What is the need of Interface in c# ?

Question

Please give a live example which describes the need of Interface in C# and how can it effect the functionality and performance of an application. Thanks in advance!

Vulpes · Answer

Interfaces are useful when a number of classes or structs which otherwise have no relation to each other share certain functionality even though they implement it in a different way. There are many examples of useful interfaces in the .NET Framework. Amongst the most useful are IEnumerable IEnumerator and their generic equivalents. These interfaces enable otherwise unrelated collections to be enumerated using 'foreach' and without them LINQ would not be possible. When you access methods through an interface reference the method called will be determined at runtime based on the actual type of the object. This 'late binding' does have a slight impact on performance as does calling virtual methods generally. Also if you assign a struct to an interface variable the struct needs to be 'boxed' on the heap which has a further impact on performance. However in the vast majority of applications the loss in performance is absolutely negligible and so interfaces should be freely used where it is appropriate to do so.