Don't think of our mediators as being part of a Model/View/Control
implementation. Think of them as how a MVC implementation gets access
to the 'M'.
Here is the intent of the mediator design pattern:
Define an object that encapsulates how a set of objects interact.
Mediator promotes loose coupling by keeping objects from
referring to each other explicitly, and it lets you vary their
interaction independently.
Design Patterns Elements of Reusable
Object-Oriented Software, Gamma, Erich et al, 1995, p 273.
It may look like overkill in our application which deals with only one
data format from tne source. However, I believe it's appropriate to
our goal of learning good practices as we build the app. We of could
chose to just mix things together more as described here.
http://en.wikipedia.org/wiki/Spaghetti_code
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Date: Fri, 15 Oct 2010 12:03:02 -0400
From: bwchaney@xxxxxxxx
To: tssg-tech@xxxxxxxxxxxxx
Subject: [tssg-tech] Re: Android mediators
Julie, I believe the articel you mention refers to a business or
person mediator, not the 'Mediator' pattern as defined in the book
'Design Patterns' by Gamma et. al. While the pattern derives its name
from the real-world analogy, it is a little more specific to software
design.
After consulting the Gamma book (which I have owned and meant to read
for a decade :-) it seems a 'Mediator' pattern's function is to
facilite two-way communication between components and centralizing
control. It is suited, for example, to propagating change among
dependent components, in our case, for example, coordinating different
views, like updating them when state changes (like inactivating
buttons, etc...) or if the user changes a preference that affects
multiple parts of the system (not necessarily when teh data changes!
see below)
Also, it appears that Android Adapters are not really Mediators, but
rather follow the 'Facade' or 'Adapter' (aptly named) patterns, which
also de-couple components, but facilitates communication between them
in one direction only.
Jim, I still would like to understand the need and role of a
'Mediator' component as part of an MVC architecture, which already
offers separation of concerns, if not necessarily loose coupling
(which may or may not always be desirable).
The following article describes MVC and also highlights the issue of
'is the Controller a Mediator?'
http://www.phpwact.org/pattern/model_view_controller
In the Android architecture, I see the Activity as the Controller,
the View as the View, and the data source as the Model (rss or
database in our case) The Android Adapter connects the View and the
Model, but the Controller picks which adapter to use! As a
clarification to an earlier post, there is no such thing as an Adapter
to an Activity. The Activity controls and creates the Adapter, but the
Adapter is a bridge between a View and a data source (Model).
Android Adapters, by the way, also handle asynchronous updating of
data! this could come in real handy. You can define listeners on an
Adapter for when the data changes, and it automatically updates theView.
Bea
Julie Carwellos wrote:
In trying to get a better "feel" for what Jim intended for the
Mediator, I looked around for other Android mediators. Here's one:
http://internet2go.net/news/ad-networks/networks-vs-mediators-one-sdk-rule-them-all
Ads come in in various formats for mobile apps because they're
from different suppliers, and this mediator makes life easier for
the Activity. A single call into the mediator gets reorganized to
present the ad in a way the Activity understands it and can send
it to the display.
Jim, is this what your intention was for the mediator - to make
RSS and Database look the same to the Activity? And maybe for
future suppliers of data for the view? e.g. Other Event feeds or
even APIs.
Thanks,
Julie
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Julie (Dingee) Carwellos
Web and IT Project Analyst, User Experience and Interaction Designer
LinkedIn <http://www.linkedin.com/in/jdingeecarwellos> -
http://www.linkedin.com/in/jdingeecarwellos
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