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Understanding Callback Interfaces

Beyond using interfaces to establish polymorphism across diverse class hierarchies, namespaces,

and assemblies, interfaces may also be used as a 

callback mechanism. This technique enables

objects to engage in a two-way conversation using a common set of members.

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Note

The .NET platform provides a formal fabric used to build events (which is quite different from the tech-

nique that will be shown here). As you will see in Chapter 11, delegates, events, and lambdas are the standard way

to enable objects to chit-chat back and forth.

To illustrate the use of callback interfaces, let’s update the now familiar Car type in such a way

that it is able to inform the caller when it is about to explode (the current speed is 10 miles below

the maximum speed) and has exploded (the current speed is at or above the maximum speed).

Begin by creating a new Console Application named CallbackInterface. The ability to send and

receive these events will be facilitated with a new custom interface named IEngineNotification: