Stephens' C# Programming with Visual Studio® 2010 24-Hour Trainer

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LESSON 27 Using interfaces

DEFINING INTERFACES

The preceding sections give examples that implement predefined interfaces. This section explains

how you can define your own.

Defining an interface is a lot like defining a class with two main differences:

First, you use the keyword

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interface instead of class in the declaration.

Second, you don’t provide any code for the properties, methods, and events that you declare

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in the interface.

The following code shows a simple

IDrawable interface. The code includes a using System.Graphics

directive at the top of the file to make working with

Brush, Pen, and Graphics objects easier.

interface IDrawable

{

int X { get; set; }

int Y { get; set; }

Brush Background { get; set; }

Pen Foreground { get; set; }

void Draw(Graphics gr);

}

A class that implements IDrawable must provide X, Y, Background, and Foreground properties, and

a

Draw method.

You cannot provide an accessibility modifier such as

private to the items defined by an interface.

They are always assumed to be public, and a class that implements the interface must declare these

items as

public.

The declarations for the properties look like they are providing a default implementation for them,

but they actually only define the required accessors. A class that implements

IDrawable must still

provide its own implementations, although that can use auto-implemented properties. For example,

the fol ...