Mig-infocom MiG Calendar Tutorial Manual do Utilizador descarregar pdf (Página 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 Commands.

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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