Capability Properties


Certain properties cannot be set directly within a Service Object. This comes up most often in the case of capability properties; those with the Cap prefix in their names. According to the UPOS specification, these properties must be read-only; therefore, an implementation-specific mechanism is needed for the Service Object to change the value of these properties.

POS for .NET Base classes have a protected property, Properties, for this purpose. This property returns a helper class which has writable versions of the read-only properties implemented in the Base class. For example, PinPadBase has a property called Properties that returns an object of type PinPadProperties. And this object contains properties used to set various PinPad-specific capability properties, such as CapDisplay.

In addition to device-specific property classes, all POS for .NET Base and Basic classes also have a protected property called CommonProperties which returns an object of type CommonProperties. This helper class is used to modify capability and status properties found in PosCommon.

In general, a Service Object should always access the value of its common and class-specific properties using the helper classes. These properties may be written to by the Service Object and always contain the appropriate values.

The Service Object developer should be aware of what the POS for .NET framework may do when a particular value is changed. For example, the Service Object should generally not change CommonProperties.State since this may interfere with the POS for .NET internal state. Similarly, the Service Object developer should be aware that changing CommonProperties.PowerState may send a StatusUpdateEvent event to the application.

When deriving from the POS for .NET Base or Basic classes, the Service Object should generally not change the value of CommonProperties.State to ControlState.Closed. Doing so prevents cleanup of the event queue, and POS for .NET may later throw exceptions as it tries to process events already in the queue.