Am Do,28.08.2008 um 10:15 schrieb Oleg Krupnov:
Parts of your first question remind me of a situation that I had.
Erik Buck gave me some great advice and part of it was the following:
If you are worried about adding drawing code to a "Model" object,
add the drawing code in a category of <the model object>* and
maintain the category implementation in the "View" subsystem.
*I changed the words he used here because he used the name of my
specific class and I wanted to make it more readable in the general
case.
This will let you put a category into every view that you want to
so that your model objects get handled correctly for each view.
This may be indeed a good idea to use categories for this purpose. Is
it what everybody is using?
I have only one problem with this approach: As I mentioned before, I
need to add custom-view specific instance variables (states) to the
model object's category. The Objective-C categories do not allow
adding instance variables, only methods
I am considering to create a dictionary owned by the custom view,
containing state objects keyed by model object unique ID. This is a
kind of surrogate of subclassing the model objects inside the custom
view. I am not sure this is a good idea though. Are there other
approaches?
If I understood you correct, you think, that you fear a voilation of
the MVC pattern. Correct?
Think about some points:
- sometimes the shape or something like this is a true part of the
model. Think about predefined shapes and so on. So there is nothing
wrong in storing that informtion in the model.
- Can you isolate the "shape-part" (model) from the drawing part
(obviously depending on view states)?
Just an example: I had a graphic application that drawed some inserted
shapes. The shape itself is a part of the model, the color of the
shape, too. But when the user selects a shape (symbol), the color
should change. So the drawing of the shape depends on a view property.
I think, this is the core of your problem.
I solved it by returning only bezier paths and colors from the model.
So the shape itself (model) is still a part of the model, but the
drawing (depending on the view) is done inside the view. (Simply by
stroking the paths.)
Cheers,
Amin
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