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In Chapter 39, you learned that you can define setters for various
instance variables in a model such that those setters send changed:
messages, which in turn cause model instances to send update:
messages to dependent parts. It was up to you to decide which setters
send changed: messages.
The ValueHolder class comes equipped with one instance variable,
value, with a getter, value, and a setter,
value: (inherited from the ValueModel class), for the
value instance variable. The setter sends the changed:
message with #value as the aspect argument:
ValueHolder class definition Object subclass: #ValueHolder instanceVariableNames: 'value' classVariableNames: '' poolDictionaries: '' category: 'Interface-Support' ValueHolder method definition • instance value ^ value ValueModel method definition • instance value: newValue value := newValue self changed: #value