On Jan 19, 2009, at 12:57 PM, Paul Bruneau wrote:
I'm confused by it, since I have been directed in the past by people
who know that The Cocoa Way is to have objects know how to draw
themselves--via a category if desired.
Is there differing opinion on this? (apparently there is...)
This is tough to generalize. There is not only differing opinion,
but also plenty of room for debate. :-)
In the Sketch example, there are different shapes (including
"text"), each of which handles drawing somewhat differently. I suspect
the decision not to put this into the canvas view is more a matter of
organization than architecture. I happen to agree with the decision.
There's nothing about the MVC design pattern that demands all
drawing code belongs in the view. In the particular case of a drawing
application where the shapes to be drawn *are* the data model, how to
draw a shape could be viewed as "business logic" for the model.
For the organizational argument, having a single view that includes
the logic to draw every kind of shape (including those added in the
future) seems messy and difficult to read / maintain. Stepping aside
from API architecture and design patterns, we would logically expect a
shape to be responsible for knowing how to represent itself. After
all, the canvas merely hosts the shapes (however they're drawn) and
provides UI interaction to manipulate them.
I'll remind everyone to consider my opening statement (hard to
generalize) if it seems like I'm contradicting myself. :-)
I am going to be starting a large app that will have many assemblies
and sub-assemblies that I want to draw. I had planned on the objects
drawing themselves. Should I revisit my thinking?
If the assemblies and sub-assemblies are all homogenous (in that
they all look more or less the same), I'd say yes, you should
reconsider the Sketch-like approach.
For an extremely over-simplified example, consider a view that
draws many labels. The shape, color, font, etc. of the labels are all
the same; merely the text is different. In that case, I'd have the
view be 100% responsible for all drawing.
Just my opinion, not an edict. :-)
--
I.S.
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