C# Interface

An interface in C# is a blueprint of a class that defines a set of methods and properties that a class can implement. In other words, an interface defines a contract that a class must adhere to. Interfaces provide a way to achieve polymorphism and abstraction in C#.

Declaring an Interface

To declare an interface, use the interface keyword followed by the interface name and its members. Here is an example:

1public interface IShape
2{
3    void Draw();
4    double Area { get; }
5}

The IShape interface defines two members, a method Draw() and a read-only property Area. Any class that implements this interface must provide an implementation for both of these members.

Implementing an Interface

To implement an interface, a class must include the interface's name in its declaration and provide an implementation for all the members defined in the interface. Here is an example:

1public class Circle : IShape
2{
3    public double Radius { get; set; }
4
5    public void Draw()
6    {
7        Console.WriteLine("Drawing Circle");
8    }
9
10    public double Area
11    {
12        get { return Math.PI * Radius * Radius; }
13    }
14}

In this example, the Circle class implements the IShape interface by providing an implementation for both the Draw() method and the Area property.

Implementing Multiple Interfaces

A C# class can implement multiple interfaces by including all the interface names separated by commas in its declaration. Here is an example:

1public interface IResizable
2{
3    void Resize(double factor);
4}
5
6public class ResizableCircle : IShape, IResizable
7{
8    public double Radius { get; set; }
9
10    public void Draw()
11    {
12        Console.WriteLine("Drawing Circle");
13    }
14
15    public double Area
16    {
17        get { return Math.PI * Radius * Radius; }
18    }
19
20    public void Resize(double factor)
21    {
22        Radius *= factor;
23    }
24}

In this example, the ResizableCircle class implements both the IShape and IResizable interfaces by providing an implementation for all the members defined in both interfaces.