ActivityManager, one for each display
region, and each one with its ActivityMapper.

Case 2: the DockLayoutPanel is the "view" of an activity, and you want
to subdivide it into 3 "subactivities". In this case, your
"docklayoutpanel activity" should probably instantiate and manage the
lifecycle of the subactivities itself; or maybe you shouldn't even use
the Activity interface for your "sub parts". The idea anyway is that
your "docklayoutpanel activity" *knows* the "sub parts" and manages
them, whether they're "just widgets" (or components composed of a
presenter and a view).

Maybe this can help you: http://tbroyer.posterous.com/gwt-21-activities-nesting-yagni
(it was written for 2.1 M3 and I haven't updated it yet, you'll find
the list of changes between M3 and RC1 at
http://tbroyer.posterous.com/gwt-21-places-activities-what-changed-between
)