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Most view components have a small number of distinct states
that determine how the view is configured and how it will
respond to the next program event. As a result, view
component programs typically consist of:
-
a constructor
than initializes the view,
-
a registration method for each program event source (e.g., a button)
that takes a callback (command) argument and
registers this callback as the listener for this
event source, and
-
a setter method for each distinct view state that sets the
fields of the view to the appropriate values.
The controller uses the registration methods to attach callbacks
to program event sources in the view. The callbacks use
the setter methods to change the state of the view in response
to program events.
For our click counter example, the view will have the following
format:
which we decompose into three possible states:
- 1.
- the Min state where the DEC and 0 buttons are deactivated
because the counter has its minimum value of 0.
- 2.
- the Counting state where are three buttons are activated,
and
- 3.
- the Max state where the INC button is deactivated because
the counter has reached its maximum value.
The listener must take into account the state of the model to update
view.
Next: 3.1.2.0.1 Warning
Up: 3.1 GUI Programming
Previous: 3.1.1 Model-View-controller Pattern
Corky Cartwright
2000-01-07