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In VisualWorks, instances of the Model class and the
DependentPart class work together. The work begins when the model
instance sends itself a change message:
*---------------*
I have changed! *------ | |
(change: message) | | Model |
*-----> | |
*---------------*
The sole purpose of a change message is to activate a method in the model that sends update messages to dependent parts, telling those dependent parts that a change in the model may require an update in the dependent parts:
*---------------* *---------------* | | I have changed! | | | DependentPart | <---------------------- | Model | | | (update: message) | | *---------------* *---------------*
Then, the dependent part examines the model to see what exactly has changed, and responds accordingly:
*---------------* *---------------* | | What is new? | | | DependentPart | ----------------------> | Model | | | (Mediated by getter) | | *---------------* *---------------*