What are Interfaces and Delegates in c#?

Question

Since i am new to c#, would like to know about Interfaces and Delegates in c#, the difference between them and scenarios both these to be used. Please don't provide any links, i would like an explanation in simple words.

Answer 1

An interface is a contract - it defines methods and properties that any implementing class has to have and as such any consumer of the interface will know they exist and can use them.

A delegate is a call back site - it defines a method signature that can invoke any method that has the same signature.

See delegates and interfaces on the C# programming guide.

An example of an interface is the IEnumerable interface. It only has one member defined - GetEnumerator. Any object that implements this interface will have this method and any code using such an object can call this method.

An example of a delegate is the Predicate<T> delegate. It is a generic delegate that is defines as following:

public delegate bool Predicate<in T>(T obj);

This means that it takes in any type T and returns a bool. Any method that takes a single type parameter and returns a bool is a match for this delegate and can be used with it.

Since delegates are also objects, they can be passed in to functions. So, any function that has a Predicate<T> delegate can pass in any mathod that matches it. Many of the Linq operators have delegates as parameters. See examples here.