Interface Parameter

Provides access to a value of a Subject and meta-data such as name, a set of possible values and more. Part of the Observer design pattern which ensures that change notification happens regardless of how the value was changed. See Subject, Observer, Parameter for an overview.

It is very easy to connect a Parameter to a user interface control like NumericControl, ChoiceControl, or CheckBoxControl.

Parameter helps to minimize the knowledge that classes have about each other. For example, a NumericControl can display and modify the ParameterNumber of a Subject without knowing anything about the Subject other than it implements the Subject interface.

See Internationalization for information about localized and language-independent strings.

Getter and Setter Methods

A Parameter operates by calling getter and setter methods on its Subject. These methods are specified to the Parameter's constructor, and used in the Parameter's getValue and setValue methods. We assume that the Subject's setter method will perform notification of changes via Subject.broadcastParameter.

Here are examples of getter and setter methods showing how the Parameter is broadcast in the setter method of the Subject.

getMass(): number {
  return this.block_.getMass();
};

setMass(value: number) {
  this.block_.setMass(value);
  this.broadcastParameter(SingleSpringSim.en.MASS);
};
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Here is an example showing how the getter and setter methods are specified when creating a ParameterNumber. This is from SingleSpringSim:

this.addParameter(new ParameterNumber(this, SingleSpringSim.en.MASS,
    SingleSpringSim.i18n.MASS,
    () => this.getMass(), a => this.setMass(a)));
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Choices and Values

A Parameter can have a set of choices and values. If they are specified, then the Parameter value is only allowed to be set to one of those values.

• getValues returns a list of values that the Parameter can be set to.

• getChoices returns a corresponding list of localized (translated) strings which are shown to the user as the choices for this Parameter, typically in a user interface menu such as ChoiceControl.

When the set of Parameter choices is changed, a GenericEvent should be broadcast with the name CHOICES_MODIFIED. Then any control that is displaying the available choices can update its display.