[self-interest] Model View Controller and the Observer pattern

Jecel Assumpcao Jr jecel at merlintec.com
Sun Aug 26 22:53:16 UTC 2001


> Now I have a very specific question and for me it is very important
> it is answered in a scientifc way!!!

I think you ended up forgetting your question, for I didn't find it in 
the rest of the text. So I will suppose that you are interested in 
known if Self has an implementation of the Observer Pattern similar to 

The answer is: no. Morphic handles this in a less flexible way than 
MVC. Each object sends "changed" to itself whenever its internal state 
is changed and the same object should do something about it. The idea 
in Morphic is that each object should appear only once on the screen 
and so we don't need multiple viewers.

An exception to this is outliners, which when representing a morph can 
be on the screen at the same time as the morph itself. The morph "view" 
is updated by the "changed" code, but the outliner isn't. Instead, the 
outliner uses the periodic "step" method to poll the object and see if 
anything has changed. This is not efficient, but gets the job done. 
This is why an outliner sometimes takes several seconds to reflect 
changes to an object you have sent a message to.

Please note that the original creators of MVC are now using Morphic 

> As fundamental as the Observer appears to be in Smalltalk it is
> not a language feature (language feature and construct is the same
> thing?); it is a feature of most Smalltalk libraries.

Yes: language feature and language construct is the same thing. No: 
Observer is not a fundamental Smalltalk pattern. It is key to MVC, but 
you can have Smalltalks with other graphical systems and not need it at 
all. So it is a good thing that the ANSI standard ignores it.

-- Jecel

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