MiG InfoCom MiG Calendar Tutorial - Manual (Page 19)

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3. The Command or CommandSet that should be executed. E.g.
StartAnimation .
A Command is a generic specification of an action that is to be taken
and what is the target. It can also be sub classes to support any action
that can be written in Java code, without the need for a specific
InteractionBroker .
An InteractionBroker is an executor/interpreter of Command s.
A broker will normally handle a certain type of commands, for example
the
ActivityViewInteractionBroker can handle commands
that will affect an ActivityView , it has specific knowledge on how
to manipulate it.
The Interaction framework is very loosely coupled. The different
parts, Interactor, Interaction, Command, Expression and
InteractionBroker have few demands on each other's types. This can
be confusing at first but is very powerful once understood. See the
examples in the AShape Tutorial for hints on how to use this powerful
and flexible framework.
One important functionality that the Interactor framework
supports is the notion of overriding attributes. If, for instance, an
AShape 's background color is normally blue, it can be overridden to
be yellow when the mouse is hovering over it. The original property of
the
AShape is never actually changed, it is just exchanged for the
overridden value when the attribute is fetched, for instance during the
paint process. The
Interactor keeps track of the overrides that is
currently active for its peer object, e.g. an ActivityView .
Geometry Package and Coordinates
Since the MiG Calendar requires a lot of flexibility when it comes to
positioning graphics on screen a new type of coordinates was
developed. All sub components within the component uses this
coordinating system. Classes that could denote statements like: '10
pixels from the end' and '20% in, but no less than 10 pixels from the
right edge'. These kind of statements is easy to do in Java code, but
quite hard to specify in a persistable object, such as a coordinate. The
util.gfx.geometry packages has these main parts:
• Numbers. A number can relate to 0, 1, or 2 other numbers. 0
means it is a value on it's own, such as an
Integer normally is. 1
means it needs one reference value in order to produce a number,
for instance when a coordinate denotes an offset or percentage. 2
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