dimanche 29 avril 2018

Find a Decorator of a particular type when using the Decorator Pattern?

I'm building an app that needs to use multiple types of similar sensors. Since the sensors could also have different behaviours, or combinations of behaviours, I decided to use the decorator pattern.

In short, I have a hierarchy that looks like this:

enter image description here

So any of the concrete ISensorDecorator classes can decorate (wrap) any of the concrete IMeasureSensor classes, but since a concrete ISensorDecorator also is a concrete IMeasureSensor, they can wrap each other. So for example

IMeasureSensor sensor = new FilteredSensorDecorator(
    new CalibratedSensorDecorator(
        new AccelerometerSensor()
    )
);

is a valid statement that declares a filtered and calibrated accelerometer sensor.

Now let's say I have a method called setCalibration() in CalibratedSensorDecorator. Obviously I can't call

sensor.setCalibration();

because IMeasureSensor doesn't have a setCalibration() method. And trying to use

((CalibratedSensorDecorator)sensor).setCalibration()

won't work either, since sensor is a FilteredSensorDecorator.

How can I get to the CalibratedSensorDecorator in this particular case, and more generally to any specific decorator in any "chain" of decorators? I don't want to store them as separate variables, I want to do it dynamically.





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