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// This array can only contain types that

// implement the IPointy interface.

IPointy[] myPointyObjects = {new Hexagon(), new Knife(),

new Triangle(), new Fork(), new PitchFork()};

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foreach(IPointy i in myPointyObjects)

Console.WriteLine("Object has {0} points.", i.Points);

Console.ReadLine();

}

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Source Code

The CustomInterface project is located under the Chapter 9 subdirectory.

Implementing Interfaces Using Visual Studio 2008

Although interface-based programming is a very powerful programming technique, implementing

interfaces may entail a healthy amount of typing. Given that interfaces are a named set of abstract

members, you will be required to type in the definition and implementation for 

each interface

method on 

each type that supports the behavior.

As you would hope, Visual Studio 2008 does support various tools that make the task of imple-

menting interfaces less burdensome. By way of a simple test, insert a final class into your current

project named PointyTestClass. When you implement IPointy (or any interface for that matter) on

a type, you might have noticed that when you complete typing the interface’s name (or when you

position the mouse cursor on the interface name in the code window), the first letter is underlined

(formally termed a “smart tag”). When you click the smart tag, you will be presented a drop-down

list that allows you to implement the interface (see Figure 9-7).

Figure 9-7.

Implementing interfaces using Visual Studio 2008

Notice you are presented with two options, the second of which (explicit interface implemen-

tation) will be examined in the next section. For the time being, once you select the first option, you

will see that Visual Studio 2008 has built generated stub code (within a named code region) for you

to update (note that the default implementation throws a System.Exception, which can obviously

be deleted).

namespace CustomInterface

{

class PointyTestClass : IPointy

{

#region IPointy Members

public byte Points

{

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get { throw new Exception("The method or operation is not implemented."); }

}

#endregion

}

}