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interface (C# Reference)

An interface contains only the signatures of methods, delegates or events. The implementation of the methods is done in the class that implements the interface, as shown in the following example:


      interface ISampleInterface
{
    void SampleMethod();
}

class ImplementationClass : ISampleInterface
{
    // Explicit interface member implementation: 
    void ISampleInterface.SampleMethod()
    {
        // Method implementation.
    }

    static void Main()
    {
        // Declare an interface instance.
        ISampleInterface obj = new ImplementationClass();

        // Call the member.
        obj.SampleMethod();
    }
}

An interface can be a member of a namespace or a class and can contain signatures of the following members:

An interface can inherit from one or more base interfaces.

When a base type list contains a base class and interfaces, the base class must come first in the list.

A class that implements an interface can explicitly implement members of that interface. An explicitly implemented member cannot be accessed through a class instance, but only through an instance of the interface, for example:

For more details and code examples on explicit interface implementation, see Explicit Interface Implementation (C# Programming Guide).

The following example demonstrates interface implementation. In this example, the interface IPoint contains the property declaration, which is responsible for setting and getting the values of the fields. The class Point contains the property implementation.

// keyword_interface_2.cs
// Interface implementation
using System;
interface IPoint
{
   // Property signatures:
   int x
   {
      get;
      set;
   }

   int y
   {
      get;
      set;
   }
}

class Point : IPoint
{
   // Fields:
   private int _x;
   private int _y;

   // Constructor:
   public Point(int x, int y)
   {
      _x = x;
      _y = y;
   }

   // Property implementation:
   public int x
   {
      get
      {
         return _x;
      }

      set
      {
         _x = value;
      }
   }

   public int y
   {
      get
      {
         return _y;
      }
      set
      {
         _y = value;
      }
   }
}

class MainClass
{
   static void PrintPoint(IPoint p)
   {
      Console.WriteLine("x={0}, y={1}", p.x, p.y);
   }

   static void Main()
   {
      Point p = new Point(2, 3);
      Console.Write("My Point: ");
      PrintPoint(p);
   }
}

Output

 
My Point: x=2, y=3

For more information, see the following sections in the C# Language Specification:

  • 1.9 Interfaces

  • 3.4.5 Interface members

  • 4.2.4 Interface types

  • 10.1.2.2 Interface implementations

  • 11.2 Struct interfaces

  • 13 Interfaces

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