C# tutorial – What is C# interface


C# tutorial : What is C# interface? – C# interface is programming construct which describes a group of related functionalities that can belong to any C# class or struct.

C# interface can be declared as follows:

interface IExampleInterface


string Property { get; set; }

void Function();

Event SampleEvent;

string this[int position]  { get;  set; }


C# interface can consist of:

  • Properties
  • Indexers
  • Events
  • Methods
  • Combination of above four

C# interface can not have:

  • Constants
  • Constructor
  • Static members
  • Operators
  • Function definitions

C# interface quick facts

  • All interfaces are by default public and abstract
  • All interface members also are public and can not have any access modifier
  • All non abstract classes or structure which implement interface must have definitions for al interface members and must match the signature.
  • Interface instance can not be created
  • Interface can inherit other interfaces
  • Classes and structs can inherit multiple interfaces
  • If method with same signature present in two or more interface then class can define InterfaceName.Method to differentiate
  • Classes withing different hierarchy can implement same interface
  • Interfaces can not be partially implemented. All interface members must be implemented.
  • If you are using PRISM then interfaces provides easier dependency injection mechanism
  • Interface provides guarantee of basic functionality and provides a contract
  • Interface also make your application scalable
  • Interface helps in providing standards to implementers
  • Interface provides run-time polymorphism
  • Relationship of class with interface is implements (Can do this) and not similar to abstract base class (IS-A)

How to implement interface in C# ?

public class ExampleClass : IExampleInterface


All definitions of interface members is must.

TIP: In Visual studio you can hover mouse over interface name in class file and you can implement all members of interface in one click.


Disadvantages of interface : When not to use interface?

  • When you want IS-A relationship
  • When class wants default functionality of some members
  • if members are going to change rapidly

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