Common Design Patterns for Symbian OS: The Foundations of Smartphone Software

4.1. Event Mixin

Intent

Save power and decouple your components by defining an interface through which event signals are sent to another component in the same thread.

AKA

Observer [Gamma et al., 1994]

4.1.1. Problem

4.1.1.1. Context

You wish to propagate event signals synchronously between an event generator and an event consumer operating within the same thread.

4.1.1.2. Summary

• You wish to reduce the power usage of your component.

• You want to promote encapsulation of and loose coupling between your event generators and event consumers so that testing and maintaining your component is made easier.

4.1.1.3. Description

An event generator wishes to propagate event signals to an event consumer that is running in the same thread. One way to do this would be to enable the event generator to make calls directly to the event consumer object's member functions. However, this promotes poor encapsulation (the event generator is able to call functions of the event consumer that are unrelated to event signaling) and tight coupling (the event generator is hardcoded to generate events for this specific event consumer).

4.1.1.4. Example

OBject EXchange (OBEX) is a communications protocol that defines a means for two devices to communicate by passing objects between them. The protocol defines the two ends of an OBEX communication session as the OBEX client and the OBEX server. The OBEX client drives communication by sending requests^[] to the OBEX server. The OBEX server is expected to ...